Biochemistry, cell biology, and genetics question thread

[Nutmeg]

All users may post questions about MCAT, DAT, OAT, or PCAT cell/molecular biology, genetics, and biochemistry here. Anatomy, physiology, development, embryology, and evolution questions should be posted in the other biology thread. We will answer the questions as soon as we reasonably can. If you would like to know what biology topics appear on the MCAT, you should check the MCAT Student Manual (http://www.aamc.org/students/mcat/s...anual/start.htm)

Acceptable topics:
-general, MCAT-level biology.
-particular MCAT-level biology problems, whether your own or from study material
-what you need to know about biology for the MCAT
-how best to approach to MCAT biology passages
-how best to study MCAT biology
-how best to tackle the MCAT biological sciences section

Unacceptable topics:
-actual MCAT questions or passages, or close paraphrasings thereof
-anything you know to be beyond the scope of the MCAT

*********

If you really know your cell/molecular biology, I can use your help. If you are willing to help answer questions on this thread, please let me know. Here are the current members of the Cell/Molecular Biology Team:

-Nutmeg (thread moderator): My background is in neurobiology. Please note that I am nocturnal, and generally only post between the hours of 10pm and 8am PST.

I'm going to make this thread a bit different than the others, because the material covered in the BS section is a bit different. With o-chem, gen-chem, and physics, there are a number of core concepts to understand. While there is also a lot of that in the BS, there is also a great deal of specific knowledge involved in this section (relative to the others). Test questions often introduce an experimental set-up, asking for either expected results or the interpretation of results. As such, passages might relate to advanced concepts that you are not expected to know coming into the test, and that they will explain in the passages. Any familiarity that you have with these concepts will make the test easier.

While in general this forum is designed for people studying for the MCAT, I welcome any questions relating to molecular biology, even though they might be beyond the scope of the MCAT. I know some people also like to use these threads to get help on homework questions, and I welcome that, too.

-LT2: LT2 is finishing her MS in microbiology.

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[tennisboy85]

Thanks for the post. I guess I learned something new today!

 

[axp107]

AHHH! the word "plasma" is confusing me here

An increased plasma osmolarity would result in:

A) decreased permeability to water in nephron
B) increased ADH secretion

Before looking at the answer, I assumed the word "plasma" was referring to the filtrate.. if it were talking about the blood, wouldn't it just say blood osmolarity?

Ok so assuming it was the filtrate, I picked A) since osmolarity levels would have to return back to normal in the filtrate

B) is the answer.. b/c ADH increases water reabsorption.. decreasing plasma osmolarity. The only thing I could conclude is that the "plasma" referred to blood circulating the body, not the filtrate

 

[corbis11]

I believe they are only going to say plasma when referring to the actual plasma that is a constituent of blood. The plasma is the part of the blood that contains proteins which contributes to the colloidal osmotic pressure. So an increase in the plasma osmolarity would result in ADH release so that water will be reabsorbed so that plasma osmolarity is lowered

 

[RoadRunner17]

In excretory systems, plasma I think refers mainly to the fluid in the interstitial cells immediately surrounding the nephron. When plasma osmolarity is high, it means water will want to move across the nephron into the interstitial cells, usually because of a solute gradient. In the end we're talking about plasma vs filtrate.

 

[axp107]

Does mitochondria replicate through binary fission?

Doesn't really seem to make sense.. however, I can see a roman numeral question on this.

I know its DNA replicates separately...

 

[corbis11]

Yes. just remember that mitochondria are like "dumbed-down" bacteria that have their own circular DNA and they have many copies of it.

 

[axp107]

1) What is the function of a coenzyme? cofactor?

2) what's the difference between a coenzyme and cofactor

3) I remember reading somewhere that NAD or NADH was a cofactor or something.. is it?

Thanks!

 

[tik-tik-clock]

But I cant figure out what this statement really means

The WBC cell membrane has a membrane protein that
is in proximity to the THC receptor and interferes with
THC binding.

Thanks!

 

[eltor07]

1) What is the function of a coenzyme? cofactor?

2) what's the difference between a coenzyme and cofactor

3) I remember reading somewhere that NAD or NADH was a cofactor or something.. is it?

Thanks!

1) Function is to bind to an enzyme and stabilize the active conformation of an enzyme. Enzymes are always oscillating between their inactive and active states so when the cofactor/coenzyme binds to it, it makes it easier for the substrate to complex with the enzyme.

2) Coenzymes are cofactors. Only difference is coenzyme are organic molecules, while cofactors are metal ions (inorganic).

