April MCAT review thread

[Shredder]

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I'm starting this thread to avoid forgetting information in these last few weeks. If you will, please post a fact that you think has a good chance of showing up on the April test, and perhaps something that is easily forgettable and needs refreshing. If no one posts, oh well, this is better than studying for my test tomorrow. If they do, it could be a decent review, better than crap Princeton anyway. I'll start:

For a capacitor, C=EA/d, where E(epsilon) is the dielectric coefficient (i think air/vacuum? is 1 and everything else is greater), A is area of plates, and d is distance separating plates. A key point is that smaller distance->greater C.

 

[BaylorGuy]

I always forget that one...here's another one. n=c/v....perhaps a relation question to how fast light travels through various mediums. One thing to remember though, frequency of the incident light is always constant.

On a side note, finished 3R and got a 33. I've got 5R, 6R, 7R, and 8 lined up before test day.

 

[medicomel]

E = hf - hfT

where fT is the threshold frequency

 

[cfdavid]

Leaving off from a previous poster that indicated that the frequency of a light ray remains the same when traveling through different media (i.e. air through water or glass), it's also good to know that, though the frequency remains the same, the wavelenth will change.

If the light ray goes from a small to larger index of refraction, the wavelenth will decrease, and vice-versa.

A way to remember this is that v=freq*wavelength. So, when a beam of light traveling in the air (index of refraction=1) then travels through glass or water(index of refraction >1), it makes sense that it would 'slow down'. So, if it slows down, but frequency must remain constant, the wavelenth must decrease.

Also, remember that chromatic dispersion is when the visible spectrum (white light) 'shines' through a glass prism. The highest frequency of all the colors is Violet (ROY G BIV), and it will bend the hardest, while Red bends the least amount.

In regards to the above, I just wanted to relate it to what the other person started off with.

I've been out of college for a while, so I've had to sort of reteach myself much of the basics, so forgive me if the below seems elementary.

I can just see the MCAT question that says, 'a student starts with a stock solution of 10M HCl' 'What volume of stock solution must he/she use to make 250mL of 0.5M HCl'?

A quick time saver worth memorizing is Mconc.*Vconc.=Mdilute*Vdilute

So, the answer to the above would be 12.5 mL of the concentrated stock solution would be needed. However, remember that the goal is to get 250mL of the correct (0.5M) molarity. So, you must add 250-12.5= approx. 237mL of water.

We can all see the question, perhaps asked instead of how much concentrated acid is needed, but rather, 'how much water must be added to make 250mL of 0.5M HCl. But, the Mc*Vc=Md*Vd will get you there. Just remember that you need to dilute it with water to make up to whatever diluted volume is asked/required.

***Don't get trapped by the Oh, sh.it, what did I just do to the Molarity after I added all that water. Remember that, the 12.5mL is 12.5mL of the concentrated stock solution (10M). So, you MUST add the water to get the diluted 0.5M solution.

I hope this helps. Once again, good thread. We can learn both by reading AND writing.

 

[cfdavid]

One more topic that I found I needed to dig a little deeper into is that of titrations. Again, I always like to put things into more simple terms.

First, I don't think that many of the review books do well to explain equivalence point very well. But the bottom line is that it's the point at which an equal number of moles of acid or base, is added to the unknown acid or base. That's how we can accomplish the goal behind the titration in the first place, which is to determine the concentration of the unknown solution (but it's easy to know what volume the unknown is since we just put it in a beaker).

So, if we have some unknown concentration of an organic acid that we found sitting in some jar in a lab (that may or may not dissociate completely), we would add a strong base such as KOH. The strong OH- simply pulls off all the Hydrogens regardless of acid strength.

Remember that Acid + Base = Salt and Water. Thus, if the salt is one of weak conjugates that don't impact pH, then essentially the only thing left in the solution to impact pH is water. Thus, in the case of HCl and KOH (strong acid and strong base), the salt is NaCl which doesn't impact pH. Therefore, the equivalence point will be at 7.

But, if you react NaOH with Acetic Acid (weak organic acid - as most organic acids are weak in relation to the stonger inorganic acids of HCl and HNO3), you will still get the 'salt' and water as products, but the conjugate base of acetic acid (acetate) DOES impact pH a bit as it's a weak base. So, the products are then Na+/Acetate- (the salt) and ofcourse Water. But, the acetate anion, being slightly basic will impact pH a bit, making the equivalence point (where all the acid and base forms the salt and water) slightly basic. So, on a titration curve of a weak acid with a strong base, look for the pH at the equivalence point to be greater than 7.

The same goes for titrating a weak base with a strong acid. The pH at equivalence point will be less than 7 (slightly acidic). I think this could garnish a few points on the MCAT.

I hope this helps a bit for anyone that's been away from gen. chem for awhile, or like I said, just never had this stuff explained very well.

 

[LT2]

another thing to remember about waves is the spectrum according to wavelength:
Radio-Micro-Infared-Visible-UV-Xray-Gamma

something very politically incorrect and in poor form, but a way to remember this by (please don't flame me, i didn't make it up, and i'm only trying to help):

Ronald - Mcdonald - Is - Very - Ugly and - Xtremely - Gay

for chemistry, know your acid/base chemistry, common ion problems and the difference between molarity, molality and normality, these make good free standing questions!

for physics, i don't remember much on optics or electricity. a lot of conceptual newtonian mechanics and wave stuff.

hope this helps! good luck!

 

[cfdavid]

In EK physics, there's a picture of a guy standing on land while looking at the image of a fish in the water. It shows how the light rays (eminating from the fish) bend away from the normal as they enter the air. So, the guy thinks he's looking at the fish, but in reality, due to how light bends when traveling through different media, he's looking at the image of the fish, which is behind the real thing.

