It's the BSM thread! This is the place where people can seek help with their homework or ask for help understanding questions where the answer isn't necessarily expected of people taking the MCAT. Since most premeds have similar sorts of undergraduate majors, hopefully if anyone needs help in their undergraduate homework or wants further clarification, then they can ask the question here and hope for some help. Of course, there's no guarantee that someone can answer any given question, but it's here now, and you can give it a try.

Acceptable topics include:
Advanced science questions in bio, physics, chemistry, etc
Mathematics
Engineering
Psychology
Cognitive science

Unacceptable topics include:
Anything actually required for the MCAT
Non-science questions

My undergraduate majors were chemical engineering and molecular and cell biology (neuro emphasis). Hopefully some of the bright people on these boards will drop in regularly. Even if you can't help, you might learn something, and that's basically what this thread is all about.

Cheers!

What fun this will be. OK, me first. No rhetorical questions from me -- I'll ask stuff I really want to know.

What is the modification to the Bernoulli equation for compressible materials? Under what conditions does the compressibility become significant? (We neglect it all the time, conceptually, when dealing with air -- how far off are we?)

What happens to the Bernoulli equation at supersonic speeds? An engineer student of mine once told me that, at supersonic speeds in air, as pressure decreases speed increases -- thus the shape of rocket engine nozzles, which increase the speed of the exhaust flow. Assuming this is true, why?

Why does Bernoulli not work for blood flow through our circulatory system -- is it energy loss due to vicosity, vessel wall elasticity, or something else?

Why are we here? What is the meaning of life?

(or would these be more relevant to the Verbal thread?)

What fun this will be. OK, me first. No rhetorical questions from me -- I'll ask stuff I really want to know.
What happens to the Bernoulli equation at supersonic speeds? An engineer student of mine once told me that, at supersonic speeds in air, as pressure decreases speed increases -- thus the shape of rocket engine nozzles, which increase the speed of the exhaust flow. Assuming this is true, why?

Not a complete answer, but a fascinating discussion:
http://www.engapplets.vt.edu/fluids/CDnozzle/cdinfo.html

Not a complete answer, but a fascinating discussion:
http://www.engapplets.vt.edu/fluids/CDnozzle/cdinfo.html
Thanks for the link -- it answers some of my questions, and as you said is fascinating. But I still want to know why supersonic flow accelerates as it expands.

Thanks for the link -- it answers some of my questions, and as you said is fascinating. But I still want to know why supersonic flow accelerates as it expands.
According to the article, it accelerates because it can. The driver is the pressure differential between the engine and the ambient pressure. The expansion permits continued accceleration along the differential rather than an abrupt shift to subsonic due to the shock wave.

An arrow leaves a bow at a speed of 43.6 m/s. If the bow exerted an average force of 95N on the arrow, how far did the archer pull back the bow string?

An arrow leaves a bow at a speed of 43.6 m/s. If the bow exerted an average force of 95N on the arrow, how far did the archer pull back the bow string?
You need the mass of the arrow, or an approximation.

You need the mass of the arrow, or an approximation.

That's what I'm saying.... just curious if anyone knew any other way.

That's what I'm saying.... just curious if anyone knew any other way.
Or the amount of time that the arrow + string is accelerating.

Or the amount of time that the arrow + string is accelerating.
That would help. Unfortunately that's all the question says.

Another Question:
A boy jumps vertically upwards from the top of a platform and then drops on a trampoline below which is 3m below his starting point.

If the trampoline has an effective spring constant of 5.2*10^4 N/m and is depressed 0.35m , calculate the boy's initial upward velocity.

That would help. Unfortunately that's all the question says.

Another Question:
A boy jumps vertically upwards from the top of a platform and then drops on a trampoline below which is 3m below his starting point.

If the trampoline has an effective spring constant of 5.2*10^4 N/m and is depressed 0.35m , calculate the boy's initial upward velocity.
Also insoluble without the mass of the boy. You could assume, say, 25 kg and work through it.

Molecular self-assembly has always been a mystery to me. I mean, I know how it works in theory, but I have a difficult time wrapping my mind around it. It doesn't seem real to me. Can anyone help?

Along the same lines, I am mystified by cellular processes' self-activation. We anthropomorphize these processes and pretend that there's someone pulling the strings, but in reality it all just sorta happens in order to satisfy the 2nd law of thermodynamics, right? Or am I missing something.

And on a larger scale, this all ties into theories of consciousness and free will. If everything we do is essentially a response to thermodynamic pressure - is all an exercise in physics - then where do consciousness and free will come in? I mean that in theory given sufficient computational power and knowledge of biological systems, one could predictively compute whether I'm going to succeed in medical school, or fail. But it *feels* like it's going to depend more on whether I bother to get off my ***** on Saturday mornings to go study than on some predetermined physical equation. I keep coming back to the insufficiency of science to explain the human condition. As I am an atheistic-leaning secular humanist, this inability to accept these implications of the "scientific" explanation of the cosmos really bothers me.

OK, so this question is moving into metaphysics, but at least it's beyond the scope of the MCAT, right?

Molecular self-assembly has always been a mystery to me. I mean, I know how it works in theory, but I have a difficult time wrapping my mind around it. It doesn't seem real to me. Can anyone help?

Do you mean protein folding? :confused:

Along the same lines, I am mystified by cellular processes' self-activation. We anthropomorphize these processes and pretend that there's someone pulling the strings, but in reality it all just sorta happens in order to satisfy the 2nd law of thermodynamics, right? Or am I missing something.

Yeah, pretty much. It's easier to imagine, say, water running down hill. It's easy to look at a patch of ground in some random part of the St Lawrence River watershed, and say: "okay... If I dump some water right here, or right there, with all the possible directions it can possibly go, it's going to end up passing Quebec City, and getting dumped into the Atlantic at the precise location of the St Lawrence delta. Yeah, right." It's a bit easier for us to imagine this sort of thing, because we have an innate understanding of the differences between going uphill and going downhill. We have a harder time imagining the difficulty of going against a chemical potential gradient, or an electric gradient. It's easy for us to imagine throwing a bunch of hockey pucks across a frozen pond, and them all ending up stuck in the snow along the sides, "miraculously" being self-segregating from the slick surface; but it's harder to imagine a Van der Waals interaction forcing the self assembly of a lipid bilayer. But in the long run, they're really all the same.

Chemicals are banging around at high speeds. They make a billion wrong collisions, but when they make that one right collision, the action happens, and the wrong collisions don't even matter anymore.

On some drops of water in the watershep might end up in some dead-end pond somewhere, yes. And some proteins don't fold right, and sometimes an ion channel just gets bumped open at the wrong time, or fails to open at the right time. But in the long run, you end up with a statistical average that acheives the needed result. Send a man to war against an army, he will die. Send a million men, and many will die, but the army will be defeated, and the losses lose significance in the long run. We know only the name of Waterloo as the place where Wellington defeated Napolean, but we do not know the name of the individual Brittish soldier who was defeated by a Frenchman that day.

The law of mass action: thermodynamics, sociology, economics, and evolution are all similarly governed.

And on a larger scale, this all ties into theories of consciousness and free will. If everything we do is essentially a response to thermodynamic pressure - is all an exercise in physics - then where do consciousness and free will come in? I mean that in theory given sufficient computational power and knowledge of biological systems, one could predictively compute whether I'm going to succeed in medical school, or fail. But it *feels* like it's going to depend more on whether I bother to get off my ***** on Saturday mornings to go study than on some predetermined physical equation. I keep coming back to the insufficiency of science to explain the human condition. As I am an atheistic-leaning secular humanist, this inability to accept these implications of the "scientific" explanation of the cosmos really bothers me.

OK, so this question is moving into metaphysics, but at least it's beyond the scope of the MCAT, right?

I copy/pasted my free will argument from an old thred. Basically, I regard the question as a false dichotomy, and as a question that is intrinsically meaningless--akine to "what color is the sound of the wind blowing through the trees?" You might come up with a poetic answer, but not a meaningful one.

Either the universe is deterministic, and everything will occur as a direct, unchangeable product of laws (be they scientific principles or the word of God), or there is something called free will wherein individuals are able to make choices, and they may make any choice they want, and physical laws only affect their manifestation of those choices, but the choices themselves are determined by something beyond the deterministic machine. This is a false dichotomy, and the two options give the exact same results anyways.

The whole thing seems to hinge upon the outcome of a make believe scenario. God comes down from the heavens, (or a super-genius with eight billion Cray supercomputers wired together chugging all the data of the velocity and location of all matter), and says: "I have seen the future, and in my infinite wisdom, I can see that you are going to lose $50 betting on the Super Bowl this year." And then we all wonder, can you decide to not bet that money so that you will not meet the deterministic fate?

The question becomes "can an entity observe two parallel universes that are completely identical in every physical aspect (molecular location and momentum, etc), and can two different outcomes result from a non-physical difference between the two, where an individual "wills" different activity? It might as well be "can God microwave a burrito so hot, even He couldn't eat it?"

Well, when that happens, I'll start to worry about free will. In the mean time, it's pretty clear that it's a moot question, with no discernable differences in the outcomes I'm capable of perceiving.

Nutmeg, I really like your answer to the second of my questions. For the first, I was thinking not just of protein folding, but of all biological processes where atoms seem to just "migrate" to their expected locations in a molecule. I'm not saying this well. But I think your answer to my second question answers this as well.

As for your answer to my third question, I must say your pragmatic approach makes sense, but I still find it unsatisfying. Here's an interesting passage on scientific determinism, from here (http://www.answers.com/main/ntquery;jsessionid=9kq0hkd2fjdeh?tname=determinism&curtab=2222_1&hl=scientific&hl=determinism&sbid=lc01a):
Modern perspectives on determinism

Scientific determinism and first cause
Since the early twentieth century when astronomer Edwin Hubble first hypothesized that red shift shows the universe is expanding, prevailing scientific opinion has been that the universe started with a Big Bang, and therefore has a finite age. Different astrophysicists hold different views about precisely how the universe originated (Cosmogony), but a consistent viewpoint is that scientific determinism has held at the macroscopic level since the universe came into being.