3) Yes, NADH is a cofactor because it aids enzymes by giving them electrons.

 

[axp107]

Thanks a lot for the reply!

I'm trying to compare bacteria with mitochondria...

1) In bacteria, where does the Kreb's cycle take place?

2) What about the whole "electron-transport chain"? Is there some structure in the bacteria that corresponds to the intermembrane space? Thanks

 

[eltor07]

1) I believe the Kreb's cycle would take place in the cytosol.

2) Electron transport, I believe is on the plasma membrane.

 

[axp107]

Why is a decrease in pH associated with increased CO2 levels.. doesn't CO2 turn into bicarbonate ions?.. and bicarbonate ions are basic

 

[gymgirl]

Why is a decrease in pH associated with increased CO2 levels.. doesn't CO2 turn into bicarbonate ions?.. and bicarbonate ions are basic

Removing CO​

2 would shift the equilibrium shown below towards the left, decreasing the H+ concentration in the blood and thus, increasing the pH. The body uses this technique (hyperventilation)
as a means of regulating plasma pH.
CO2 + H2<-> H2CO3 <-> H+ HCO3​

 

[axp107]

What actually recognizes the pathogen in the first place?

Theres the.. general response.. histamine release, inflammation etc... macrophage activation

then the specific responses (humoral/cell-mediated immunity)

What I don't understand is... what types of cells actually recognize the pathogen in the first place... is it the macrophages?

 

[Summer Sweet]

2) What about the whole "electron-transport chain"? Is there some structure in the bacteria that corresponds to the intermembrane space? Thanks

I vaguely remember the bacteria version, but I'm not sure if it's within the scope of the MCAT. The chain should be on the plasma membrane, and I think the proton gradient is slightly different so the pump functions differently. I didn't study this in depth, but I saw a passage on a PR practice test where they explained everything anyway.

 

[Genie133]

When are we able to assume that something is sex linked? For example, just because only males have a certain structure (for example #131 in CBT 8, in the BS section) does not mean that the structure is sex linked. Why not?

What is a good way for determining whether something is sex linked dominant or sex linked recessive? or autosomal?

 

[corbis11]

look at post #287

 

[Summer Sweet]

When are we able to assume that something is sex linked? For example, just because only males have a certain structure (for example #131 in CBT 8, in the BS section) does not mean that the structure is sex linked. Why not?

What is a good way for determining whether something is sex linked dominant or sex linked recessive? or autosomal?

If it is dominant, it should more or less appear in every generation.
If it is recessive, it might skip a generation.
If it is sex-linked, then more males have it than females. If the father has it, the son will have it but the daughter might not. And a son might have it if the mother is a carrier but does not have it.
If it Y-linked, then obviously no females will have it.

 

[Summer Sweet]

Are there free ribosomes in the nucleus? I've been thinking about this one for a while, and I still can't be sure. Ribosomes are used in translation, which occurs in the cytoplasm. But would they serve any function in the nucleus--do they aid in maybe transcription?

What is the 9+2 arrangement for microtubules?

Genetics ques:
You have 2 copies of each gene--from mom and dad. So one is supposed to be spontaneously inactivated, right? Something like being a barr body? Or is that only for the X chromosome in females? Anyway, if one chromosome is inactivated randomly from every pair, how could you only express the dominant trait (in terms of the whole dominant/recessive thing)? If the copy that is inactivated is random, and if the dominant one was inactivated, would you ever be able to accept the recessive trait? I was reading up on genetics last night and this stuff got more confusing as I thought about it more.

 

[EmiliaC]

Genetics ques:
You have 2 copies of each gene--from mom and dad. So one is supposed to be spontaneously inactivated, right? Something like being a barr body? Or is that only for the X chromosome in females? Anyway, if one chromosome is inactivated randomly from every pair, how could you only express the dominant trait (in terms of the whole dominant/recessive thing)? If the copy that is inactivated is random, and if the dominant one was inactivated, would you ever be able to accept the recessive trait? I was reading up on genetics last night and this stuff got more confusing as I thought about it more.

I think this is beyond the scope of what would ever appear on the MCAT, but from my understanding, no, not really. X inactivation occurs in human and various other mammalian females because you only need 1x of the genes on the X chromosome for proper functioning - in other organisms, they might have evolved to need 2x, so instead of silencing in females, males hypertranscribe their X.