It reminds me of when I was a kid and used to try shooting the fish in my grandpa's lake with my bee-bee gun. I would always miss, even when I was sure I had it 'locked' in.

Well, if I had known simple optics when I was 10, I would have aimed in front of the damn thing.

 

[Shredder]

Titrations: pH=pKa at the point halfway to the equivalence point. By the H-H equation pH=pKa+log[Base/Acid], so this also is the point where the concentrations of the acid/base is equal to its conjugate base/acid, meaning log[1]=0. I believe indicators are chosen based on the proximity of their color changes to the equivalence point.

Light: sin(critical angle)=n2/n1, and you know n1>n2 because sinx<=1. At any angles of incidence greater than the critical angle, there will be total internal reflection. You cannot have total internal reflection if the light is going from a faster to slower medium, only slower to faster, like water or diamond to air. Remember, angle of incidence is measured with respect to the normal to the interface, not parallel to the interface.

Endocrinology: all I could muster to remember pituitary hormones is FLATPG for anterior, and OA (orientation advisor at my college) for the Puny Posterior which only has two. The bad thing is that probably at most one question of this nature would show up on the whole test, but it seems to be consistently asked.

Collisions: momentum is always conserved. Only in (perfectly) elastic is kinetic energy conserved. Deformation, stickiness, or friction could be exceptions to this but aren't likely to appear. This seems to show up a lot.

Redox: RED CAT-reduction always happens at the cathode. AN OX-oxidation always at the anode. However, whether the charge is positive or negative on each electrode is reversed when you change from a galvanic/voltaic (spontaneous) cell to an electrolytic (needs a battery, used for plating) cell. I believe all I have posted is correct, but props to anyone who calls me out on errors.

 

[BaylorGuy]

Regarding titrations....i always messed up on the weak acid/strong base and weak base/strong acid....however, after thinking about it for a while, i came up with a good solution. As already stated Equivalence point of SA and SB equals 7. Titrate WA with SB...the SB will dissociate more than the weak acid, thus at the equivalence point, more base will be in solution than acid (thus more OH), then causing equivalence point to be greater than 7. Same thing applies to SA and WB, only opposite. At equivalence, more acid is dissociated, thus more H, thus decrease in PH, thus the equivalence point benig smaller than 7.

Momentum: Perfectly Elastic collision--momentum and Kinetic energy conserved (problem will most likely have 2 unknowns...thus use 2 equations, momentum and KE). Inelastic collision--momentum conserved (Problem will have 1 unknown...momentum)

Redox: Galvanic cell--OxidAtion occurs at Anode. anode is also negative pole. ReduCtion occurs at cathode. Ca+hode is positive pole. This reaction occurs spontaneously, thus emf is negative.
Electrolytic...same thing occurs, only anode is positive pole, cathode is negative pole. Rxn is non-spontaneous, emf is positive.

Circuits: Series--resistors add up...current is constant for ALL resistors, voltage is not
Parallel--resistors are inversely added...Voltage is constant for ALL resistors, current is not.

 

[laya533]

Lets talk a little about evolution:
homologous structures are those that are simmilar in structure and share a common origin. analogous structure is the one that share a common function but differ in origin. vestigial structures are those that have lost their ancestoral function(remnants)

stabilizing selection maintains well adopted uniform character(eliminates extremes).directional selection during a change in environment favors of extreme.disruptive selection favors both phenotypic extremes over the intermrdiate and creats polymorphism .

adaptive radiation is creation of a # of lineage from same ansector

microspheres are protein droplets.
coacervates are colloidal droplets (protein, caccharide, nucleic acid)

 

[kalix]

E = hf - hfT

where fT is the threshold frequency

that peanut face icon you have.....is weird/freaky, and knocked off my train of thought so much that I couldn't even absorb the equation you posted 😱

 

[medicomel]

i'm like mr. peanut but truncated.

 

[kalix]

i'm like mr. peanut but truncated.

hahaha

 

[cfdavid]

Regarding titrations....i always messed up on the weak acid/strong base and weak base/strong acid....however, after thinking about it for a while, i came up with a good solution. As already stated Equivalence point of SA and SB equals 7. Titrate WA with SB...the SB will dissociate more than the weak acid, thus at the equivalence point, more base will be in solution than acid (thus more OH), then causing equivalence point to be greater than 7. Same thing applies to SA and WB, only opposite. At equivalence, more acid is dissociated, thus more H, thus decrease in PH, thus the equivalence point benig smaller than 7.

.

If I am incorrect here, forgive me, but I think that this is worth clarifying. As I understand it, at the equivalance point, the only remaining products in a Weak AorB/Strong AorB Titration is the salt and water.

Yes, it's true that a weak acid will dissociate more that a strong base, but when you mix the two together, regardless of any 'reluctancy' on the part of the weak acid, the strong base gives that proton no choice but to dissociate. It simply 'pulls' it right off. So, when equal numbers of a strong titrant has been added to a weak acid or base solution, at the equivalence point, the only products should be salt and water.

Thus, the impact on pH at the equivalence point is due to the strength of the conjugate acid or base that is the component of the salt. The water is pH 7, so if the conjugate acid (for example) is a weak base, it will influence the pH to be higher than the 7 that water alone 'contributes'. It does this by pulling some (only some as it is probably a weak base) protons from water, thereby increasing the concentration of OH- ions ever so slightly from the standard 10^-7. Thus, the pH will show greater than 7, at the equivalence point in this case.

Again, I'm pretty sure this is the correct way to view it. Perhaps QofQuimica or Shrike would like to elaborate if needed.