Determinism and generative processes
In emergentist or generative philosophy of cognitive sciences and evolutionary psychology, free will is the generation of infinite behaviour from the interaction of finite-deterministic set of rules and parameters. Thus the unpredictability of the emerging behaviour from deterministic processes leads to a perception of free will, though free will as an ontological entity does not exist.

As an illustration, the strategy board-games chess and Go have rigorous rules in which no information (such as cards' face-values) is hidden from either player and no random events (such as dice-rolling) happen within the game. Yet, chess and especially Go with its extremely simple determinstic rules, can still have an extremely large number of unpredictable moves. By analogy, emergentists or generativists suggest that the experience of free will emerges from the interaction of finite rules and deterministic parameters that generate infinite and unpredictable behaviour.

Dynamical-evolutionary psychology, cellular automata and the generative sciences, model emergent processes of social behaviour on this philosophy, showing the experience of free will as essentially a gift of ignorance or as a product of incomplete information.

I like the Go analogy in particular.

Nutmeg, I really like your answer to the second of my questions. For the first, I was thinking not just of protein folding, but of all biological processes where atoms seem to just "migrate" to their expected locations in a molecule. I'm not saying this well. But I think your answer to my second question answers this as well.

As for your answer to my third question, I must say your pragmatic approach makes sense, but I still find it unsatisfying. Here's an interesting passage on scientific determinism, from here (http://www.answers.com/main/ntquery;jsessionid=9kq0hkd2fjdeh?tname=determinism&curtab=2222_1&hl=scientific&hl=determinism&sbid=lc01a):
Modern perspectives on determinism

Scientific determinism and first cause
Since the early twentieth century when astronomer Edwin Hubble first hypothesized that red shift shows the universe is expanding, prevailing scientific opinion has been that the universe started with a Big Bang, and therefore has a finite age. Different astrophysicists hold different views about precisely how the universe originated (Cosmogony), but a consistent viewpoint is that scientific determinism has held at the macroscopic level since the universe came into being.


Determinism and generative processes
In emergentist or generative philosophy of cognitive sciences and evolutionary psychology, free will is the generation of infinite behaviour from the interaction of finite-deterministic set of rules and parameters. Thus the unpredictability of the emerging behaviour from deterministic processes leads to a perception of free will, though free will as an ontological entity does not exist.

As an illustration, the strategy board-games chess and Go have rigorous rules in which no information (such as cards' face-values) is hidden from either player and no random events (such as dice-rolling) happen within the game. Yet, chess and especially Go with its extremely simple determinstic rules, can still have an extremely large number of unpredictable moves. By analogy, emergentists or generativists suggest that the experience of free will emerges from the interaction of finite rules and deterministic parameters that generate infinite and unpredictable behaviour.

Dynamical-evolutionary psychology, cellular automata and the generative sciences, model emergent processes of social behaviour on this philosophy, showing the experience of free will as essentially a gift of ignorance or as a product of incomplete information.


I like the Go analogy in particular.
As for molecular movement, one must regard that the Universe doesn't care which atom does what. With diffusion don a chemical gradient, for instance, there really isn't a driving force for change, because there really isn't any real thing that's changing other than a statistical average. If you put 158 preschoolers on a footbal field blind folded, and you have them all in a 10' radius circle, and you tell them all to run around for five minutes, they'll end up scattered all over the field. But if you have them all scattered all over the field, and you tell them to run around, it is highly unlikely that they will end up in the circle.

But let's think about reaction at a catalyst. Let's say that all the kids are swinging wiffle ball bats wildly, and they tend to get away from one another and spread out as much as they can. If you then say that anyone who ends up in the 10' circle will immediately be removed from the field, then you will create a void around the circle. This means that there's a better chance statistically of going from being not near the circle to being near it, than there is to go from being near the circle to being not near it, for the simple reason that if you are near the cirlce, you have a chance of being in the circle soon after and getting whisked away. Kids can go from where they are to where they're not, but they can't go from where they're not to where there are already kids. Chemicals work in the same way.

My problem with the quoted bit is that it might try to refute determinism, but it doesn't refute or confirm free will. If there is randomness--as quantum mechanics strongly suggests--then that does not necessarily mean that the open space for change without direct physical causation is necessarily filled by a non-physical entity called "free will."

So, is free will the manifestation of physical law, or is free will a non-physical dynamic that influences physical phenomena? And what happens when the immovable object is struck by the unstoppable force?

SO here's my boggle: I was on another forum and someone asked,

"I am confused over entropy in relation to equilibrium. Is the change in S of the system 0 at equilibrium? or does the change in entropy of the universe equal 0 at equlibrium? I am also unsure of the equation change in S= dqrev./ T. When does this equation apply?"

To which I responded:

Since the deltaS = S(final-initial) the CHANGE in S will be 0 @ equil.

Maximum entropy:

deltaS of the universe = 0 at equilibrium, where we all want to be.
This means that the change in both the environment and the system are… well, not changing and = 0

When you’re not at equilibrium, somebody has got to be changing so you can get there. This is when a reaction is spontaneously heading to equilibrium and it looks like this:

DeltaS universe = deltaS system + deltaS surroundings > 0


I don't know what to do with the heat added to the system over absolute T as I don't really get it. ...?
Also, I think that saying that the equation spontaniously heads to equilibrium is misleading as the entire process is measured by deltaG. Is it o.k. to say that IF it were only up to the change in entropy, it would be spontanious?
What a debacle!
:barf:

I don't know what to do with the heat added to the system over absolute T as I don't really get it. ...?
Also, I think that saying that the equation spontaniously heads to equilibrium is misleading as the entire process is measured by deltaG. Is it o.k. to say that IF it were only up to the change in entropy, it would be spontanious?


I am going to move this discussion to the non-MCAT science questions since this is way beyond what you need to know for MCAT-level general chemistry. ;)

The equation deltaS = qrev/T is the definition of entropy for a reversible reaction according to the Second Law of Thermodynamics. The First Law tells us that we have two forms of energy: heat, which is not directed, and which therefore increases entropy (qrev = heat due to a reversible process) and work, which is directed, and therefore does not increase entropy (that's why work does not appear in the definition of entropy).

You are correct that spontaneity is measured by deltaG. The value of deltaS can be positive or negative for a spontaneous reaction, depending on the values of deltaH and T, the absolute temperature. I think what you said is probably ok given your caveat about assuming you can neglect the enthalpy.

Why does Bernoulli not work for blood flow through our circulatory system -- is it energy loss due to vicosity, vessel wall elasticity, or something else?
Which version of the Bernoulli Equation are you talking about? In mass transfer, we used something called "the Engineering Bernoulli," which was big, ugly, and accounted for all sorts of crazy crap. However, I do know that blood flow must take into account viscous losses, and the viscosity is related to the sheer rate (ie mu =/= constant).

Here's one link I managed to find: http://advan.physiology.org/cgi/content/full/25/1/44

I'm also thinking that there may be a problem with the irrotational requirement for the Bernoulli equation. Since blood contains particles with much higher rotaional inertia than the average molecule, there's a good chance that there would be a need to consider curl, which even the Engineering Bernoulli doesn't do.

Alright, question for shrike or some other physics pro out there:

I was adding water to a tank on a scale, and I added the water at an angle so that the water was spinning furiously inside the tank. The dude I was working with asked if that wouldn't effect the weight, becuase the added rotational inertia. I said no, it wouldn't because gravitation effects mass and it doesn't increase the mass. Besides that, by experience I know that the weight shown on the scale doesn't drop when the water stops spinning, although the spinning water definitely makes the tank harder to push.

But I got to thinking about this. The force of gravity is proportional to the mass of the object, and the acceleration of the object is a equally proportional to the mass. In my physics class, I remember this being stated as the reason why two objects of different masses fall at the same rate: they experience different forces that differ in proportion to the degree to which the forces make the masses accelerate. Hence, they accelerate at the same rate because the mass of the falling object cancels out of the equation.

But what about two objects of the same mass, one spinning, one not? They both have the same gravitational attraction, but one has more inertia. Yet I would expect that they would fall at the same rate, wouldn't they?

What gives??? :confused: :confused: :confused:

But what about two objects of the same mass, one spinning, one not? They both have the same gravitational attraction, but one has more inertia. Yet I would expect that they would fall at the same rate, wouldn't they?

It'll be best to consider this in light of relativity, if you're referring to a situation in a vacuum then I would imagine that they would fall with the same accerelation. Einstein thought about similar situations, except that he eventually figured that space is curved from such propositions;)

Weird question.... warning!

Why is it that when you're eating wasabi peas and you bite into that really potent one, fire seems to shoot up through your nose and shoot out flames?? Physiologically, what is going on? Curoius minds, want to know..! :p

How is this possible????? How can .99999.........=1.0000000......?????


Don't believe me?

let x=0.9999999............

10x=9.9999999999..........
-x=-0.9999999999.........
--------------------------
9x=9.000000000000000.....


x=1, therefore 1=0.9999999................
:D :D :D :D :D :D :D

That's one way to look at it. Another is to say that

(1/3) = 0.333333333

3 * 0.333333333 = 0.99999999999
and yet
3 * (1/3) = 1.0000000000000

Or, if you want something more formal, I found this:

http://mathforum.org/dr.math/faq/faq.0.9999.html

How about this one. Draw a right triangle with sides of length 1 and hypotenuse square root of 2. Obviously the length of the hypotenuse is greater than the length of each side. however, draw a straight line from the hypotenuse perpendicular to the side opposite the hypotenuse. Do this as many times as you wish. What you effectively have done is made a function from the set of all points making up the hypotenuse to the set of all points making up the side of length 1. How is this significant? You just matched two infinite sets with each other and showed that they were the same size. There are as many points in the interval [0,1] as there are many points in the interval [0,2]! Try this, try to think of a way to match all the integers {......-2,-1,0,1,2.......} to the infinite infinte amount of points in the interval [0,1]. Once you have exhausted yourself, you will realize it can't be done! There are obviously an infinite amount of integers, as well as an infinite amount of numbers between 0 and 1, so why can't it be done? here's why--there are actually different sizes of infinity! in fact, there are an infinite amount of different sizes of inifinty!