For all non-sex chromosomes, I assume that we get both copies and both are transcribed when need be. The dominant trumpts the recessive, but there are also cases of codominance/incomplete dominance/polygenetic traits. Consider skin color, especially when one parent is dark and the other is light - the kid is usually a mix of the two because neither sets of genes for skin color are completely dominant over the other. If silencing occured, the kid would be one or the other, but not an intermediate.

 

[axp107]

For muscle contraction, calcium release is needed from the sacroplasmic reticulum...

you know how calcium is also released in between nerve synapses... for a neurotransmitter to cause depolarization... is that separate from the sacroplasmic reticulum calcium release?

 

[Krazykritter]

Sarcoplasmic reticulum is a specialized type of ER (smooth-type) that is specific to smooth & striated muscle. It basically stores calcium so that there can be a quick release of Ca++ once the Ryanodine receptor is stimulated.

I don't know if you necessarily need to know the name of the Ryanodine receptor for the MCAT...maybe someone else can help w/ that?

Also, Ca++ release doesn't usually happen at the nerve synapse b/c Ca++ isn't an NT. Ca release occurs near the nerve terminal where it controls the amount of NT that will migrate to the synaptic terminal in synaptic vesicles. Again, I don't know if that is something that the MCAT will test on since it's been so long since I've taken it.

 

[HristosKaran]

In an anemic individual, compensation to maintain adequate oxygen delivery to the tissues involves increasing the hemoglobin concentration in RBCs. For each molecule of hemoglobin added to the RBC, how many atoms of iron are added, and how much more oxygen can be held, respectively?
1 and 1
1 and 4
4 and 1
4 and 4

[Show/hide explanation]

D

Recall that hemoglobin is composed of 4 subunits that each contain a core iron atom, and that each of these four subunits is able to bind one molecule of oxygen. Choice (D) is the correct answer.


Now, I put A, 1 to 1, b/c it asks for the number of iron and oxygen molecules per RBC does it not? Or am I going crazy?

 

[Krazykritter]

Each hemoglobin molecule (in the adult) is composed of 2 alpha & 2 beta subunits. Each of these subunits has a Fe atom in their center. So the answer to the first part is that 4Fe atoms are added.

Each subunit can additionally bind to one molecule of oxygen under the proper circumstances (Bohr effect) so 4 oxygen can be held.

Answer is correct @ 4:4.

Hemoglobin picture: http://fig.cox.miami.edu/~cmallery/150/chemistry/hemoglobin.jpg

 

[HristosKaran]

Each hemoglobin molecule (in the adult) is composed of 2 alpha & 2 beta subunits. Each of these subunits has a Fe atom in their center. So the answer to the first part is that 4Fe atoms are added.

Each subunit can additionally bind to one molecule of oxygen under the proper circumstances (Bohr effect) so 4 oxygen can be held.

Answer is correct @ 4:4.

Hemoglobin picture: http://fig.cox.miami.edu/~cmallery/150/chemistry/hemoglobin.jpg

Ohhh....I knew about the alpha-beta subunits, but I thought they all complexed ONE iron molecule....Thanks for the help!!

 

[axp107]

Anyone know what rapid cycling is? In terms of the cell cycle?

 

[QofQuimica]

bump

 

[QofQuimica]

bump

 

[QofQuimica]

bumpity

 

[NickMB]

Anyone know what rapid cycling is? In terms of the cell cycle?

Rapid cell cycling occurs in early embryonic development. Inhibition of rapid cell cycles in early-stage embryos results in an accumulation of cells in G1, which then means that a rapid cell cycle is one where G1 is relatively short. I assume whatever question asked would be in reference to that.

 

[NickMB]

Sorry, hit the submit button twice by accident . I'll thus use this space to remind that eukaryotic and prokaryotic flagella are different. That can be a trick question on the MCAT. Remember that the main component of eukaryotic flagella is microtubules, while prokaryotic flagella are all about flagellin.

 

[freedom hater]

Why is a decrease in pH associated with increased CO2 levels.. doesn't CO2 turn into bicarbonate ions?.. and bicarbonate ions are basic

you cant trip on that or youll be missing a lot of points in general chemistry.

true, bicarbonate ion is basic, but the effect of H2CO3 is ACIDIC. H2CO3 is an ACID, not a base, it dissociates into a proton and its CONJUGATE BASE. Just because something has a conjugate base doesnt mean the effect is basic. If you thought that way, you could easily mistake a Base for an acid by thinking "well, NaOH breaks into Na+ and OH-, and Na+ is a cation..."