 

[Shredder]

The simple way to remember the pH at the equivalence point of a weak/strong combination is that it will lie in the direction of whichever one is stronger. I haven't found it necessary to analyze it further than that so far, and I think this is a correct way to look at it.

Can anyone review optics when objects are placed in front of foci? I see this occasionally, and it throws off the general rules about upright/inverted and real/virtual. Do you just flip them both when you move from beyond to in front of the focus? Can this phenomenon be observed in diverging and converging lenses and mirrors? I also find that buoyant force and related equations keep slipping from my mind even after studying it...gotta refresh once again soon.

 

[cfdavid]

Can anyone review optics when objects are placed in front of foci? I see this occasionally, and it throws off the general rules about upright/inverted and real/virtual. Do you just flip them both when you move from beyond to in front of the focus? Can this phenomenon be observed in diverging and converging lenses and mirrors? I also find that buoyant force and related equations keep slipping from my mind even after studying it...gotta refresh once again soon.

Yeah, for concave mirrors and convex lenses, if the object is a shorter distance from the lense or mirror than the focal point, the image will be negative, virtual, and upright. I just hope they don't pull that crap on the test.

With buoyant force, I find it helpful to keep in mind the difference between floating and being completely submerged. One factor that we've all kind of been programmed to think is that somehow air in our lungs is what would help keep us afloat while swimming. Or, that we were able to stay closer to the bottom of the pool 'due' to letting the air out of our lungs. When, in fact, it has nothing to do with air, but rather the increased volume of our bodies when we hold in air as our diagragms stay flexed, expanding our rib cage. Thus, we are able to displace more water (thus more mass of water). And this is what allows us to float better in such a situation. The opposite is true of letting the air out of our lungs, thereby decreasing the volume of our bodies etc.

Another analogy that may be useful to some (the MCAT likes these kinds of tie-ins) is the fact that you can hold your breath underwater for a longer period of time when you dive down deeper. What is happening is that as you go deeper (with a full breath of air in your lungs), the greater water pressure squeezes against your body and actually compresses the air in your lungs. This increases the total pressure of that volume of air. And with the total pressure increase, the partial pressure of oxygen increases. This increases the affinity of hemoglobin for oxygen in the lungs.

It's little factoids like these that help me to remember some of these physics topics.

*One thing to be aware of for the MCAT relative to electro-magnetism; Know that the equations F=qE, U=qED, and V=Ed ONLY relate to when you miraculously put a charge in a constant electric field.

The others are 'caused' by the point charge. F=kqq/r^2 E=kq/r^2 etc...

 

[BaylorGuy]

This thread hasnt had a lot of activity recently....i've decided it needs a bump as well as new info put into it.

Reading over some circulatory info...remember that Cardiac Output=Heart Rate*Stroke Volume (CO=HR*SV)....i don't know how important this may be, but i remember a question or two on this...they may have been discrete questions or something of the sort.

Remember Starling's Law....an increase in blood volume will lead to an increase in blood pressure.
Remember that osmotic pressure in capillaries stay constant while hydrostatic pressure decreases...overall, there is a net loss of fluid at the afferent end of the capillary and a net gain of fluid at the efferent end of the capillary.

And last but not least, immunology...T-Cells mature in the Thymus and are involved in the cell-mediated immunity, while B-Cells mature in the Bone marrow and are involved in humoral immunity (I.E. antibodies).

 

[cwb]

"Redox: Galvanic cell--OxidAtion occurs at Anode. anode is also negative pole. ReduCtion occurs at cathode. Ca+hode is positive pole. This reaction occurs spontaneously, thus emf is negative.
Electrolytic...same thing occurs, only anode is positive pole, cathode is negative pole. Rxn is non-spontaneous, emf is positive."

Just to clear up some possible confusion that might have come from a previous post...

A reaction in a Galvanic (Voltaic) Cell is spontaneous so the delta G is negative, However from the equation delta G = -nFEcell if the reaction is spontaneous Ecell (EMF of cell) must be positive. The EMF by the same relation for an electrolytic cell would be reversed on the same premesis (it would be negative). Not exactly sure if I am correct as I have not verified 100% that I am right but I'm pretty sure it's correct as I stated.

 

[cfdavid]

Remember the blood pressure spectrum.

From highest pressure to lowest:
Aorta, arteries, arterioles, dropping in the cappilaries, venules, hitting a low in the veins, and then increasing slightly in the pulmonary system (probably won't address this fact).

Also remember that although the capillaries represent a large total cross-sectional area, velocity is the slowest in the capillaires. Just think that it takes time for the gas exchange to be effective at an organ or muscle, so velocity must be lowered in the capillaries.

 

[TicAL]

You can remember the velocity relationship in capillaries by relating it to the concept of flow in Physics; Q = v x A. As flow remains constant, if the area increases (as it does in the capillaries) the velocity must decrease, which allows for effecient nutrient exchange along the alveoli.

In regards to respiration, know that it is controlled via the Medulla Oblongata. The Phrenic nerve innervates the diaphragm, which leads to contraction. Intercoastal muscles also contract to push the rib cage upwards. This contraction leads to an increase in volume in the lungs, which allows for air to flow in (inspiration) via a negative pressure differential. Relaxation of the diaphragm leads to a decrease in volume, which increases the pressure inside and forces air out (expiration).

Hemoglobin unloading of Oxygen occurs in increased temperatures, increased CO2 levels, and decreased pH.

 

[Shredder]

Concerning flow in pipes, fluids have slower velocity in pipes with greater diameter, and they have higher pressure. Faster moving fluids in narrow pipes have lower pressure. This is contrary to what you think when you imagine a high pressure jet of water. It has to do with Bernoulli's equation.