How about this one. Draw a right triangle with sides of length 1 and hypotenuse square root of 2. Obviously the length of the hypotenuse is greater than the length of each side. however, draw a straight line from the hypotenuse perpendicular to the side opposite the hypotenuse. Do this as many times as you wish. What you effectively have done is made a function from the set of all points making up the hypotenuse to the set of all points making up the side of length 1. How is this significant? You just matched two infinite sets with each other and showed that they were the same size. There are as many points in the interval [0,1] as there are many points in the interval [0,2]! Try this, try to think of a way to match all the integers {......-2,-1,0,1,2.......} to the infinite infinte amount of points in the interval [0,1]. Once you have exhausted yourself, you will realize it can't be done! There are obviously an infinite amount of integers, as well as an infinite amount of numbers between 0 and 1, so why can't it be done? here's why--there are actually different sizes of infinity! in fact, there are an infinite amount of different sizes of inifinty!

My Calc I professor referred to two different types of infinity: the "countably infinite" (like the number of positive intigers) and the "incountably infinite" (like the number of irrational numbers between 0 and 1). The proof he gave for the fact that there are more numbers between 0 and 1 than there are positive intgers is this: For any positive integer you can name, there is a number between 0 and 1 that looks like that same integer with a decimal point in front of it. That's one-to-one. But for each of those numbers, you could put an infinite number of zeros between the decimal and the first digit.

Howdy SuperTroopers,

There I lay last night, "WHY?!" my mind screamed out in the darkness. Why is the work created by friction = (Fd cos theta)?

I tried to derive it from the opposite side, (created by F cos theta), but then I ended up with W= Fd as W=d(d) which I think is going in the wrong direction anyway. Actually, I'm a ninny - none of the above makes sense.

So, I need to know how you get the force acting on the adjacent side, (friction), when I have the hypotenuse F, the adjacent d and the angle between. How is such an equation made?

Caboose.

THEN...

I was looking at viruses. I'm convinced they are man-made disease carriers from the future to control populations designed by someone who played a lot of virtual Dungeons and Dragons. What odd little packages they are.

So, some viruses contain enzymes to digest the host cell membrane and all contain either DNA or RNA. Their capsid is a mere shell of love that is sometimes cuddled by a lipid rich envelope. Why is it so difficult for us to "kill" the things? Endospores must engulf themselves in layers and layers of membrane in order to remain dormant for hundreds of years, but viruses can withstand ALL SORTS of torture and happily go about their business with one layer.

If, somehow, one removes the harmful DNA from these capsids, the spike proteins on the empty virus can be used in vaccines. How are these proteins not denatured under harsh conditions?
(Is AIDS a rapidly mutating virus being that they can't make a vaccine?)

Just curious.
Caboose.

Why is it so difficult for us to "kill" the things? Endospores must engulf themselves in layers and layers of membrane in order to remain dormant for hundreds of years, but viruses can withstand ALL SORTS of torture and happily go about their business with one layer.Do they though? Viruses are generally pretty easy to kill outside the body, for the short time they survive. What makes them so tough is that we are trying to kill something that's residing in our own cells, so we have to selectively kill them without killing ourselves.

When we do find a way to get them (e.g. reverse transcriptase inhibitors) they, being such rapidly mutating little buggers, quickly evolve a new version of whatever's been targeted.

(Is AIDS a rapidly mutating virus being that they can't make a vaccine?)Yes. Crazy fast.

How are these proteins not denatured under harsh conditions? You mean in vaccine prep? It may be the conditions are optimised so that the protiens stay intact or in some cases they may be so simple that they'll refold properly after denaturation. More than likely, the proteins are totally denatured but it doesn't matter. Antibodies are created to epitopes (small regions of antigenicity) not necesarily the entire protein. Indeed, some vaccines are peptides -- just small portions of the antigenic proteins.

Howdy SuperTroopers,

There I lay last night, "WHY?!" my mind screamed out in the darkness. Why is the work created by friction = (Fd cos theta)?

I tried to derive it from the opposite side, (created by F cos theta), but then I ended up with W= Fd as W=d(d) which I think is going in the wrong direction anyway. Actually, I'm a ninny - none of the above makes sense.

So, I need to know how you get the force acting on the adjacent side, (friction), when I have the hypotenuse F, the adjacent d and the angle between. How is such an equation made?

Caboose.

I'm not quite clear on what you are asking. Anyway, work is defined as the force vector dotted into the directional vector. Mathematically the dot product of two vectors is defined as the magnitude of the 1st vector times teh magnitude of the 2nd vector times the cosine of the angle between them.

Do they though? Viruses are generally pretty easy to kill outside the body, for the short time they survive. What makes them so tough is that we are trying to kill something that's residing in our own cells, so we have to selectively kill them without killing ourselves.

When we do find a way to get them (e.g. reverse transcriptase inhibitors) they, being such rapidly mutating little buggers, quickly evolve a new version of whatever's been targeted.

Yes. Crazy fast.

You mean in vaccine prep? It may be the conditions are optimised so that the protiens stay intact or in some cases they may be so simple that they'll refold properly after denaturation. More than likely, the proteins are totally denatured but it doesn't matter. Antibodies are created to epitopes (small regions of antigenicity) not necesarily the entire protein. Indeed, some vaccines are peptides -- just small portions of the antigenic proteins.

Quick and helpful - very nice! Thanks!

Novawildcat - indeed, that is the product of Caboose chasing her tail. I don't understand where the force of friction comes from - how it is derived from the vectors. I'm not very up on the physics yet, so perhaps I can study a little and add onto this question to make it make sense. :o
Thanks for the dot product info, perhaps I can investigate...
Caboose.

The force due to friction can only be determined experimentally. F=uN where u=coefficient of friction and N is the normal force (this is the definition of friction). u is determined through experimentation. If we think about this in vector terms your have the force vector due to friction acting in one direction and the object moving in some other direction s (which is the displacement vector). By definition the work done by friction would be the magnitude of F times the magnitude of s times the cosine of the angle between those vectors.

Alright, question for shrike or some other physics pro out there:

I was adding water to a tank on a scale, and I added the water at an angle so that the water was spinning furiously inside the tank. The dude I was working with asked if that wouldn't effect the weight, becuase the added rotational inertia. I said no, it wouldn't because gravitation effects mass and it doesn't increase the mass. Besides that, by experience I know that the weight shown on the scale doesn't drop when the water stops spinning, although the spinning water definitely makes the tank harder to push.

But I got to thinking about this. The force of gravity is proportional to the mass of the object, and the acceleration of the object is a equally proportional to the mass. In my physics class, I remember this being stated as the reason why two objects of different masses fall at the same rate: they experience different forces that differ in proportion to the degree to which the forces make the masses accelerate. Hence, they accelerate at the same rate because the mass of the falling object cancels out of the equation.

But what about two objects of the same mass, one spinning, one not? They both have the same gravitational attraction, but one has more inertia. Yet I would expect that they would fall at the same rate, wouldn't they?

What gives??? :confused: :confused: :confused:

Someone correct me if I am wrong, but I think that there are higher order terms in relativistic gravitational that are due to things like rotation.

I was watching this neurosurgery where the surgeon broke through the dura and cerebrospinal fluid started to pump out. What drives this? If there is such a force driving the circulation of the CB fluid, why is it necessary for ciliated ependymal cells?

Simple? :o

Caboose.

no love for neuro. :(
Caboose.

no love for neuro. :(
Caboose.

Sorry, caboose, I don't know the answer to this one. Maybe you could ask in the surgery or neurology residency forums?

Sorry, caboose, I don't know the answer to this one. Maybe you could ask in the surgery or neurology residency forums?

Oooh! Thanks for answering. I thought the thread might have died and no one told me. I never thought to venture over there.

I got another one, wanna try?
It was dark and sultry... it was the jejunum.
The triglycerides were ripped apart violently in the lumen by the evil Lipase. The monoglycerides and fatty acids huddled together in a small micelle, emulsified in bile. I don't know if you've ever been emulsified in bile, but it's not pleasant and the fats raced to the membrane to save themselves. They diffused through the nonpolar bilayer and popped into the enterocyte who immediately put them back together into tryglycerides and shipped them off to the s.ER, to the Golgi and eventually spit them out into the interstitial space as chylomicrons.

So... why does lipase have to break up triglycerides into monoglycerides for shipment into the cell where the reverse reaction will take place immediately anyway? Why are triglycerides not able to form micelles and diffuse as they are? Are the triglycerides modified in the enterocyte so that they are different from those still in the lumen?
What did you eat for lunch?
:D
Caboose.

Sorry, caboose, I don't know the answer to this one. Maybe you could ask in the surgery or neurology residency forums?

Look what Nate gave me!

