The main, usable product of the tricarboxylic acid cycle is

Energy
Carbon dioxide
The reduced coenzymes NADH+H+ and FADH2
Malate

EDIT: Yikes. You gusy are right. Totally read 'ETC'.

I have to go with

The reduced coenzymes NADH+H+ and FADH2

These are used by the ETC to generate ATP...

Don't forget GTP produced by the single substrate-level phosphorylation !

I think it is option C. The coenzymes make more ATP through the ETC later on.

The energy (ATP) produced by the TCA is minimal compared to the ETC.

EDIT: Yikes. You gusy are right. Totally read 'ETC'.

Thank God. We now know that 40S'ers are also human :)

EDIT: Yikes. You gusy are right. Totally read 'ETC'.

No worries...


You've been right the other 99.99% of the time...:laugh:

Thank God. We now know that 40S'ers are also human :)
Haha. We certainly are. Late night, 3 exams in the next two days...and what am I doing? attempting to answer questions in the MCAT forum. :lol:

No worries...


You've been right the other 99.99% of the time...:laugh:

he had the right thought process on the question but just misread the question.

yup, like i was saying, he's usually right...i've gotten some great info from Vihsadas

**NOTE TO SELF

For BS advice, go to bluemonkey (scored a perfect 15 on BS)
For PS advice, go to Vihsadas (scored a perfect 15 on PS)

:clap:

he had the right thought process on the question but just misread the question.

Yeah, I was even thinking of the 'malate-aspartate' shuttle to rationalize why malate was one of the answer choices (o_0).

Yeah, I was even thinking of the 'malate-aspartate' shuttle to rationalize why malate was one of the answer choices (o_0).

See...that's exactly what I'm talking about. How many people remember the malate-aspartate shuttle? That's bad *****!

**NOTE TO SELF

For BS advice, go to bluemonkey (scored a perfect 15 on BS)
For PS advice, go to Vihsadas (scored a perfect 15 on PS)

:clap:

And I believe bluemonkey got a 14 on PS, while Vihsadas got a 14 on BS. haha! perfect :)

And I believe bluemonkey got a 14 on PS, while Vihsadas got a 14 on BS. haha! perfect :)

Wow, you're keeping track of all of us!!!:laugh:

See...that's exactly what I'm talking about. How many people remember the malate-aspartate shuttle? That's bad *****!

malate-aspartate shuttle takes places during the Krebs cyble? What does it do exactly?

Wow, you're keeping track of all of us!!!:laugh:

Got to...lol...I would rather learn from people who've "been there, done that"

I took enough upper level bio and even took biochem, how come I never even heard of malate-asp shuttle? lol..you guys are insane!

malate-aspartate shuttle takes places during the Krebs cyble? What does it do exactly?

It essentially transports the NADH produced in glycolysis into the ETC. The inner mitochondrial membrane is not permeable to NADH or H+, hence the need for a special "shuttle." This is why the NADH in glycolysis only produce 2 ATP while all (from pyruvate decarbox & ETC) the other NADH produce 3 ATP...

And furthermore why prokaryotes produce 38 ATP per molecule of glucose, while eukaryotes only produce 36 ATP per molecule of glucose...

It essentially transports the NADH produced in glycolysis into the ETC. The inner mitochondrial membrane is not permeable to NADH or H+, hence the need for a special "shuttle." This is why the NADH in glycolysis only produce 2 ATP while all (from pyruvate decarbox & ETC) the other NADH produce 3 ATP...

produced in glycolysis? thought it was krebs/TCA cycle>?

produced in glycolysis? thought it was krebs/TCA cycle>?

Nope, you (we collectively) produce 2 molecules per molecule of glucose. Glycolysis takes place in the cytoplasm. Everything else is in the mitochondria...

Nope, you (we collectively) produce 2 molecules per molecule of glucose. Glycolysis takes place in the cytoplasm. Everything else is in the mitochondria...

oh ok..I see..get it now

I am just having trouble understanding where the "malate-asp shuttle" fits in. By glycolysis, you get pyruvate --> then acetyl coA (krebs cycle begins)...then you get NADH+ and FADH2..then goes through ETC to make ATP..right? Where does mal-asp shuttle fit into all this? thanks for clarifying. just want to clear up the confusion.