Pressure equals force/cross sectional area. A hydraulic pump is similar to a pulley system in that it lets you turn a small amount of force applied over a small area into a larger force over a larger area, thus giving equal pressures F/A. This is accounted for by work=Fd, meaning you have to push a small piston very far just to get a big piston to move a little.

Remember that work is measured in the parallel direction to the force, Fdcostheta. I missed this question on 4R. Anything to address in tension in cords and pulleys? That's a little convoluted and hard to explain without diagrams, I don't want to do it and I just hope nothing hard on it shows up.

 

[riceman04]

One more topic that I found I needed to dig a little deeper into is that of titrations. Again, I always like to put things into more simple terms.

First, I don't think that many of the review books do well to explain equivalence point very well. But the bottom line is that it's the point at which an equal number of moles of acid or base, is added to the unknown acid or base. That's how we can accomplish the goal behind the titration in the first place, which is to determine the concentration of the unknown solution (but it's easy to know what volume the unknown is since we just put it in a beaker).

So, if we have some unknown concentration of an organic acid that we found sitting in some jar in a lab (that may or may not dissociate completely), we would add a strong base such as KOH. The strong OH- simply pulls off all the Hydrogens regardless of acid strength.

Remember that Acid + Base = Salt and Water. Thus, if the salt is one of weak conjugates that don't impact pH, then essentially the only thing left in the solution to impact pH is water. Thus, in the case of HCl and KOH (strong acid and strong base), the salt is NaCl which doesn't impact pH. Therefore, the equivalence point will be at 7.

But, if you react NaOH with Acetic Acid (weak organic acid - as most organic acids are weak in relation to the stonger inorganic acids of HCl and HNO3), you will still get the 'salt' and water as products, but the conjugate base of acetic acid (acetate) DOES impact pH a bit as it's a weak base. So, the products are then Na+/Acetate- (the salt) and ofcourse Water. But, the acetate anion, being slightly basic will impact pH a bit, making the equivalence point (where all the acid and base forms the salt and water) slightly basic. So, on a titration curve of a weak acid with a strong base, look for the pH at the equivalence point to be greater than 7.

The same goes for titrating a weak base with a strong acid. The pH at equivalence point will be less than 7 (slightly acidic). I think this could garnish a few points on the MCAT.

I hope this helps a bit for anyone that's been away from gen. chem for awhile, or like I said, just never had this stuff explained very well.

you mean salt + water + heat right?

 

[riceman04]

Concerning flow in pipes, fluids have slower velocity in pipes with greater diameter, and they have higher pressure. Faster moving fluids in narrow pipes have lower pressure. This is contrary to what you think when you imagine a high pressure jet of water. It has to do with Bernoulli's equation.

Pressure equals force/cross sectional area. A hydraulic pump is similar to a pulley system in that it lets you turn a small amount of force applied over a small area into a larger force over a larger area, thus giving equal pressures F/A. This is accounted for by work=Fd, meaning you have to push a small piston very far just to get a big piston to move a little.

Remember that work is measured in the parallel direction to the force, Fdcostheta. I missed this question on 4R. Anything to address in tension in cords and pulleys? That's a little convoluted and hard to explain without diagrams, I don't want to do it and I just hope nothing hard on it shows up.

For tension in pulley's cant you just combine the masses, depending on what they ask you?

 

[cfdavid]

With respect to replication; Remember that DNA Polymerase READS 3' to 5', but replicates 5' to 3'. Note the importance of Primase (an RNA primer) on the lagging strand of the replication fork.

Also, for translation, make sure to remember AUG as a start codon (and you may wish to remember that AUG calls for methionine). The stop codons are UAG, UAA, UGA.

Recall that when the Anti-codon on t-RNA is written out, it is written out in the conventional 5' to 3' direction. But, to actually determine the Anti-codon sequence of nucleotides, read the mRNA template 5' to 3' from left to right. Then just take the complement to that considering that the t-RNA will be coming in 3' to 5' if reading left to right. However, you must write the t-RNA anti-codon 5' to 3'.

The common example is the mRNA start codon of 5' AUG 3'. So, the anti-codon would be, reading left to right, 3' UAC 5'. But, the answer would be written conventionally as 5' CAU 3'.

Also, make sure you realize that the genetic code is relative to the mRNA template. So, if you are given a table of what sequences code for what amino acids, remember that the nucleotide sequences are the mRNA sequences (not t-RNA), that determine which amino acid the t-RNA brings to the ribosome.

Kind of a lot to keep straight, and you need to be carefull on these problems. So, it's worth spending some time on.

 

[mkitty]

Does anyone remember what 2,3-DPG does to the oxygen saturation curve? I want to say it shifts the curve to the left, so, like fetal blood, hemoglobin has a higher affinity for O2. Or does it shift to the right where more O2 unloading occurs? This detail's buried in my notes somewhere...

 

[laya533]

Does anyone remember what 2,3-DPG does to the oxygen saturation curve? I want to say it shifts the curve to the left, so, like fetal blood, hemoglobin has a higher affinity for O2. Or does it shift to the right where more O2 unloading occurs? This detail's buried in my notes somewhere...

It shifts it to the right(like increase in CO2,H+, and temperature)
the fetal hemoglubin is to the left

 

[BaylorGuy]

For those of you in biochem or have taken biochem, you should relate how 2,3-DPG (or 2,3-BPG) affects the binding of hemoglobin. The 2,3-DPG stabilizes the terse form of hemoglobin, leading to its unloading of O2 because the compound binds to the hole in the middle of the 4 alpha chain quaternary structure. Because of this, the hemoglobin will not bind O2, thus it will move the curve to the right.