CSF is made mainly by secretary cells in the choroid plexus within the 3rd ventricle of the brain (deep above the spinal cord). From there it travels down the aqueduct of Sylvius (great vacation spot ) and down the central canal of the spinal cord and out holes into the subarachnoid space. It then is able to pass through one-way valves into venous sinuses where it is removed into circulation. So, there is a constant formation and removal of CSF that creates a flow. The fluid also protects the brain from the pulsing blood vessels around it which would squish the brain with each systole. Kind of like a hydraulic shock absorber. This is probably what creates the "pulsing" ejection of fluid in a wound.
Anyway, that is my interpretation and I hope that is all correct since I have an exam on it in a week.
Peachy keen!!
Caboose.

lol, no, the forum is still going. But I've never studied neurosurgery, so I wouldn't even know where to start with that other one. ;) BTW, there is a separate neurosurgery residency forum. You might also try asking in the MSTP forum if the surgeons and neurologists can't help you.

Your new question is interesting (and if nothing else, you can always become a mystery writer if you change your mind about med school!). I can answer part of it: triglycerides aren't polar like glycerol is, and they don't have a charged polar end like their fatty acid precursors do. So triglycerides can't form micelles. But as to why the triglycerides don't just diffuse across the membrane on their own, I don't know. Ditto about whether the enterocytes modify them in some way when re-assembling them. Any of you cell bio people around?

P.S. It's only 11AM, so I didn't eat lunch yet. But when I do, I plan to have some chocolate cake. It's chock-full of triglycerides, which will be dismembered, and I won't feel the least bit sorry about it. :p

Look what Nate gave me!

CSF is made mainly by secretary cells in the choroid plexus within the 3rd ventricle of the brain (deep above the spinal cord). From there it travels down the aqueduct of Sylvius (great vacation spot ) and down the central canal of the spinal cord and out holes into the subarachnoid space. It then is able to pass through one-way valves into venous sinuses where it is removed into circulation. So, there is a constant formation and removal of CSF that creates a flow. The fluid also protects the brain from the pulsing blood vessels around it which would squish the brain with each systole. Kind of like a hydraulic shock absorber. This is probably what creates the "pulsing" ejection of fluid in a wound.
Anyway, that is my interpretation and I hope that is all correct since I have an exam on it in a week.
Peachy keen!!
Caboose.

cool. Thanks for sharing. :)

P.S. It's only 11AM, so I didn't eat lunch yet. But when I do, I plan to have some chocolate cake. It's chock-full of triglycerides, which will be dismembered, and I won't feel the least bit sorry about it. :p

:laugh: Poor little guys probably never know what hit 'em.
Evidently, triglycerides would have to be transported via proteins which would be about as easy as birthing.

I'll be back soon. :)
Thank you so much for your help!!!
Caboose.

It seems as if gene therapy is again advancing inti clinical trials. Does anyone have any experience/info on adenoviruses & why they seem to be a promising transfer vector.

Tonight I was talking with a friend. Long story short: I said that when an iceberg melts, the water level will be the same before and after. He said he dont buy it because most of the iceberg is below the surface of the water and solid water takes up more volume than liquid water. He thinks that water levels will decrease. I couldnt figure out a good way to explain to him why this is not true. It is just something I THOUGHT i always knew. After searching the internet, I have found many scientists who say water levels would increase, some who say it would decrease, and others who say it would stay the same. Explain it with ice in a glass. I still think water level will stay the same. Using density of water solid and liquid i get that 90 percent of the ice will be submerged and 10% above water line. However, liquid water is 10% more dense than solid water. I want to say that the 10% of ice above the water level compensates to exactly equal the 10% difference in volumes of liquid and solid water. Am I wrong??? I am starting to wonder, and I may be wrong. I just want to understand and if im right to be able to explain it better.

Tonight I was talking with a friend. Long story short: I said that when an iceberg melts, the water level will be the same before and after. He said he dont buy it because most of the iceberg is below the surface of the water and solid water takes up more volume than liquid water. He thinks that water levels will decrease. I couldnt figure out a good way to explain to him why this is not true. It is just something I THOUGHT i always knew. After searching the internet, I have found many scientists who say water levels would increase, some who say it would decrease, and others who say it would stay the same. Explain it with ice in a glass. I still think water level will stay the same. Using density of water solid and liquid i get that 90 percent of the ice will be submerged and 10% above water line. However, liquid water is 10% more dense than solid water. I want to say that the 10% of ice above the water level compensates to exactly equal the 10% difference in volumes of liquid and solid water. Am I wrong??? I am starting to wonder, and I may be wrong. I just want to understand and if im right to be able to explain it better.
No, you're exactly right. When something floats, it displaces a volume of water which is the volume of water that would be needed to get a mass equal to the floating object. If an icebrg is floating, there should be no effect on the volume of the water level after it melts, apart from a teeny tiny difference in the volume of water at 0 C vs 5 C. But assuming that you've got ice water at 0 degrees in equilibrium with floating ice, and if just enough energy was added to the system to make the ice melt while keeping he temperature at 0 degrees, then the water level should remain unchanged.

Biology question not related to the MCAT..........

Why does milk calm the stomach down when you have an upset stomach??? Does it have something that is basic in it to counter the acidity???

Biology question not related to the MCAT..........

Why does milk calm the stomach down when you have an upset stomach??? Does it have something that is basic in it to counter the acidity???
Milk is slightly acidic, but the calcium in milk acts as a buffer. That brings up stomach pH rapidly when you drink it.

It has been suggested that this buffering effect, while it helps the short-term effects of heartburn, is bad in the long-term because the stomach should be acidic and need sto be for proper digestion. However, the site that says that is sponsored by Nexium, so I'd take that with a grain of salt (washed down with a big glass of milk, of course). I know I drink a lot of milk, but I only seem to have acid problems only when I have stress problems, and I tend to drink milk primarily with foods that are highly acidic--for instance when eating lots o' tomatoes.

Milk is slightly acidic, but the calcium in milk acts as a buffer. That brings up stomach pH rapidly when you drink it.

It has been suggested that this buffering effect, while it helps the short-term effects of heartburn, is bad in the long-term because the stomach should be acidic and need sto be for proper digestion. However, the site that says that is sponsored by Nexium, so I'd take that with a grain of salt (washed down with a big glass of milk, of course). I know I drink a lot of milk, but I only seem to have acid problems only when I have stress problems, and I tend to drink milk primarily with foods that are highly acidic--for instance when eating lots o' tomatoes.

I'd be careful.

It's not a wise idea to mix something highly acidic(like orange juice) with milk.

Instant curdling. :(

This is borderline MCAT related/non MCAT related heh. What would be the geometry of an sp7 hybridized atom, assuming no lone pairs?

This is borderline MCAT related/non MCAT related heh. What would be the geometry of an sp7 hybridized atom, assuming no lone pairs?
That has to be a typo. There are only three p-orbitals in an atom for a given principle quantum level. Beyond that, to exceed the octet, the atom will use d-orbitals if it has any available.

bump

I have a question. I'm taking a Genetics night class and we are studying chromosomal alterations, specifically uniparental disomy.

Why does non-disjunction in meiosis I create a gamete with two homologous non-identical chromosomes, while non-disjunction in meiosis II creates a gamete with identical ones? It seems like both would create a gamete with identical homologous chromosomes. What am I missing here about meiosis?

I understand that these scenarios both result in UPD, the first in heterodisomy and the second case in isodisomy, but I don't understand why the nonidentical/identical chromosome situations arise in the first place.

I have a question. I'm taking a Genetics night class and we are studying chromosomal alterations, specifically uniparental disomy.

Why does non-disjunction in meiosis I create a gamete with two homologous non-identical chromosomes, while non-disjunction in meiosis II creates a gamete with identical ones? It seems like both would create a gamete with identical homologous chromosomes. What am I missing here about meiosis?

I understand that these scenarios both result in UPD, the first in heterodisomy and the second case in isodisomy, but I don't understand why the nonidentical/identical chromosome situations arise in the first place.
It has to do with how the chromosomes separate during each stage of meiosis. Remember that in meiosis I, the homologs are being separated from each other. If there is non-disjunction, the homologs, which are not identical, stay together in the same cell. This gives rise to a cell w/ two non-identical chromosomes (assuming that the sister chromatids of each homolog separate normally during meiosis II).

After meiosis I, the homologs are in separate cells, but the chromosomes are still paired with their sister chromatids. If these don't separate in meiosis II, then the cell will have two identical copies of the chromosome b/c both copies come from the same homolog. This gives rise to a cell w/ two identical chromosomes.

If this is difficult for you to conceptualize, look at a diagram of meiosis. Pay attention to when the non-identical homologs separate from one another (during meiosis I) versus when the identical sister chromatids separate from one another (during meiosis II).

Umm, okay I think I get it.

So the second part, meiosis II, I understand--the sister chromatids are identical and if there's nondisjunction, it results in two identical chromatids in the gamete.

In meiosis I, the homologs are different (from crossing over?), and if there's nondisjunction, we'll have two homologs in the same cell. Is that right?

Thanks, Q!

Umm, okay I think I get it.

So the second part, meiosis II, I understand--the sister chromatids are identical and if there's nondisjunction, it results in two identical chromatids in the gamete.

In meiosis I, the homologs are different (from crossing over?), and if there's nondisjunction, we'll have two homologs in the same cell. Is that right?

Thanks, Q!
Even if you neglect crossing over (which I wasn't even considering in my earlier argument), the homologs will not be identical. Remember that each homolog comes from a different parent. So if we are talking about chromosome #3, for example, you have two copies of it: one from your mom, one from your dad. Since your mom and dad are not genetically identical (I hope! :eek: ), their chromosomes are also not identical. Hence, homologs are similar to each other, but are not identical. If the two homologs end up in the same gamete, they will be two similar but non-identical copies of the same chromosome.

Oh yeah! I think. Homologs are from different parents. So if I use myself as the example, if nondisjunction occurs in meiosis one, my gamete will have an extra say, chromosome 15. One from mum and one from dad, but normally, there should only be one chrom 15, from mom OR dad (but really a hybrid from crossing over). When this (#15 from my mom and dad) is passed on to my offspring, if the zygote, with three chrom 15s, gets rid of the wrong chrom 15 (the one from my wife), then we have uniparental nondisjunction, and more specifically paternal heterodisomy.