I am just having trouble understanding where the "malate-asp shuttle" fits in. By glycolysis, you get pyruvate --> then acetyl coA (krebs cycle begins)...then you get NADH+ and FADH2..then goes through ETC to make ATP..right? Where does mal-asp shuttle fit into all this? thanks for clarifying. just want to clear up the confusion.

Okay so glycolysis happens in the cytosol, and the TCA happens inside the mitochondria. The NADH produced by glycolysis is impermeable to the mito membranes. So without a shuttling mechanism, the NADH that you make in glycolysis would not get into the mitochondria.

The malate aspartate shuttle allows for the NADH to transfer its reducing equivalents to inside the mitochondria.
It's actually a pretty cool mechanism because no NADH is actually transported, rather, the electrons from NADH are moved inside the mitochondria to another, different NAD molecule by the interconversion of aspartate to malate on the outside and then malate to aspartate on the inside.

So, asparate -> malate outside the mitochondria, which is catalyzed by NADH -> NAD+, then the malate physically crosses the mito membrane. On the inside that malate is then converted back into asparate by the reverse reaction: Malate -> Aspartate, while using NAD as a cofactor creating NADH (inside mito).

So without actually making NADH cross the mito membrane, the reducing equivalents are still transferred to inside the mitochondria. :)

EDIT: Wiki has an entry on it with a good diagram - http://en.wikipedia.org/wiki/Image:Malateaspartateshuttle.png

Okay so glycolysis happens in the cytosol, and the TCA happens inside the mitochondria. The NADH produced by glycolysis is impermeable to the mito membranes. So without a shuttling mechanism, the NADH that you make in glycolysis would not get into the mitochondria.

The malate aspartate shuttle allows for the NADH to transfer its reducing equivalents to inside the mitochondria.
It's actually a pretty cool mechanism because no NADH is actually transported, rather, the electrons from NADH are moved inside the mitochondria to another, different NAD molecule by the interconversion of aspartate to malate on the outside and then malate to aspartate on the inside.

So, asparate -> malate outside the mitochondria, which is catalyzed by NADH -> NAD+, then the malate physically crosses the mito membrane. On the inside that malate is then converted back into asparate by the reverse reaction: Malate -> Aspartate, while using NAD as a cofactor creating NADH (inside mito).

So without actually making NADH cross the mito membrane, the reducing equivalents are still transferred to inside the mitochondria. :)

EDIT: Wiki has an entry on it with a good diagram - http://en.wikipedia.org/wiki/Image:Malateaspartateshuttle.png

Oh ok. I see. So, mal-asp shuttle goes through this mechanism just to get NADH+ across.... and what would the purpose of this NADH+ be? To get Krebs/TCA cycle started? (in order to go from pyruvate to acetyl coA..NADH+ is needed?)

Is this info about mal-asp shuttle useful on the MCAT? or we just dont need it for the purpose of the mcat? Thanks Vihsadas for clearing it up. Makes me understand it alot better and have a clearer picture. By the way, where did you learn this mal-asp shuttle? Biochem? or was it part of your MCAT review? I see that EK doesnt mention mal-asp shuttle ..it just has a diagram which shows NADH+ is transported across.

I remember covering the malate-aspartate shuttle in biochem. It's highly unlikely that you would see a question on the MCAT specifically covering this mechanism. You would much more likely see a question asking why eukaryotes only produce 36 ATP/glucose while prokaryotes produce 38 ATP/glucose...

Oh ok. I see. So, mal-asp shuttle goes through this mechanism just to get NADH+ across.... and what would the purpose of this NADH+ be? To get Krebs/TCA cycle started? (in order to go from pyruvate to acetyl coA..NADH+ is needed)

No, wait a second. For the decarboxylation of pyruvate to Acetyl-CoA, NAD+ is needed, not NADH (I think). I think this decarboxylation reaction goes:

Pyruvate (via CO2 + NAD+ + CoA-SH) ===> Acetyl-CoA + NADH+H+

So the NADH that comes in from glycolysis isn't used for pyruvate -> acetyl-CoA, but it can be used for any other purpose that NADH is needed, including making energy via the ETC! :)

I remember covering the malate-aspartate shuttle in biochem. It's highly unlikely that you would see a question on the MCAT specifically covering this mechanism. You would much more likely see a question asking why eukaryotes only produce 36 ATP/glucose while prokaryotes produce 38 ATP/glucose...
Yeah I should have mentioned this.