For those who do not understand the above...do not worry, I'm fairly certain (99.9%) that this will not be touched on the MCAT.

 

[cfdavid]

How about a little Doppler Effect.

Qualitatively, when a large semi-truck is speeding towards you, the sound increases in pitch. This is because the frequency is increasing, while the wavelength gets shorter. Then, as it passes you, the opposite happens. The frequency is less, while the wavelength increases.

The equation is delta-freq./freq. source = relative velocity/wave velocity.

The relative velocity is best approached qualitatively as well. If you are standing still while the truck is racing towards you, and the truck is moving at 15 m/s, the relative velocity is 15 m/s. But if you're moving toward it at 5 m/s, the relative velocity (v) is 20m/s, and so on.

The denominator, wave velocity, is simply the velocity of a wave in a given medium. Most likely this will be air.

The change in frequency is the frequency of the observed minus the source frequency. You can internalize the source frequency as being the frequency of the trucks engine (which would be constant if traveling at a constant velocity- just steadily humming along). So, the truck is constantly eminating this 'noise', or frequency.

That being said, I've seen more problems ask for a qualitative answer to a Doppler Effect problem. But, the equation is good to know.

 

[jon0013]

can someone give the big picture of capillaries....

i know at arteriole end: hydrostatic force is greater than osmotic pressure so net fluid flows out

at venule end Osmotic P>>>hydrostatic pressure so net fluid flows in

blood flows from arteriole to venule...

i just dont know how this all fits together...thanks

 

[samnite]

4 equations & 4 Right-hand rules rules:

1) F=qvBsin@
Magnetic force for positively charged moving particle:
Fingers along "v", curl them into "B", thumb gives you force direction

2) F=LIBsin@
Magnetic force for a moving rod:
Fingers along "I", curl them into "B", thumb gives you force direction

3) B=uI/2(pi)r
Magnetic field around wire

Point thumb in direction of "I", fingers wrap around wire like the "B" field.

4) B=uI/2r
Magnetic field at center of wire loop
Follow "I" with fingers, thumb gives you "B" field direction


🙂

 

[HistoRocks]

can someone give the big picture of capillaries....

i know at arteriole end: hydrostatic force is greater than osmotic pressure so net fluid flows out

at venule end Osmotic P>>>hydrostatic pressure so net fluid flows in

blood flows from arteriole to venule...

i just dont know how this all fits together...thanks

I think this is it. Blood flows from arteries to arterioles to capillaries to venules to veins. The pressure of course is greater the closer u are to the heart. This is reflected in the diameters of the various types of blood vessels. A vein is obviously much thinner than an artery. Capillaries are thin for diffusion purposes... oxygen goes out, CO2 goes in. The proportions of the three layers of tissue that make up a blood vessel - adventitia, media, intima - also differ from blood vessel to blood vessel. For example, an artery would contain much more tunica media (elastic connective tissue layer) than a vein, because its subject to a lot more stretching. Elastic connective tissue allows for recoil (try pinching ur skin).

 

[BaylorGuy]

In capillaries, there are two ends, the arteriole end and venule end. There are 2 main pressures that are acting on the particles/water in the capillaries that will influence diffusion....these 2 pressures being hydrostatic pressure and osmotic pressure.

Now, hydrostatic pressure is based on the pressure of the heart...as the fluid in a capillaries moves from arteriole to venule the pressure will be highest at the arteriole end and lowest at the venule end. Keep this in mind

Now, osmotic pressure is based on the hypertonic properties of the blood (more specifically due to the proteins that remain in the blood and cannot pass through the capillaries...if they do, something is wrong with the body). osmotic pressure creates a hypertonic solution to the institial space and will tend to move water into the capillary...this pressure is constant at both arteriole end and venule end. Why? protein stays in capillary, thus water will follow.

Now, the synthesis...at the arteriole end, there is a net flow of fluid out of the capillary into the interstitial space...the reason is because at the arteriole end, hydrostatic is greater than osmotic, thus the pressure forces water/fluids into the interstitial. At the venule end, there is a net flow of water/fluids into the capillary because osmotic is greater than hydrostatic.

 

[marimiyaz]

Great thread! And some great explanations of things too.

fungi - they're haploid usually and their cell walls are made of chitin. They can reproduce sexually or asexually, it's difficult to treat fungal infections (they're not responsive to antibiotics).

4 most common bacterial shapes:

cocci-spherical
bacilli-rod
vibrio-comma shaped
spiral-spiral shaped

viruses are obligate intracellular parasites and can't make their own ATP. they can go through either lytic or lysogenic phases (dormant).

DNA transcribed from retroviral genome is called a provirus and depends on reverse transcriptase which humans don't have. it's used in genetic recombination techniques.

Does anyone have a good grasp of the different lab/genetic techniques? The ones i always forget are:

extraction (i know its general purpose but i forget the subtleties like adding weak base to extract acid? by the way i'm not sure if that's correct in fact it's probably wrong).

PCR

Southern/Northern Blotting

Western Blotting

 

[riceman04]

With respect to replication; Remember that DNA Polymerase READS 3' to 5', but replicates 5' to 3'. Note the importance of Primase (an RNA primer) on the lagging strand of the replication fork.

Also, for translation, make sure to remember AUG as a start codon (and you may wish to remember that AUG calls for methionine). The stop codons are UAG, UAA, UGA.

Recall that when the Anti-codon on t-RNA is written out, it is written out in the conventional 5' to 3' direction. But, to actually determine the Anti-codon sequence of nucleotides, read the mRNA template 5' to 3' from left to right. Then just take the complement to that considering that the t-RNA will be coming in 3' to 5' if reading left to right. However, you must write the t-RNA anti-codon 5' to 3'.