Do I have it?

Oh yeah! I think. Homologs are from different parents. So if I use myself as the example, if nondisjunction occurs in meiosis one, my gamete will have an extra say, chromosome 15. One from mum and one from dad, but normally, there should only be one chrom 15, from mom OR dad (but really a hybrid from crossing over). When this (#15 from my mom and dad) is passed on to my offspring, if the zygote, with three chrom 15s, gets rid of the wrong chrom 15 (the one from my wife), then we have uniparental nondisjunction, and more specifically paternal heterodisomy.

Do I have it?
I follow you up to the point where you talk about the zygote "getting rid" of one of the chromosomes. :confused: It is the GAMETE that is disomic if it has an extra copy of the chromosome, not the zygote. If one gamete that fused to make that zygote had two copies of chromosome 15, you are going to wind up with a zygote having trisomy 15. That assumes, of course, that an embryo with trisomy 15 is viable. I have no idea whether it is.

That assumes, of course, that an embryo with trisomy 15 is viable. I have no idea whether it is.
Complete trisomy 15 is lethal.

Complete trisomy 15 is lethal.
Thanks. I thought it might be.

I follow you up to the point where you talk about the zygote "getting rid" of one of the chromosomes. :confused: It is the GAMETE that is disomic if it has an extra copy of the chromosome, not the zygote. If one gamete that fused to make that zygote had two copies of chromosome 15, you are going to wind up with a zygote having trisomy 15. That assumes, of course, that an embryo with trisomy 15 is viable. I have no idea whether it is.
Thanks, Q. I think I got it. I was indeed talking about the zygote. The gamete is disomic, too, but after fertilization, the zygote is UNIparental disomic 15 in my example, trisomic 15 all together.

What I meant was, if the zygote were to try to "correct" itself (trisomic rescue) but instead got rid of the wrong set of chrom 15, it would create a UPD 15 offspring. I think.

Sorry, most of genetics is brand new to this former english major, so I may not have the best phrasing.

Ek's & TPR emphasize that it always requires energy to break a bond. This endogonic "breaking" of bonds pushes the reaction to the transition state. If the overall reaction is exogonic the subsequent forming of new bonds must release more energy than Ea.
I wonder about some possible implications of the breakdown of a compound into its standard state elements. Consider some compund with a positive delta G of formation. In the reserve reaction the compound will be broken down into standard state elements while freeing energy. I don't understand where this freed energy comes from as no new bonds are formed. Does the elements electron reconfiguration into its SS from the transition state free energy?

Thanks,

Ek's & TPR emphasize that it always requires energy to break a bond. This endogonic "breaking" of bonds pushes the reaction to the transition state. If the overall reaction is exogonic the subsequent forming of new bonds must release more energy than Ea.
I wonder about some possible implications of the breakdown of a compound into its standard state elements. Consider some compund with a positive delta G of formation. In the reserve reaction the compound will be broken down into standard state elements while freeing energy. I don't understand where this freed energy comes from as no new bonds are formed. Does the elements electron reconfiguration into its SS from the transition state free energy?

Thanks,
I am going to move these posts to the Questions Beyond the Scope of the MCAT thread, because this is way beyond what you need to know for the MCAT.

I am not sure about the answer to your question, but my guess is that many of these compounds with positive free energies of formation are comprised of elements that come in pairs in their standard states. For example, if you dissociate water, you don't get individual hydrogen and oxygen ATOMS; you get diatomic hydrogen and oxygen MOLECULES. So you do then have a scenario where you would be forming bonds if you reverse the reaction and convert a compound like water to its standard state elements. Maybe Dr Chandy or nutmeg will have some other ideas.

HI

I was wondering what the explanation was to a question posed a long time ago. Please explain in depth. A bubble is rising in a bucket of water or beer bottle or whatever. This tests two concepts, I'm not exactly sure what they were. One was Bernoullis equation (wheter its speed increases or decreases) ,since it is a moving fluid, and the second thing was pressure on it or something. If you know what I am referring to please explain everything. ;)

HI

I was wondering what the explanation was to a question posed a long time ago. Please explain in depth. A bubble is rising in a bucket of water or beer bottle or whatever. This tests two concepts, I'm not exactly sure what they were. One was Bernoullis equation (wheter its speed increases or decreases) ,since it is a moving fluid, and the second thing was pressure on it or something. If you know what I am referring to please explain everything. ;)

Speed of the bubble will increase
(Pressure and velocity of a fluid at a given point are inversely related according to bernoulli's principle)

Pressure on the bubble will decrease
(Pressure=dgh where d=density of water/beer, g=acceleration due to gravity, and h=depth of water/beer)

Speed of the bubble will increase
(Pressure and velocity of a fluid at a given point are inversely related according to bernoulli's principle)

Pressure on the bubble will decrease
(Pressure=dgh where d=density of water/beer, g=acceleration due to gravity, and h=depth of water/beer)


Although the pressure explanation makes sense to me the speed one does not. As the bubble rises its "height" and therefore elevation head increase so from Bernoulli's eqn. does this mean that it does not "speed up as much as it should?" A little confused, please clarify. Also, does the bubble expand as it rises because pressure decreases?

Although the pressure explanation makes sense to me the speed one does not. As the bubble rises its "height" and therefore elevation head increase so from Bernoulli's eqn. does this mean that it does not "speed up as much as it should?" A little confused, please clarify. Also, does the bubble expand as it rises because pressure decreases?

Just know that for problems which test bernoulli's concept, or where pressure and velocity of a fluid are involved, if pressure on the fluid is high, then the velocity of the fluid will be low. If pressure on the fluid is low, then the velocity of the fluid will be high.

The bubble will expand as it rises due to the pressure decrease of the surrounding fluid.

Hey there Smarties,

Today, my light-bulb went out.

I tried to stare at it to make it go back on, but it didn't work, so I went to replace it. "Say, what are these mysterioius numbers...?" If I have a 100Volt/36W resistor, (my burned out bulb), does that mean I=.36? If so, what will stop me from turning the light on for various increments of time, calculating the use of AC current in the wee hours of the morning?
I wanted to know if these equations are really applicable or if 0.36 is a bunch of pish-posh.

Keep on rockin' in the free world,
Caboose.

Hey there Smarties,

Today, my light-bulb went out.

I tried to stare at it to make it go back on, but it didn't work, so I went to replace it. "Say, what are these mysterioius numbers...?" If I have a 100Volt/36W resistor, (my burned out bulb), does that mean I=.36? If so, what will stop me from turning the light on for various increments of time, calculating the use of AC current in the wee hours of the morning?
I wanted to know if these equations are really applicable or if 0.36 is a bunch of pish-posh.

Keep on rockin' in the free world,
Caboose.
I'm assuming that you used P=IV to come to that conclusion. The only thing I'm unsure about is whether you can use that equation for AC current. If your house were wired for DC, I'd feel more confident in saying that you're right. ;) Ok, I'm sure about one thing: this will definitely NOT be on the MCAT. Moving to the Outside the Scope of the MCAT Thread. :)

OK...Big Bang Theory and 2nd Law of Thermodynamics...At the beginning of the universe, the universe was the "system"...so it had a certain level of disorder at that point. How could the disorder of the universe increase (when in fact it is the system with no "universe" to create disorder in) when all the planets had to collide, evolution etc.... :idea:

OK...Big Bang Theory and 2nd Law of Thermodynamics...At the beginning of the universe, the universe was the "system"...so it had a certain level of disorder at that point. How could the disorder of the universe increase (when in fact it is the system with no "universe" to create disorder in) when all the planets had to collide, evolution etc.... :idea:
Don't try to make sense of the Big Bang. All of our laws of the universe break down when you try to trace back to a singularity.

I keep mysteriously trying to make the lightbulb go on... I've converted to the efficient use of flourescent bulbs.
When the lightbulb goes on before April 22nd and it flutters a little when you turn it on - does that have anything to do with the phosphor coating moving it's electrons to a higher energy level? I just wondered about the enchanting flickering that occurs in the wee morning hours. Anybody wanna take the Pepsi challenge?

Caboose.

oh - thanks for the help on the MCAT section, Q. :)

Glycoproteins' sugar residues are found exclusively in the extracellular domain, yes?

If so, is there a reason for this?

Glycoproteins' sugar residues are found exclusively in the extracellular domain, yes?

If so, is there a reason for this?


Sugar residues serve as ID tags for the specific cell they are present on.
A specific cell type will have specific glycoprotein sugar residues. Sugar residues help the immune system identify self cells from non-self cells.

" ...formation of the eye, where the optic vesicles induce the ectoderm to thicken and form the lens placode, which in turn induces the optic vesicle to form the optic cup, which in turn induces the lens placode to form the cornea and the lungs."

...Seriously? The lungs?

Caboose.

p.s. Look what I found! :idea:

" ...formation of the eye, where the optic vesicles induce the ectoderm to thicken and form the lens placode, which in turn induces the optic vesicle to form the optic cup, which in turn induces the lens placode to form the cornea and the lungs."

...Seriously? The lungs?

Caboose.

p.s. Look what I found! :idea:
:laugh: You can literally see yourself breathing, I suppose.

:laugh: You can literally see yourself breathing, I suppose.
:laugh:

Caboose.

I love bio.
O.k., so Strontium is incorporated into bone better than Calcium. It makes a complex with phosphate, yeah? ...but Sr has a larger radius and is less electronegative than Ca - any thoughts on why osteoblasts would like to add that element more?
Caboose.

How does pyridinium tribromide react?

I mean I see an aromatic 6-membered ring with an N+ in it. I also see a "Br-Br=Br(-)". And then I magically see a Br(-) ionically on the N+, and a Br-Br. ??? So the ring supplies nucleophile Br, and the Br-Br supplies electrophile Br?