The malate-asparate shuttle is not required for the MCAT. The previous information is completely for your own edification.

***EDIT: While the Malate-Aspartate Shuttle is NOT MCAT material, the reaction from pyruvate ==> Acetyl-CoA IS MCAT material!

Yeah I should have mentioned this.

The malate-asparate shuttle is not required for the MCAT. The previous information is completely for your own edification.

But this will make you a better person (in some sick SDN way).

No, wait a second. For the decarboxylation of pyruvate to Acetyl-CoA, NAD+ is needed, not NADH (I think). I think this decarboxylation reaction goes:

Pyruvate (via CO2 + NAD+ + CoA-SH) ===> Acetyl-CoA + NADH+H+

So the NADH that comes in from glycolysis isn't used for pyruvate -> acetyl-CoA, but it can be used for any other purpose that NADH is needed, including making energy via the ETC! :)

Oops yes your right, I meant NAD+ (so this NAD+ is totally different)

For the purpose of ETC, doesnt Krebs/TCA cycle produce NADH for it to be used for ETC? why would NADH from glycolysis be needed if krebs cycle produces it anyway?

Yeah I should have mentioned this.

The malate-asparate shuttle is not required for the MCAT. The previous information is completely for your own edification.

***EDIT: While the Malate-Aspartate Shuttle is NOT MCAT material, the reaction from pyruvate ==> Acetyl-CoA IS MCAT material!


I understand that we don't need to know mal-asp shuttle for the MCAT, but it helps understand better about glycolysis/krebs cycle/ETC

Oops yes your right, I meant NAD+ (so this NAD+ is totally different)

For the purpose of ETC, doesnt Krebs/TCA cycle produce NADH for it to be used for ETC? why would NADH from glycolysis be needed if krebs cycle produces it anyway?

It's not necessarily a matter of need. It's more a matter of why would you waste the potential energy from the NADH's produced by glycolysis. You're talking an extra 4 ATP/molecule of glucose...It's over an extra 10% energy production...

Oops yes your right, I meant NAD+ (so this NAD+ is totally different)

For the purpose of ETC, doesnt Krebs/TCA cycle produce NADH for it to be used for ETC? why would NADH from glycolysis be needed if krebs cycle produces it anyway?

Well its just another source of energy...
Aerobic metabolism (TCA) is primarily used when O2 is present and Anaerobic metabolism (glycolysis) is primarliy used when O2 conditions are low, such as exercise. Why waste the NADH? You need glycolysis to make Acetyl-CoA anyway. :)

NON MCAT MATERIAL TO FOLLOW :p :
One use of the Anaerobic energy production system is that, while the TCA produces MORE ATP per glucose, Glycolysis can produce it alot faster. In exercise, energy consumption very quickly saturates the speed at which the TCA can churn out ATP. Instead the Anaerobic system (glycolysis) steps in and can produce ATP much faster. This produces Lactate, because the pyruvate that is made by glycolysis must be fermented to create NAD+. This NAD+, remember, is required for Glycolysis to continue. So during exercise, glycolysis is self-propagating. It uses NAD+, makes NADH and ATP, and then through fermentation to lactate, it regenerates its NAD+ so glycolysis can continue. This fermentation to lactate is referred to as the 'oxygen debt'. This is because when O2 becomes present, the lactate can be reconverted to pyruvate, and then be used in the TCA. The lactate buildup is why you get sore muscles. :p
There is also the Creatine-Phosphate ATP buffer system to give you ATP for the first few seconds of exercising but I wouldn't worry about that.