The common example is the mRNA start codon of 5' AUG 3'. So, the anti-codon would be, reading left to right, 3' UAC 5'. But, the answer would be written conventionally as 5' CAU 3'.

Also, make sure you realize that the genetic code is relative to the mRNA template. So, if you are given a table of what sequences code for what amino acids, remember that the nucleotide sequences are the mRNA sequences (not t-RNA), that determine which amino acid the t-RNA brings to the ribosome.

Kind of a lot to keep straight, and you need to be carefull on these problems. So, it's worth spending some time on.

Also to add to that:
remember that you can use an formula to find the total number of ATP needed to complete the process of translation for a specific polypeptide:
the formula is: 4ATP/AA - 1ATP

 

[riceman04]

In capillaries, there are two ends, the arteriole end and venule end. There are 2 main pressures that are acting on the particles/water in the capillaries that will influence diffusion....these 2 pressures being hydrostatic pressure and osmotic pressure.

Now, hydrostatic pressure is based on the pressure of the heart...as the fluid in a capillaries moves from arteriole to venule the pressure will be highest at the arteriole end and lowest at the venule end. Keep this in mind

Now, osmotic pressure is based on the hypertonic properties of the blood (more specifically due to the proteins that remain in the blood and cannot pass through the capillaries...if they do, something is wrong with the body). osmotic pressure creates a hypertonic solution to the institial space and will tend to move water into the capillary...this pressure is constant at both arteriole end and venule end. Why? protein stays in capillary, thus water will follow.

Now, the synthesis...at the arteriole end, there is a net flow of fluid out of the capillary into the interstitial space...the reason is because at the arteriole end, hydrostatic is greater than osmotic, thus the pressure forces water/fluids into the interstitial. At the venule end, there is a net flow of water/fluids into the capillary because osmotic is greater than hydrostatic.

And that is one of the reasons why we have a lymph system (sorry I made a bad typo before) -- to shuttle this fluid back into the circulatory system (somewhere up closer to your heart. I cannot remember off hand right now though)

 

[riceman04]

For those of you in biochem or have taken biochem, you should relate how 2,3-DPG (or 2,3-BPG) affects the binding of hemoglobin. The 2,3-DPG stabilizes the terse form of hemoglobin, leading to its unloading of O2 because the compound binds to the hole in the middle of the 4 alpha chain quaternary structure. Because of this, the hemoglobin will not bind O2, thus it will move the curve to the right.

For those who do not understand the above...do not worry, I'm fairly certain (99.9%) that this will not be touched on the MCAT.

Ok, so I will add to this (but basically say the same things):

2,3-Bisphosphoglycerate (2,3-BPG) is produced in the red blood cells from the metabolism of glucose. So as was stated above, BPG lowers affinity of Hb for 02.
Before I go on I will review a bit: Hb has a relaxed (R-state, known as Oxy-Hb) state, meaning that is has 02 bound (i.e higher affinity), and a tense (T-state, known as Deoxy-Hb) state.
Also recall that it consists of 4 subunits (alpha1beta1, alpha2beta2) that are, when in the T-state, stabilized by salt bridges between chains. When O2 binds to the site is causes one of the pairs of dimer peptides mentioned above to rotate, and open up a 15 degree cleft btwn the two pairs. This action is what helps incr affinity.
Now back to the affects of 2,3-BPG (when Hb is down in the tissues): The binding site for BPG is in the 15 degree cleft created (see above). In the lungs, when 02 is bound, the cleft becomes too small for BPG binding, thus increased affinity for O2 in the lungs.

Keep in mind that BPG will bind down in the tissues where affinity for Hb is already low.

I can also tell you the specific effects of H+ and CO2, but only if people want me to do so.

cya!

 

[cfdavid]

4 equations & 4 Right-hand rules rules:

1) F=qvBsin@
Magnetic force for positively charged moving particle:
Fingers along "v", curl them into "B", thumb gives you force direction

2) F=LIBsin@
Magnetic force for a moving rod:
Fingers along "I", curl them into "B", thumb gives you force direction

3) B=uI/2(pi)r
Magnetic field around wire

Point thumb in direction of "I", fingers wrap around wire like the "B" field.

4) B=uI/2r
Magnetic field at center of wire loop
Follow "I" with fingers, thumb gives you "B" field direction


🙂

Magnetic fields always point from North to South, just like Electric fields.

**When answering questions, make sure you read carefully for "current" versus electrons. I've missed a few because I was thinking electrons, but the question stated current. Ofcourse, they flow in opposite directions.

Also, the force acting on a charged particle as it moves with some velocity through a B field can be set equal to the centripetal force mv^2/r

qvB=mv^2/r And you can algebraically solve for the radius of curvature that the charged particle will follow due to the force acting on it.

 

[cfdavid]

For PCR (polymerase chain reaction), the key benefit is that you do not have to add a new batch of expensive DNA Polymerase.
There's a good reason for this; The replication 'machinery' used in the super replication process is from bacteria cells that where found in a very hot environment. So, the replication machinery 'lives' through the hot process needed to continually denature all the DNA after each cloning step.

1)Take DNA that you wish to clone the heck out of.
2)Heat it up to break the H-bonds between the 2 strands.
3)DNA primers then get attracted to the separated strands through base pairing.
4) The special, heat resistant, DNA Pol then replicates the batch of primed DNA strands.

*The process can be repeated many times without adding new DNA Pol. So, it's fast and economical.