Not to be too harsh here, but on the subject of Organic...You know it for the MCAT & forget it for the rest of your life. I have nearly finished my M1 year and I can honestly tell you that I haven't thought about Orgo since the MCAT. I haven't taken pharm yet, but I'm almost 100% sure that you don't need it.

So if this is a question you have in your MCAT studying, stick to the basics and you will be fine.

on the subject of Organic...You know it for the MCAT & forget it for the rest of your life.
At least you try to. In both biochem and physiology this (my M1) year, instructors keep talking about the "benzene rings of steroid hormones." I haven't had the nerve to disagree.

I have a problem about finding out a chemical structure (C16H24O2).
I have an IR, H nmr, and C nmr...
I checked all over, books, websites etc. I also tried to figure it out myself of course:
IHD:5
H-nmr shifts are :1.11, 2.49, 2.70, 3.08, 5.38 (does this mean no aromatic H's??)

Would anyone be willing to take a look at 'em?? Someone with some time to kill?

I kinda have an idea but stuck at some points (with the multiplicity, symmetry parts etc.) I learned the stuff last semester and its somewhat rusty.
If anyone who's good at this want to give it a try, please let me know. I can email you the scanned paper. I would appreciate anyone's help.
I'll try different forums as well....

stressed...

I have a problem about finding out a chemical structure (C16H24O2).
I have an IR, H nmr, and C nmr...
I checked all over, books, websites etc. I also tried to figure it out myself of course:
IHD:5
H-nmr shifts are :1.11, 2.49, 2.70, 3.08, 5.38 (does this mean no aromatic H's??)

Would anyone be willing to take a look at 'em?? Someone with some time to kill?

I kinda have an idea but stuck at some points (with the multiplicity, symmetry parts etc.) I learned the stuff last semester and its somewhat rusty.
If anyone who's good at this want to give it a try, please let me know. I can email you the scanned paper. I would appreciate anyone's help.
I'll try different forums as well....

stressed...

Thank you for moving this here. I didn't even know about this forum.

H-nmr shifts are :1.11, 2.49, 2.70, 3.08, 5.38 (does this mean no aromatic H's??)


With the limited information, it's tough, but I would expect to find a fatty acid. The 5.38 is probably from the COOH at one end. The 1.11 is from CH3 at the other end. The heights og the others would help you determine if you are looking at = or - bonds in the middle. Just my best guess with limited information...

I've got a question that I've been wondering about.(Only for my own edification.) Why does cooling slowly when doing recrystallization generally work better(less garbage) than going fast? Not a big deal since I'm done with my premed course work, I was just curious.

I've got a question that I've been wondering about.(Only for my own edification.) Why does cooling slowly when doing recrystallization generally work better(less garbage) than going fast? Not a big deal since I'm done with my premed course work, I was just curious.
If you cool slowly, the molecules will selectively prefer to surround themselves with similar molecules (other product molecules) to form a regular lattice that tends to exclude the differently-shaped impurities. On the other hand, if you precipitate the product quickly, the impurities tend to crash out of solution along with the product, and they become incorporated into your crystal because the crystals form too quickly for selective lattice formation to occur.

If you cool slowly, the molecules will selectively prefer to surround themselves with similar molecules (other product molecules) to form a regular lattice that tends to exclude the differently-shaped impurities. On the other hand, if you precipitate the product quickly, the impurities tend to crash out of solution along with the product, and they become incorporated into your crystal because the crystals form too quickly for selective lattice formation to occur.

Geez, I should have known that already. I mean they kind of covered that on the sugar episode of Good Eats. :) Thanks Q

If presynaptic neuron is placed closed to axon, which way would AP (if any AP is produced) proceed? I believe AP in axon can travel in both directions so what would determine the direction in which the AP will proceed?
AP in axon travel because of the depolarization of Na+ channels in axon, right? So if presynaptic neuron was placed near an axon and it secretes NT that will open Na+ voltage gated channels, AP will occur. So what direction?

Thank you for your help in advance.

I'm not sure if I completely understand your question but I'll take a stab at it. If an action potential is high enough, meaning the NTs activate the ligand gated channels. The action potential always travels along the axon to the synapse, whether the synapse is a neuromuscular junction or another neuron. The AP cannot travel backwards because the ion channels have a brief inactivation period where the cannot be repolarized hence an intrinsic directionality in AP. I hope this helps.

I'm not sure if I completely understand your question but I'll take a stab at it. If an action potential is high enough, meaning the NTs activate the ligand gated channels. The action potential always travels along the axon to the synapse, whether the synapse is a neuromuscular junction or another neuron. The AP cannot travel backwards because the ion channels have a brief inactivation period where the cannot be repolarized hence an intrinsic directionality in AP. I hope this helps.

You are right. If a certain threshold is met, than a action potential will travel down the axon hillock to the synapse where calcium influx will lead to the release of neurotransmitter. The threshold, usually about -50mv, is a all or nothing response--meaning, if it is met than a action potential will be generated.

how could we explain the irritation in the eyes after swimming in the sea? how would an eye drom ease this particular irritation?

well, there is this article on JACS(08/02/2006) about the new technique of introducing small oligonucleotides into cell by linking 15-20mers with cationic peptides(variable repetition of KKKR repeats).

i was wondering what are the common non-viral protocols that are currently used to put siRNA/miRNA into cells.

If you are wondering about stuff like siRNA/miRNA then I suggest you GET A NEW HOBBY!!!

Of course I am just kidding & also of course, I have no clue about that.

If you are wondering about stuff like siRNA/miRNA then I suggest you GET A NEW HOBBY!!!

Of course I am just kidding & also of course, I have no clue about that.

just wondering how much this new protocol is better than traditional cationic non-viral vectors(so called "proton sponge").

I'm sure we all know about Maxwell's Demon, that impish little fellow who has the ability to allow faster moving molecules to pass through the trap-door he controls so as to effect a temperature change between two chambers that are initially at the same temperature. In so doing, the demon would apparently violate the Second Law of Thermodynamics. The Demon thus presents a paradox.

The paradox needs to be explained, ideally within the context of Thermodynamics. The fact that JC Maxwell came up with the paradox should make us take the paradox seriously. He (along with W. Gibbs) were the geniuses who developed Thermodynamics.

It's easy to dismiss the paradox by saying that the Demon can't exist or can't do what he's supposed to do for various reasons. For example, some have argued that the Demon would need to have unaccounted-for energy he is not allowed to have to do what is expected of him, and others have argued that quantum uncertainties make his task impossible.

Unfortunately, these explanations for the impossibility of the Demon use arguments outside of Thermodynamics. They may or may not be correct, but I find them unsatisfying because they require arguments outside of Thermodynamics.

If you stay within classical Thermodynamics, I think that it is possible to accept that the Demon can do what Maxwell said he could, without violating the Second Law...

One way to accept the Demon would be to posit that for him to be able to do what he needs to do, he would need to be internally complex. One would need to calculate his complexity into the calculation of the entropy of the system in which he operates. If we do this calculation, I think that the Demon could do what Maxwell suggested (i.e. cause a temperature change in the chambers), but only to the degree that the Demon's complexity (his negative entropic value) allowed. No "violation" of the Second Law need occur, and no need to refer to any extra-Thermodynamic explanations. I think JCM would have appreciated this approach.

Any comments from you Physicists out there?

Here's a question for all you chemists out there. Are nitrogen molecules really smaller than oxygen molecules? I ask because my brother was watching some show on tinkering with your car and they said that was true. But from what I remember even though oxygen atoms are smaller the difference isn't much. Further more N2 forms a triple bond and O2 a double so I'd expect nitrogen molecules to actually be smaller.(Sounded like a lot of snake oil to me but what do I know.)

Here's a question for all you chemists out there. Are nitrogen molecules really smaller than oxygen molecules? I ask because my brother was watching some show on tinkering with your car and they said that was true. But from what I remember even though oxygen atoms are smaller the difference isn't much. Further more N2 forms a triple bond and O2 a double so I'd expect nitrogen molecules to actually be smaller.(Sounded like a lot of snake oil to me but what do I know.)
I'm pretty sure that oxygen molecules are still smaller than nitrogen molecules in spite of only having a double bond. That's why you don't hear about people filling their tires with oxygen; the oxygen molecules would leak out of the tires faster than the nitrogen molecules do. Here's an article that backs me up, although admittedly it's from a lay source: http://www.cbc.ca/story/news/national/2006/08/22/nitro-tires.html

I'm pretty sure that oxygen molecules are still smaller than nitrogen molecules in spite of only having a double bond. That's why you don't hear about people filling their tires with oxygen; the oxygen molecules would leak out of the tires faster than the nitrogen molecules do. Here's an article that backs me up, although admittedly it's from a lay source: http://www.cbc.ca/story/news/national/2006/08/22/nitro-tires.html

Actually I looked into this a bit more and you're correct. What I found out is that the b in that "Vander Waals" equation corresponds to the size of the molecules. Oxygen's b is smaller than nitrogen's b, not by much but it's smaller. So oxygen really is smaller and would diffuse a bit faster.(I'm still surprised by this result but I really don't have an intuitive sense how big an atom is or how big a bond is relative to an atom.) Still, I've never really noticed my tires leaking pressure that fast and I use air. I mean I doubt I refill them more than once a month. Still I can think of a better reason not to fill your tires with oxygen:D (BOOMA BOOMA) Anyway thanks for answering that one Q.

Dave_D,

When you are using 'air' to fill your tires I think you are fogetting the composition of air that you are using which is approximately 78% Nitrogen & 20% Oxygen. Nitrogen is the most abdunant molecule in our atmosphere & all those machines are doing is compressing the air. I do not believe that this changes the composition at all so you are still filling your tires mostly w/ Nitrogen.