Don't be mislead by conjugates that appear upon dissociation, remember that the real molecule in question is H2CO3, an acid that lowers pH.

it might help to think about the relative reactability between the two. true, HCO3- is basic, but its much less reactive than H+, the acidic affect of H+ is much greater than that basic effect of the conjugate base, which is more stable. (though that line of thinking is not written anywhere, but ive been juggling that in my head as a way to mentally understand why molecules that dissociate into a base and an acid part are taken to be acidic or basic as a whole, and not just 'neutral'. )

 

[freedom hater]

1) Function is to bind to an enzyme and stabilize the active conformation of an enzyme. Enzymes are always oscillating between their inactive and active states so when the cofactor/coenzyme binds to it, it makes it easier for the substrate to complex with the enzyme.

2) Coenzymes are cofactors. Only difference is coenzyme are organic molecules, while cofactors are metal ions (inorganic).

3) Yes, NADH is a cofactor because it aids enzymes by giving them electrons.

Coenzyme - inorganic cofactor (generally accepted use).

wikipedia, and other definitions mirror that.

Cofactor - something that helps activate an enzyme. Some sources might define this as "everything that activates an enzyme", i.e. coenzymes, prosthetic groups, inorganic substances, etc.
others say cofactor is limited to 'inorganic'.

Your answer to his/her question seems to contradict itself:

1. NADH is organic, and you call it a cofactor (thus using the all-inclusive definition of cofactor)
2. You call coenzymes cofactors (same definition as before), THEN say that cofactors are inorganic. thats a direct contradiction.

"cofactors CAN be inorganic" may have been a better line.

 

[spoudaios]

Mutation in germ cells will be passed on to daughter cells, while mutation in somatic cells will not. Is this correct?

I thought during meiosis, all 23 chromosomes (paired with their homologues) undergo reduction division. The 1 pair is sex-chromosome and the 22 other pairs are autosomes/somatic chromosomes. If there are somatic mutations, will it be passed on to the offsprings then?

 

[freedom hater]

<from unnamed test prep review co. starting with K and ending with aplan>:
-From muskuloskeletal chapter:
"there are blood blood vessels, nerve fibers, and lymph in haversian canals innervating and vascularizing bone tissue"

-From Lymphatic System Questions:
Which of the following is NOT a function of the lymphatic system:

answer: "drainage of excess cerebrospinal fluid from brain"

Answer Reasoning:
"the lymphatic system does not drain excess fluid from the CNS, from superficial portions of skin, from deeper peripheral nerves, OR FROM BONE."

Please help.

is it "lymphatic vessels in SOME bone tissue, but not ALL" ?

 

[freedom hater]

Mutation in germ cells will be passed on to daughter cells, while mutation in somatic cells will not. Is this correct?

I thought during meiosis, all 23 chromosomes (paired with their homologues) undergo reduction division. The 1 pair is sex-chromosome and the 22 other pairs are autosomes/somatic chromosomes. If there are somatic mutations, will it be passed on to the offsprings then?

22 autosomes, 1 sex-chromosome. not 'somatic chromosomes'. those 22 chormosomes dont code for "just somatic cells' and the sex-chromosome isnt strictly for sex cells. all 23 chromosomes exist in every type of cell, somatic or germ.

a mutation in a somatic cell cannot be passed on because a somatic cell has nothing to do with the final zygote. if my muscle cell mutates into Hulk-like abilities, my kid wont have it because that muscle cell has nothing to do with fertilization. if a SPERM has a mutation and gets Hulk like abilities, thats another matter, because he could end up in the zygote.

 

[spoudaios]

### Okay. Let me restate this and please correct it if i am wrong.

So, ALL cells have 23 chromosomes (both somatic and germ cells (germ cells are in ovaries and testes)).
Out of these 23 pair chromosomes, 1 pair is sex chr and 22 pairs are autosomes.
Meiosis only involves germ cells. So, during meiosis, 23 pairs of chromosome in the germ cells line up and undergo reduction division.

If there is a mutation in any of these 23 pairs of chromosome (whether if it is on the autosomes or on the sex chromosomes, then it will be passed on to the offspring). Correct??????