I'm open to more info on Blotting, but I've sorted through to get to the bottom line:

The goal is to identify certain segments of DNA, RNA, or protein (depending on which blotting technique used). The 'certain segments' are targets that you already know, but want to see if the samples contain those target sequences. In other words, you know what you are looking for, but you don't know if you have it or not.

So, you have a bunch of this unknown DNA. You want to see if it contains your little DNA fragment (a sequence that makes an important protein that is critical to your research).

First, cleave your long DNA strands into into segments of varying size using restriction enzymes.
Now, use gel electrophoresis to separate out different sized fragments so the the same sized fragments will congregate in the gel.

Now, denature the DNA fragments into separate strands so that you can add a radioactive DNA strand that codes for your special target protein that you are interested in.

If the 'batch' of unknown DNA has that special sequence of interest, the radioactive DNA strand will 'mate'/hybridize with one of the strands in the separated batches of 'like' strands.

Thus, you now have isolated the sequence of interest.

 

[TicAL]

The goal of Southern Blotting (immunoblotting) is to use antibodies to detect the presence of proteins. First the sample containing the protein is run on a polyacrylamide gel (similar to the way DNA is run on agarose). The proteins are then transfered to a nitrocellulose filter by placing the filter on the gel and adding current. After it is transferred, "primary" antibodies that bind to the protein you are looking for are added to the filter. "Secondary" antibodies are then added on top of that; these secondary antibodies bind to the primary antibodies which are attached to the protein, and contain a protein complex that allows them to luminesce. Finally, peroxidase is added to detect the fluorescence and the sample can be analyzed via x-ray sheets. I highly doubt you'd need to know any of this for the MCAT 😉

Can someone offer a definitive word as to how much net ATP is produced in cellular respiration. I'm getting various numbers from different sources (38, 36, 30). If you could include the sources of the ATP production (NAD, FAD, GTP) that'd be golden 🙂

 

[SilvrGrey330]

Can someone offer a definitive word as to how much net ATP is produced in cellular respiration. I'm getting various numbers from different sources (38, 36, 30). If you could include the sources of the ATP production (NAD, FAD, GTP) that'd be golden 🙂[/QUOTE]


Hmm. this is from memory, lets see, this is for 1 molecule of glucose:

1) Glycolysis --> Occurs in the cytosol on the cell

Makes 4 ATP, but uses 2 of it, so nets 2 ATP, and makes 2 Pyruvates and 2 NADH, so in summary:

2 ATP
2 Pyruvates
2 NADH

2) Pyruvate Decarboxylation --> Mit Matrix

Object is to regenerate NAD+
it makes 2 NADH

3) Kreb Cycle --> Mit Matrix

2 GTP
6 NADH
2 FADH2

4) ETC --> Inner mitrochrondial membrane

This is where the math begins, You take everything from above, and add up you ATP's, GTP = ATP, and 1 NADH = 3 ATP, 1 FADH2 = 2 ATP

2 ATP + 2 GTP = 4 ATP
10 NADH * 3 = 30 ATP
2 FADH2 * 2 = 4 ATP
-----------------------
Prokaryotes = 38 ATP
Eukaryoties = 36 ATP --> We had to pay a $ 2ATP toll to get into the ETC,
whereas prokaryotes dont need to, b/c their
respiration is already all happenin the plasma memb



NB: these are the numbers mcat wants us to know, today, biochemists actually believe that NADH contributes to 2.5 atp on average and FADH contributes about 1.5 atp, but this could create fractions and gets too messy for the test's purpose.

 

[tsazmand]

Overview of Cellular Respiration
give credit to-->http://www.mansfield.ohio-state.edu/~sabedon/biol1100.htm


# ATP
step

-2
priming glycolysis

+4
substrate level phosphorylation (glycolysis)

+6
2 NADH produced (glycolysis)

-2
transportation of two NADH into mitochondria

+6
2 NADH produced in conversion of pyruvate to acetyl-CoA

+18
6 NADH produced during Kreb's cycle

+4
2 2"FADH2 produced during Kreb's cycle

+2
substrate level phosphorylation (Kreb's cycle)

+36
total ATPs produced from one glucose from aerobic respiration in eucaryotes. Compare with total from glycolysis alone (i.e., 2 ATP).

sometimes 38 ATP, for example, in certain procaryotic systems.

 

[tsazmand]

also the reason only 2 ATP r made per NADH in Glycolysis is because the e- are shuttled into the middle of the ETC chain, therefore skipping cytochrome complex or smth like that, therefore producing 2atp instead of 3 per NAD+

 

[riceman04]

Can someone offer a definitive word as to how much net ATP is produced in cellular respiration. I'm getting various numbers from different sources (38, 36, 30). If you could include the sources of the ATP production (NAD, FAD, GTP) that'd be golden 🙂

Hmm. this is from memory, lets see, this is for 1 molecule of glucose:

1) Glycolysis --> Occurs in the cytosol on the cell

Makes 4 ATP, but uses 2 of it, so nets 2 ATP, and makes 2 Pyruvates and 2 NADH, so in summary:

2 ATP
2 Pyruvates
2 NADH

2) Pyruvate Decarboxylation --> Mit Matrix

Object is to regenerate NAD+
it makes 2 NADH

3) Kreb Cycle --> Mit Matrix

2 GTP
6 NADH
2 FADH2

4) ETC --> Inner mitrochrondial membrane

This is where the math begins, You take everything from above, and add up you ATP's, GTP = ATP, and 1 NADH = 3 ATP, 1 FADH2 = 2 ATP

2 ATP + 2 GTP = 4 ATP
10 NADH * 3 = 30 ATP
2 FADH2 * 2 = 4 ATP
-----------------------
Prokaryotes = 38 ATP
Eukaryoties = 36 ATP --> We had to pay a $ 2ATP toll to get into the ETC,
whereas prokaryotes dont need to, b/c their
respiration is already all happenin the plasma memb



NB: these are the numbers mcat wants us to know, today, biochemists actually believe that NADH contributes to 2.5 atp on average and FADH contributes about 1.5 atp, but this could create fractions and gets too messy for the test's purpose.[/QUOTE]

I thought it is:
Prokaryotes: 32ATP
Eukaryotes: 30 ATP

 

[UCdannyLA]

i'm taking the april mcat.