Actually I looked into this a bit more and you're correct. What I found out is that the b in that "Vander Waals" equation corresponds to the size of the molecules. Oxygen's b is smaller than nitrogen's b, not by much but it's smaller. So oxygen really is smaller and would diffuse a bit faster.(I'm still surprised by this result but I really don't have an intuitive sense how big an atom is or how big a bond is relative to an atom.) Still, I've never really noticed my tires leaking pressure that fast and I use air. I mean I doubt I refill them more than once a month. Still I can think of a better reason not to fill your tires with oxygen:D (BOOMA BOOMA) Anyway thanks for answering that one Q.
I was kind of surprised to see that it makes such a big difference also, not because of the size difference between the molecules being small, but because air is mainly composed of nitrogen (78% nitrogen versus 21% oxygen). Apparently if you live in Winnipeg, though, that 21% is enough to make a difference. ;)

Dave_D,

When you are using 'air' to fill your tires I think you are fogetting the composition of air that you are using which is approximately 78% Nitrogen & 20% Oxygen. Nitrogen is the most abdunant molecule in our atmosphere & all those machines are doing is compressing the air. I do not believe that this changes the composition at all so you are still filling your tires mostly w/ Nitrogen.

Well I knew air was mostly nitrogen. The thing is that people sometimes fill their tires with nitrogen instead of air for some alleged benefit. Yet the main reason they give, IE gas diffusing out of the tires, I've never noticed this being a problem with my own tires and I use air.

I was kind of surprised to see that it makes such a big difference also, not because of the size difference between the molecules being small, but because air is mainly composed of nitrogen (78% nitrogen versus 21% oxygen). Apparently if you live in Winnipeg, though, that 21% is enough to make a difference. ;)

Ok, so I guess you're not buying it much either. Actually the only person I've ever remembered having problems with tires holding pressure was my mom and it went away when she got new tires.(Her old ones were starting to go bald.) It just sounded like some people who tinker with their cars too much that justified it with some scientific sounding mumbo-jumbo. I guess I could check "The straight dope" and see if they've done anything on it.

Ok, so I guess you're not buying it much either. Actually the only person I've ever remembered having problems with tires holding pressure was my mom and it went away when she got new tires.(Her old ones were starting to go bald.) It just sounded like some people who tinker with their cars too much that justified it with some scientific sounding mumbo-jumbo. I guess I could check "The straight dope" and see if they've done anything on it.
I wonder if it has anything to do with climate. Gases compress a lot due to decrease in temperature (Charles's Law :)) I'm from FL, and I'd never heard of using nitrogen to fill your tires until you brought up this question. It just isn't an issue here because it basically doesn't ever get cold here. I can't even tell you the last time I had to fill my tires; usually they just check the pressure when I get my oil changed every four months and they leave well enough alone. You're from MA, so you could have some issues due to temperature swings, but no doubt the changes you get are nowhere near as severe as the kind of climate they have in Winnipeg.

Formula 1 cars use Nitrogen in their tires because they heat up faster. At least that's what the race people say...

Anyways, I bet you could have nearly 100% N2 in your tires with just using compressed air. The first set will have 70% N2. Then as Oxygen diffuses out faster, you put in more compressed air. So the volume of new "displacing" air is 70% N2 instead of 0% N2 that left (I'm doing net out, which is the diff between O2 and N2 out). So each time you refill your tires with just a little more air, you're adding more N2.

I'm not sure if this is the case for me, but it's possible. When I bought my car new, I'd refill the tires literally about once every 1 or 2 months (I drove it 3,500 miles a year). Last time I filled my tires was back in April, 3 years after I had my car from new with the original tires (only 9,000 miles at that time). Still the same air in my tires, but they're not as deflated as they used to be 5 months later. Although I haven't driven as much recent since this test last Saturday. Driving probably makes you lose more air, too.

Edit: Maybe since it's been pretty constant temp here in Orlando for the last 5 months has kept the pressure the same? Another factor.

I wonder if it has anything to do with climate. Gases compress a lot due to decrease in temperature (Charles's Law :)) I'm from FL, and I'd never heard of using nitrogen to fill your tires until you brought up this question. It just isn't an issue here because it basically doesn't ever get cold here. I can't even tell you the last time I had to fill my tires; usually they just check the pressure when I get my oil changed every four months and they leave well enough alone. You're from MA, so you could have some issues due to temperature swings, but no doubt the changes you get are nowhere near as severe as the kind of climate they have in Winnipeg.

My friend gets Nitrogen filled in his tires from Costco here in Orlando. :thumbup:

My friend gets Nitrogen filled in his tires from Costco here in Orlando. :thumbup:
Dude, they sell beach sand to tourists in Orlando. :meanie: I wouldn't judge the rest of the state based on what they do in Orlando. :p

Dude, they sell beach sand to tourists in Orlando. :meanie: I wouldn't judge the rest of the state based on what they do in Orlando. :p

True! :laugh: :p

My friend gets Nitrogen filled in his tires from Costco here in Orlando. :thumbup:


they do it around here too... i think Bell Tire does it... it sounds like a bull**** promotional ploy

they do it around here too... i think Bell Tire does it... it sounds like a bull**** promotional ploy

It was free, but I would never pay for it either if they charged. Can't say I care enough for it.

Anyways, I bet you could have nearly 100% N2 in your tires with just using compressed air. The first set will have 70% N2. Then as Oxygen diffuses out faster, you put in more compressed air. So the volume of new "displacing" air is 70% N2 instead of 0% N2 that left (I'm doing net out, which is the diff between O2 and N2 out). So each time you refill your tires with just a little more air, you're adding more N2.


Actually I just realized you're on to something. If diffusion is an issue (like they claim it is.) then they're missing a piece of the puzzle. Diffusion goes from regions of high concentration to low. So if you were to fill your tires with nitrogen O2 should diffuse in until equilibrium is reached and that would be the same level if you added extra O2 and let it diffuse out. So if we do like you suggest I'd expect O2 levels to be the same after a while in the air filed vs. nitrogen filled tires.(Of course if diffusion isn't a big deal then of course there'd be a difference in gas composition in the air vs. N2 filled tires but then the whole point of doing N2 goes away.)

I'm guessing that F1 teams actually have a real reason but for the average person it's pointless.(It might be as simple as a compressor might break at the wrong time but a bunch of gas cylinders rarely do.)

This is a relativity problem, I'm supposed to start by finding the velocity, but i'm not sure if I use the earth's circumference as the distance for the v=d/t...ok here's the problem:

A clock is placed in a satellite that orbits the earth with a period of 119 min. By what time interval (in seconds) will this clock differ from an identical clock on earth after 1 y? (Assume that special relativity applies and neglect general relativity.)

Any help would be greatly appreciated, thanks!

How come cysteine is polar, but hydrophobic? I thought polar molecules are always hydrophilic? thanks!

"[This] study has shown that free cysteine (Cys_SH) residues, as well as disulfide-bonding cystines (Cys_SS), behave like strongly hydrophobic residues in proteins. This apparent hydrophobic nature of Cys_SH seems to conflict with the polarized nature of the sulfhydryl group. However, we need to consider the fact that the sulfhydryl group is inactive toward water molecules. More specifically, unlike the hydroxyl group (-OH), the sulfhydryl group (-SH) has essentially no ability to form a hydrogen bond with water. This may explain why the -SH group is both active in metal binding and disulfide bond formation, and is hydrophobic in water."

From Strong hydrophobic nature of cysteine residues in proteins (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T36-3XB0N6H-H&_coverDate=09/10/1999&_alid=241945989&_rdoc=1&_fmt=&_orig=search&_qd=1&_cdi=4938&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=3cb10a335716303532fc517906a12b3a) by Nagano, Ota, and Nishikawa.

bump

Aw... I'm so disappointed that this thread seems to have died.

Comments about the nitrogen-filled tires: I did plenty of research to confirm the following: it's BS. The decreased rate of effusion of nitrogen is nowhere near worth the expense, if there is expense. (More on this later.) Other oft-cited rationales: different heating characteristics (total BS); reduced tendency to oxidize tires (irrelevant if you actually use your tires, because they'll wear out long before it matters); decreased flammability (apparently confusing compressed air with compressed oxygen).

What it comes down to is that compressed nitrogen is available cheap (in big quantities), at high pressures; also, the separation process dries it. Compressed air is much harder to get, partly because the presence of water in it tends to rust the inside of steel containers (just ask a scuba diver). For a Formula One team, it's far easier to use tanks of whatever-the-heck than to have a compressor; the cheapest whatever-the-heck is nitrogen. The stuff they spout about more consistent heating? Who knows, they may believe it, but it's utter tripe.

Aircraft also use nitrogen, because their tires are inflated to high enough pressures that it's impractical for them to use anything other than bottled gas. Again, nitrogen's the cheapest option.

This is a relativity problem, I'm supposed to start by finding the velocity, but i'm not sure if I use the earth's circumference as the distance for the v=d/t...ok here's the problem:

A clock is placed in a satellite that orbits the earth with a period of 119 min. By what time interval (in seconds) will this clock differ from an identical clock on earth after 1 y? (Assume that special relativity applies and neglect general relativity.)
First, solve for v. It's not OK to use Earth's radius; the altitude is such that the centripetal force mv^2/r is equal to the gravitational force GMm/r^2. Use 119 x 60 x v = 2(pi)r to get r = about 1200v, then plug that back in. I get v = about 7000 m/s, though I could easily be off.

Then, time is dilated by the Lorenz factor, square root of (1 - v^2/c^2), or about .9999999995. The change is a factor of around 5e(-10). A year has somewhat over 30,000,000 seconds, so I think your clock will be slow by something on the order of 0.001 seconds.

That's the I-can't-find-a-pencil, I refuse to use a calculator version. Am I at all close?