On the cells other than germ cells, they only undergo mitosis and never get passed on to the daughter cells. So, let's say my biceps muscle chromosome which also has 23 pair of chromosome has a mutation in either the autosome or the sex chr, it will not be passed on. The reason is that it never undergoes meioses, thus no chance of going into the offspring.
Correct???????







a mutation in a somatic cell cannot be passed on because a somatic cell has nothing to do with the final zygote. if my muscle cell mutates into Hulk-like abilities, my kid wont have it because that muscle cell has nothing to do with fertilization. if a SPERM has a mutation and gets Hulk like abilities, thats another matter, because he could end up in the zygote.[/quote]

 

[SB100]

### Okay. Let me restate this and please correct it if i am wrong.

So, ALL cells have 23 chromosomes (both somatic and germ cells (germ cells are in ovaries and testes)).
Out of these 23 pair chromosomes, 1 pair is sex chr and 22 pairs are autosomes.
Meiosis only involves germ cells. So, during meiosis, 23 pairs of chromosome in the germ cells line up and undergo reduction division.

If there is a mutation in any of these 23 pairs of chromosome (whether if it is on the autosomes or on the sex chromosomes, then it will be passed on to the offspring). Correct??????

On the cells other than germ cells, they only undergo mitosis and never get passed on to the daughter cells. So, let's say my biceps muscle chromosome which also has 23 pair of chromosome has a mutation in either the autosome or the sex chr, it will not be passed on. The reason is that it never undergoes meioses, thus no chance of going into the offspring.
Correct???????







a mutation in a somatic cell cannot be passed on because a somatic cell has nothing to do with the final zygote. if my muscle cell mutates into Hulk-like abilities, my kid wont have it because that muscle cell has nothing to do with fertilization. if a SPERM has a mutation and gets Hulk like abilities, thats another matter, because he could end up in the zygote.

[/QUOTE]

If the mutation is on a somatic chromosome, and both parents have it (we'll say it's dominant here) then it will be passed on to offspring. It may or may not be passed on to offspring if it is sex-linked. For example, a father can't pass on a mutated X gene to his son because the son gets the Y chromosome from the father, with the X chromosome coming from the mother. Just draw out Punnett squares to help you out.

 

[spoudaios]

This is of course the mutation on one of the autosomes in the germ cells. (of the 22 autosomes in the germ cells we're talking about here, right?)

I want to clarify some definitions here:
1>. Each cell has 23 pair of chromosomes. 22 pair autosomes and 1 pair sex chromosomes.
2>. If we're talking about germ cells: 22 pairs are called autosomes and 1 pair is sex chromosomes. What will be the names for the 22 pairs in the somatic cells like cells in your gut and 1 pair of sex chromosome in your gut?




If the mutation is on a somatic chromosome, and both parents have it (we'll say it's dominant here) then it will be passed on to offspring. It may or may not be passed on to offspring if it is sex-linked. For example, a father can't pass on a mutated X gene to his son because the son gets the Y chromosome from the father, with the X chromosome coming from the mother. Just draw out Punnett squares to help you out.[/quote]

 

[freedom hater]

I want to clarify some definitions here:
1>. Each cell has 23 pair of chromosomes. 22 pair autosomes and 1 pair sex chromosomes.

Yes.

2>. If we're talking about germ cells: 22 pairs are called autosomes and 1 pair is sex chromosomes. What will be the names for the 22 pairs in the somatic cells like cells in your gut and 1 pair of sex chromosome in your gut?

The same. Gut cells = Somatic cells, every cell has 22 autosomes, and 1 sex chromosome. In germ line and somatic cells, there are 22 PAIRS of autosomes, and 1 PAIR of sex chromosome. in gametes there are 22 autosomes (not in pairs) and 1 sex chromosome (not in pairs).


now, someone please answer my questions

 

[abdrew]

Thanks, MollyMalone (and QofQuimica for letting her know). It's a lot clear in my mind now. However, I am just a bit confused about the presence of leukocytes in circulatory system and lymphatic system. Do both systems always have all leukocytes (lymphocytes, monocytes, megakaryotes, and other granular leukocytes such as neutrophils, basophils and eosinophils)? I realize all blood cells arise/differentiate from the bone marrow but where do granular leukocytes mature?
Also, if circulatory system contains leukocytes, what's the point of having a lymphatic system? I mean leukocyts in circulatory system will eliminate infecitons and other infective substances. Is it because circulatory sytem can't eliminate infections in interstitial fluid so lymphatic is present mainly for that purpose? Your explanation of the various purposes of lymphatic system is very concise and to the point, but I am just curious why we need lymphatic system if blood carries leukocytes (Does blood only carry T/B-cells+macrophages, or does it carry complete set of leukocytes?). Do lymphatic and circulatory system carry different leukocytes? Sorry for the long post but I really appreciate your help!