I stopped reviewing, even though I didn't memorize everything hardcore, and I just keep taking practice full lengths...I've taken five in the past 8 days (3R-8)...even though i'm not reviewing that much between the full lengths (just going over the errors mainly) my score is getting better.

1st full length (8 days ago): 9PS, 9VR, 9PS
2nd: 10, 9, 11
3rd: 10,10,10
4th: 11,10,11
5th, today: 12, 11, 12

Today was really good, I don't know, maybe it was a fluke...I'll take another full length on saturday. I just feel more confident now...and I kinda got a "feel" for the MCAT, if that makes any sense. I think that is what allowed me to break the plateau score of 10,10,10 that I was hovering around. I realized that you don't need to memorize all that friggin science, you just have to understand the important concepts and know a couple of important formulas. It just clicks now for some reason, I used to have trouble finishing PS and BS, but now I finish with 5-15 minutes left. So I guess my point is...don't stress out about memorizing every little detail...just understand and apply...a lot of the MCAT questions can be answered correctly based on your intuition alone. Well that's my theory.

Verbal...that's another story. I can't seem to break 10-11 plateau no matter how hard i try. I'm just too slow of a reader.

 

[BaylorGuy]

Verbal is the biggest problem i have. I'm averaging 12s in BS and PS, but the verbal is just all over the place, sometimes 11, 10, today was an 8 (Took AAMC 7 today and got a 32...PS=12 VR=8 BS=12). Lets just hope that there are easier verbal passages on the real thing in april.

UCDanny, you really hit the mark. Its not a big memorization game...its about how to apply all the stuff that you know into some kind of super-unified theme thingy. I dont know what i'm talking about anymore. This last week is gonna be super stressful because i've got one more full length left before the big dance and i'm gonna try and review all the basics before i pretty much quit on thursday and work on my sleep schedule.

One last note/question...i realized that i havent really been practicing my writing sample at all. I can answer the three tasks but i can't really write the unified essay part. Anyone have any pointers or advice for this???

 

[firebird69guy]

And that is one of the reasons why we have a lymph system (sorry I made a bad typo before) -- to shuttle this fluid back into the circulatory system (somewhere up closer to your heart. I cannot remember off hand right now though)

thoracic duct empties back into circulation

 

[aye]

i'm taking the april mcat.

I stopped reviewing, even though I didn't memorize everything hardcore, and I just keep taking practice full lengths...I've taken five in the past 8 days (3R-8)...even though i'm not reviewing that much between the full lengths (just going over the errors mainly) my score is getting better.

1st full length (8 days ago): 9PS, 9VR, 9PS
2nd: 10, 9, 11
3rd: 10,10,10
4th: 11,10,11
5th, today: 12, 11, 12

Today was really good, I don't know, maybe it was a fluke...I'll take another full length on saturday. I just feel more confident now...and I kinda got a "feel" for the MCAT, if that makes any sense. I think that is what allowed me to break the plateau score of 10,10,10 that I was hovering around. I realized that you don't need to memorize all that friggin science, you just have to understand the important concepts and know a couple of important formulas. It just clicks now for some reason, I used to have trouble finishing PS and BS, but now I finish with 5-15 minutes left. So I guess my point is...don't stress out about memorizing every little detail...just understand and apply...a lot of the MCAT questions can be answered correctly based on your intuition alone. Well that's my theory.

Verbal...that's another story. I can't seem to break 10-11 plateau no matter how hard i try. I'm just too slow of a reader.

i think i know what you're talking about in terms of the "feel".... but i'm still getting alot wrong do you think that "fell" of the mcat will be altered if you take kaplan/tpr full lengths since you'd get used to their style??

 

[danesh23]

bump

 

[BaylorGuy]

Found some more info that may be helpful..

Isomers:
Most Different----------------------------------------------------------------------Most Similar
Structural.....................Diastereomers (including geometric)........Enantiomers........Conformation

Structural=Has the same molecular formula
Geometric=cis or trans (Z or E)
Diastereomers=stereoisomers that are not mirror images
Enantiomers=non-superimposable mirror images
Conformation=differ in rotation around a bound

-For cyclohexane these are the most stable conformations when in the chair formation...trans-1,2...cis-1,3...trans-1,4
always remember that the most stable position is equatorial

-SN1 rxns lose chirality...SN2 rxns invert chirality

 

[richardlo]

In EK physics, there's a picture of a guy standing on land while looking at the image of a fish in the water. It shows how the light rays (eminating from the fish) bend away from the normal as they enter the air. So, the guy thinks he's looking at the fish, but in reality, due to how light bends when traveling through different media, he's looking at the image of the fish, which is behind the real thing.

It reminds me of when I was a kid and used to try shooting the fish in my grandpa's lake with my bee-bee gun. I would always miss, even when I was sure I had it 'locked' in.

Well, if I had known simple optics when I was 10, I would have aimed in front of the damn thing.

Did you (or anyone else) finish every single question on those 1001 books? Thanks. I ask because the image of fish question appears to be at the very end of the 1001 physics book...