First, solve for v. It's not OK to use Earth's radius; the altitude is such that the centripetal force mv^2/r is equal to the gravitational force GMm/r^2. Use 119 x 60 x v = 2(pi)r to get r = about 1200v, then plug that back in. I get v = about 7000 m/s, though I could easily be off.

Then, time is dilated by the Lorenz factor, square root of (1 - v^2/c^2), or about .9999999995. The change is a factor of around 5e(-10). A year has somewhat over 30,000,000 seconds, so I think your clock will be slow by something on the order of 0.001 seconds.

That's the I-can't-find-a-pencil, I refuse to use a calculator version. Am I at all close?

That sounds right.

I read that in atomic hydrogen with empty 2s, 2px, 2py, and 2pz orbitals, these are all degenerate. Why would this be? it seems like the lower energy of hybridized sp orbitals would not compensate for the increase in 2s without more electrons (like even at least one p electron).

thanks

Comments about the nitrogen-filled tires: I did plenty of research to confirm the following: it's BS. The decreased rate of effusion of nitrogen is nowhere near worth the expense, if there is expense. (More on this later.) Other oft-cited rationales: different heating characteristics (total BS);

Actually there would be different heating characteristics between pure N2 vs N2+O2, but it is probably negligible. N2 requires greater heat input (1.039 kJ/kg*K) to increase 1 degree than O2 (.915 kJ/kg*K). Since PV=nRT, the tire pressure would have greater consitancy as the tire heated up than with air, and we all know tire pressure is very important in contact area and suspension dynamics.

decreased flammability (apparently confusing compressed air with compressed oxygen).

No O2=no explosion (compressed air has 20% O2 in it).

I have an even more far fetched reason: mass. N2 weighs less than air. If you have ever held an F1 wheel and tire, they are super light (but not because of the gas difference).

Okay, so these aren't really "advanced" biology Qs, but merely Qs that came to mind as I was reviewing information on the endocrine system. I'm not in school right now (self-study), so hopefully someone can help out!

1. If a deficiency in insulin results in diabetes, can an excess of glucagon also result in diabetes? (I.e. if there is a chronic excess of glucagon that results in chronically high blood sugar levels, can that "overwhelm" insulin production, in a sense?)

2. Is Addison's Disease the result of a deficiency in glucocorticoids, mineralocorticoids, or gonadocorticoids? (i.e. which one(s)?)

3. Relatedly, is Cushing's disease caused by a deficiency in glucocorticoids, mineralocorticoids, or gonadocorticoids? (i.e. which one(s)?)

4. An excess of insulin or a deficiency of glucagon both result in hypoglycemia. However, the former can also be described as "insulin shock". Is there an analogous alternate term describing the latter?

5. What are the effects of excess cholecystokinin? (And what are the effects of a deficiency in cholecystokinin?)


Thanks in advance!

1. If a deficiency in insulin results in diabetes, can an excess of glucagon also result in diabetes? (I.e. if there is a chronic excess of glucagon that results in chronically high blood sugar levels, can that "overwhelm" insulin production, in a sense?)

"Real World" Diabetes can be due to two things: 1) insulin deficiency; and, 2) insulin resisitance. Glucagon will increase blood glucose levels, but that in itself will not vreate diabetes.

2. Is Addison's Disease the result of a deficiency in glucocorticoids, mineralocorticoids, or gonadocorticoids? (i.e. which one(s)?)

Glucocorticoids

3. Relatedly, is Cushing's disease caused by a deficiency in glucocorticoids, mineralocorticoids, or gonadocorticoids? (i.e. which one(s)?)

Too much (not deficiency of) glucocorticoids

4. An excess of insulin or a deficiency of glucagon both result in hypoglycemia. However, the former can also be described as "insulin shock". Is there an analogous alternate term describing the latter?

"Hypoglucagonergic hypoglycemia" might work...

5. What are the effects of excess cholecystokinin? (And what are the effects of a deficiency in cholecystokinin?)

Don't know. Maybe some problems with pancreatic and gall bladder function


Thanks in advance!

See above inserts.

Actually there would be different heating characteristics between pure N2 vs N2+O2, but it is probably negligible. N2 requires greater heat input (1.039 kJ/kg*K) to increase 1 degree than O2 (.915 kJ/kg*K). Since PV=nRT, the tire pressure would have greater consitancy as the tire heated up than with air, and we all know tire pressure is very important in contact area and suspension dynamics.
Actually, check your math. As you point out below, nitrogen is slightly lighter than oxygen, while as you point out here, nitrogen requires greater heat per unit mass. This works out to have nitrogen's and oxygen's heat capacity per unit volume, which is what's relevant here, within 1% of each other.

No O2=no explosion (compressed air has 20% O2 in it).
Do you read a lot about explosions resulting from combustion involving compressed air? I'm thinking not.

I have an even more far fetched reason: mass. N2 weighs less than air. If you have ever held an F1 wheel and tire, they are super light (but not because of the gas difference).
That's actually less far-fetched than the others, but it's still pretty silly. F1 tires are probably inflated to a gauge pressure of about 3atm, and so might contain something on the order of 20 moles of gas. But the resulting difference of 80 grams doesn't mean what you think -- Formula One cars must meet a certain minimum weight, so the savings comes only in potential change in the ratio of sprung to unsprung weight, plus a negligible change in the rotational inertia.

No, I think I'm going with my original interpretation that it's all BS.

Actually, check your math.

If you read my original post, I said the difference was probably negligible. You just took the time to calculate it out and proved my assumption correct.

If you read my original post, I said the difference was probably negligible. You just took the time to calculate it out and proved my assumption correct.
I did read your post; I think you're being disingenuous now. You gave the values for heat per kg, not heat per mole, because you, uh, wanted to emphasize, uh, ... say, you think maybe you forgot that the relevant value was per mole (and per unit volume)? When you said "N2 requires greater heat input than O2," the numbers you gave there weren't meant to suggest that the difference was 14%, as it appeared to be -- you figured everyone would realize that those numbers you gave were actually misleading, and that the real difference was about 0.65%, even when contrasting against pure oxygen (and therefore about a tenth of a percent for air)? When you said "the tire pressure would have greater consitancy as the tire heated up than with air, and we all know tire pressure is very important," you really meant that the tire pressure wouldn't have greater consistency?

Yes, you said it was probably a negligible effect. Every word was right, except the "probably." But the thrust of your post was that there might actually be some difference.

But you're right: I just did the math you should have done and proved that you were correct. Uh-huh.

I did read your post; I think you're being disingenuous now....When you said "N2 requires greater heat input than O2," the numbers you gave there weren't meant to suggest that the difference was 14%, as it appeared to be -- you figured everyone would realize that those numbers you gave were actually misleading, and that the real difference was about 0.65%, even when contrasting against pure oxygen (and therefore about a tenth of a percent for air)?

I am not being disingenuous. All of my statements were correct. I just gave some numbers that I had easily accessible to me for illustration. The heating characteristics ARE different between N2 and air, but as I originally said without crunching the numbers they are probably negligible. I'm typically not going to waste my time calculating out something if I believe it to be a secondary effect, but to appease you, I went ahead and did the calculation, and the difference at 100 F between the specific heat on a molar basis at constant pressure for air (not 02) and N2 is 0.4%.

Yes, you said it was probably a negligible effect. Every word was right, except the "probably." But the thrust of your post was that there might actually be some difference.

Why would I start my post with a statement saying that all the numbers I am giving below probably have no effect if I didn't mean it? I was sincere in my original statement, and I think you are reading too much into this.

Well might as well bump this one with a new question. (BTW, Cecil answered my nitrogen question:D ) Anyway I was listening to people talk about CocaCola and this and that about how many issues are caused when sweetened with high fructose corn syrup vs sucrose. Anyway from my orgo class I learned enough that I figured that an acid would probably catalyze the hydrolysis of sucrose so it probably doesn't matter which they use. (I have found on line articles that do infact state this.) So quick question, suppose I went into a store and bought a bottle of Coke or Pepsi at room temperature and it was originally sweetened with succose. If I were to test it would I find it fairly close to equilibrium with regards to the equation

sucrose <-> fructose + glucose

or would I still find significant amounts of sucrose?(If I knew some of the numbers like the concentration of the sugar and the pH I could probably figure it out.)

Heres to hoping that this thread is still alive.

The question reads: the different isotypes of immunologlobin are identified based on their?

a) variable region
b) heavy chain constant region
c) light chain constant region

My textbook says "constant region", but I am thinking the answer is C, because to me, to have it on the heavy chain would be of no use.

Heres to hoping that this thread is still alive.

The question reads: the different isotypes of immunologlobin are identified based on their?

a) variable region
b) heavy chain constant region
c) light chain constant region

My textbook says "constant region", but I am thinking the answer is C, because to me, to have it on the heavy chain would be of no use.

According to this wiki article the answer is B
Short thing on isotypes (http://en.wikipedia.org/wiki/Isotype_%28immunology%29)

Anybody know more about this?(I'm seeing that there's only 2 types of light chains but 5 types of heavy.)

Heavy chains have an antigen-binding region, Fab (arms of the Y) as do light chains, but also have an Fc (base of the Y) region that corresponds to the non-antigen-specific functionality of the immunoglobulin molecule. There are five types: gamma, delta, alpha, mu, and epsilon. The five isotypes of antibodies each have the matching heavy chain: IgG, IgD, IgA, IgM, IgE. They each have a different immunologic function.
IgG: Uses its Fc region to opsonize pathogens for phagocytosis and activate the complement pathway.
IgD: Not very important or well-understood.
IgA: Fc region forms dimer, active in mucosal secretions
IgM: Expressed on surface of B cells and also secreted as the earliest specific response to an antigen (production of IgM doesn't require helper T-cell activity to switch to the other types)
IgE: Fc region attaches to receptor on mast cells; antigen binding causes mast cell degranulation -> inflammation. Classic allergic reaction is IgE mediated.