Well its just another source of energy...
Aerobic metabolism (TCA) is primarily used when O2 is present and Anaerobic metabolism (glycolysis) is primarliy used when O2 conditions are low, such as exercise. Why waste the NADH? You need glycolysis to make Acetyl-CoA anyway. :)

NON MCAT MATERIAL TO FOLLOW :p :
One use of the Anaerobic energy production system is that, while the TCA produces MORE ATP per glucose, Glycolysis can produce it alot faster. In exercise, energy consumption very quickly saturates the speed at which the TCA can churn out ATP. Instead the Anaerobic system (glycolysis) steps in and can produce ATP much faster. This produces Lactate, because the pyruvate that is made by glycolysis must be fermented to create NAD+. This NAD+, remember, is required for Glycolysis to continue. So during exercise, glycolysis is self-propagating. It uses NAD+, makes NADH and ATP, and then through fermentation to lactate, it regenerates its NAD+ so glycolysis can continue. This fermentation to lactate is referred to as the 'oxygen debt'. This is because when O2 becomes present, the lactate can be reconverted to pyruvate, and then be used in the TCA. The lactate buildup is why you get sore muscles. :p
There is also the Creatine-Phosphate ATP buffer system to give you ATP for the first few seconds of exercising but I wouldn't worry about that.

Don't forget about the oxygen debt...

It's not necessarily a matter of need. It's more a matter of why would you waste the potential energy from the NADH's produced by glycolysis. You're talking an extra 4 ATP/molecule of glucose...It's over an extra 10% energy production...

Oh ok. So its like the more NADH, the better for ETC == that way it produces more ATP/energy?

If I am understanding this correctly, there is NO connection between the mal-asp shuttle and krebs/TCA cycle? Mal-asp shuttle simply gets NADH across for other purposes (for example, for it to be used for ETC to make more ATP). Am I understanding this right?

Don't forget about the oxygen debt...

Its' there! It's there! Read the fine print. :laugh:

Oh ok. So its like the more NADH, the better for ETC == that way it produces more ATP/energy?

If I am understanding this coorectly, there is NO connection between the mal-asp shuttle and krebs/TCA cycle? Mal-asp shuttle simply gets NADH across for other purposes (for example, for it to be used for ETC to make more ATP). Am I understanding this right?

For your purposes. Yes. haha.
But notice that Malate is one of the intermediates in the TCA cycle. ;)

Its' there! It's there! Read the fine print. :laugh:

sorry!!! it's my bed time!!!:laugh:

For your purposes. Yes. haha.
But notice that Malate is one of the intermediates in the TCA cycle. ;)

Yes, Malate is the intermediate in the TCA cyle (does this Malate come from mal-asp shuttle?)

Yes, Malate is the intermediate in the TCA cyle (does this Malate come from mal-asp shuttle?)

See, its not that one things comes from this, and one thing comes from that. It's ALL INTERCONNECTED! :)
This malate is the same malate as all malate! If you take biochem you'll see that these intermediates aren't locked up in either the TCA cycle or the malate-asparate shuttle, or whatever else. There is a dynamic equilibrium between all the processes that use the different molecules. It's all connected, and everything affects everything else.

ah, this diagram also explains nicely.

http://www.med.unibs.it/~marchesi/malate.html

Also, why 36 net ATP in Euk vs 38 in prok? is it because of electrons from the NADH produced from pyruvate decarboxylation do not have to be transported across the mitochondrial membrane in prok but since this happens in euk, there is a loss of 2 ATP?

Also, why 36 net ATP in Euk vs 38 in prok? is it because of electrons from the NADH produced from pyruvate decarboxylation do not have to be transported across the mitochondrial membrane in prok but since this happens in euk, there is a loss of 2 ATP?

That is correct. :)
Good logic! That'll serve you well on the MCAT.

For some reason, when NADH is transported from the cytosol to the mitochondria, it can't enter the ETC at the first reducing step. Instead it only enters at the second step, and you only get 2ATP per NADH from glycolysis instead of the normal 3ATP from NADH that you get from the TCA.

That is correct. :)
Good logic! That'll serve you well on the MCAT.

For some reason, when NADH is transported from the cytosol to the mitochondria, it can't enter the ETC at the first reducing step. Instead it only enters at the second step, and you only get 2ATP per NADH from glycolysis instead of the normal 3ATP from NADH that you get from the TCA.