The lymphatic system removes excess fluids from body tissues, absorbs fatty acids, transports fat to the circulatory system, produces and transports white blood cells in immune responses. Lymph is actually the blood plasma that leaks from capillaries and has diffused into lymphatic organs for processing before returning to the circulatory system, which serves as the vehicle of white blood cells. Damage or interference in the function of lymphatic organs can result in bodily swelling. Since the organs are not functioning correctly, they are not absorbing the interstitial fluid that would become lymph when absorbed. Thus, the fluid just continues to collect in the body, causing it to swell. A similar phenomena occurs when there is a blockage in lymphatic veins. Problems such as these occur for a number of reasons, but the most common ones today are usually associated with certain types of cancer.

 

[Mandek]

Should we memorize all the amino acids for the MCAT? What sort of detail do we need to know (about amino acids) for the purpose of the MCAT? Thanks.

 

[armybound]

Should we memorize all the amino acids for the MCAT? What sort of detail do we need to know (about amino acids) for the purpose of the MCAT? Thanks.

I think it's good to know which are basic and which are acidic, and be able to estimate the isoelectric point on them.

e.g. at pH 7, what is the expected net charge on lysine?

 

[phospho]

would very much appreciate it if someone could tell me what exactly chloride ions do in our body.

For example, how does Cl- affect voltage across membrane? how is it excreted from kidney? Also, I can't seem to grasp the "chloride shift".

thank you

 

[tncekm]

would very much appreciate it if someone could tell me what exactly chloride ions do in our body.

For example, how does Cl- affect voltage across membrane? how is it excreted from kidney? Also, I can't seem to grasp the "chloride shift".

thank you

The chloride shift is just a way for the body to keep a balanced charge inside and outside of the cells.

Because carbonic anhydrase, which catalyzes the reaction CO&#8322; + H&#8322;O --> H&#8322;CO&#8323; <--> H&#8314; + HCO&#8323;&#8315;, exists inside of the RBC's the body needs to bring HCO&#8323;&#8315; into the RBC. However, if it does this without altering anything else the charge across the membrane would get drastically altered, and most likely, there would quickly be far too much negative charge for bicarbonate to make it into the cell. So, the solution to this problem is to trade a chloride ion for a bicarbonate ion each time bicarbonate needs to enter or leave the cell; the result: the charge across the membrane stays balanced.

As far as what chloride ions do, I'm not aware of any MCAT specific stuff aside from the chloride shift--but that's pretty important to our physiology!

 

[phospho]

The chloride shift is just a way for the body to keep a balanced charge inside and outside of the cells.

Because carbonic anhydrase, which catalyzes the reaction CO&#8322; + H&#8322;O --> H&#8322;CO&#8323; <--> H&#8314; + HCO&#8323;&#8315;, exists inside of the RBC's the body needs to bring HCO&#8323;&#8315; into the RBC. However, if it does this without altering anything else the charge across the membrane would get drastically altered, and most likely, there would quickly be far too much negative charge for bicarbonate to make it into the cell. So, the solution to this problem is to trade a chloride ion for a bicarbonate ion each time bicarbonate needs to enter or leave the cell; the result: the charge across the membrane stays balanced.

As far as what chloride ions do, I'm not aware of any MCAT specific stuff aside from the chloride shift--but that's pretty important to our physiology!

very nice, thank you...

should we care about how the Cl- ions came on the RBC in the first place or what happens to them after they are unloaded from the RBC?

Also, do you have any idea how Cl- might affect or contribute to the cell membrane voltage? Is it internalized? does it leak in/out?

 

[tncekm]

I've never seen Chloride ion suggested to play a substantial role in the resting potential of a membrane, so I wouldn't worry about it.

And aside from the fact that it is used to keep the membrane potential in RBC's balanced (because they've got to deal with the conversion of CO2 to bicarbonate and H+, etc) I don't think there is any other MCAT importance--and if there is, I didn't know about it

 

[phospho]

I've never seen Chloride ion suggested to play a substantial role in the resting potential of a membrane, so I wouldn't worry about it.

And aside from the fact that it is used to keep the membrane potential in RBC's balanced (because they've got to deal with the conversion of CO2 to bicarbonate and H+, etc) I don't think there is any other MCAT importance--and if there is, I didn't know about it

sounds good, thank you very much

 

[tncekm]

Anytime!

 

[phospho]

How does the neurotransmitter travel across the cleft? is it diffusion, brownian movement, or both? I'm getting conflicting results on google. Also, is there a better explanation for what brownian movement is - other than that it's the "random movement of molecules"?

thanks