Thanks Vihsadas! You've been a great help! :thumbup:

I was kind of confused about this question in EK bio book

Heart and liver cells can produce more ATP for each molecule of glucose than other cells in the body. This is most likely results of:

A. a more efficient ATP synthase on the outer mitochondrial membrane
B. an additional turn of the Kreb's Cycle for each glucose molecule
C. a more efficient mechanism for moving NADH produced in glycolysis into the mitochondrial matrix
D. production of additional NADH by the citric acid cycle




How are you supposed to reason this one, I was confused between two choices

Thanks Vihsadas! You've been a great help! :thumbup:

I was kind of confused about this question in EK bio book

Heart and liver cells can produce more ATP for each molecule of glucose than other cells in the body. This is most likely results of:

A. a more efficient ATP synthase on the outer mitochondrial membrane
B. an additional turn of the Kreb's Cycle for each glucose molecule
C. a more efficient mechanism for moving NADH produced in glycolysis into the mitochondrial matrix
D. production of additional NADH by the citric acid cycle




How are you supposed to reason this one, I was confused between two choices

Well lets go through your thinking. I'll tell you what I think the answer is right now, but reason out why you eliminated the answers you did and why you narrowed it down to the two that you chose. I would guess that this answer is C.

Well lets go through your thinking. I'll tell you what I think the answer is right now, but reason out why you eliminated the answers you did and why you narrowed it down to the two that you chose. I would guess that this answer is C.

You are right the answer is C indeed. I knew A was wrong (because the A says "outer", ATP synthase in in the inner mitochondrial membrane) and I also eliminated D because there is really no extra NADH made for a cycle (i.e no change in the way cycle works).

How did you reason this?

I was thinking it was either B or C. Choice A was wrong (for reason listed above) and D doesnt sound right (it would change the whole cycle if "extra" NADH was produced).

You are right the answer is C indeed. I knew A was wrong (because the A says "outer", ATP synthase in in the inner mitochondrial membrane) and I also eliminated D because there is really no extra NADH made for a cycle (i.e no change in the way cycle works).

How did you reason this?

You're are right about A. That's definitely wrong because it's 'outer'.

D, again, you're right. If the TCA were to produce some more NADH by some magic, it wouldn't be the TCA anymore! You would have to change some of the steps in the TCA to make this happen, so this is wrong.

Now, about B. When we are talking about how glucose goes through the metabolic cycles, we are looking at the oxidation of carbons. This is what is important. Thus, it is the number of carbons that we are tracking. Glucose has 6 carbons, which get broken down into two 3 carbon Acetyl-CoA, which go into the TCA cycle for two turns. For there to be more turns of the TCA, you would have to use a molecule with more carbons. Thus, the carbons from glucose can only generate enough impetus to cycle the TCA twice, you can never get more turns out of it.

C on the other hand seems reasonable. There are multiple ways that the body shuttles NADH into the mito matrix (the Mal-Asp shuttle being one of them). If there was a more efficient shuttle, then its feasible that the NADH from glycolysis could be made to enter the ETC at the first complex, instead of the second complex (like normal). If this were to happen you'd get one more ATP per glycolytic NADH.

Thus, C seems the most reasonable.

You're are right about A. That's definitely wrong because it's 'outer'.

D, again, you're right. If the TCA were to produce some more NADH by some magic, it wouldn't be the TCA anymore! You would have to change some of the steps in the TCA to make this happen, so this is wrong.

Now, about B. When we are talking about how glucose goes through the metabolic cycles, we are looking at the oxidation of carbons. This is what is important. Thus, it is the number of carbons that we are tracking. Glucose has 6 carbons, which get broken down into two 3 carbon Acetyl-CoA, which go into the TCA cycle for two turns. For there to be more turns of the TCA, you would have to use a molecule with more carbons. Thus, the carbons from glucose can only generate enough impetus to cycle the TCA twice, you can never get more turns out of it.

C on the other hand seems reasonable. There are multiple ways that the body shuttles NADH into the mito matrix (the Mal-Asp shuttle being one of them). If there was a more efficient shuttle, then its feasible that the NADH from glycolysis could be made to enter the ETC at the first complex, instead of the second complex (like normal). If this were to happen you'd get one more ATP per glycolytic NADH.

Thus, C seems the most reasonable.

aha! Makes sense!!!! :thumbup:

so, choice B and D are wrong for "similar" reasons? i.e you cannot produce more NADH (change the cycle) nor you can do more cycles which will affect the system.

aha! Makes sense!!!! :thumbup:

so, choice B and D are wrong for "similar" reasons? i.e you cannot produce more NADH (change the cycle) nor you can do more cycles which will affect the system.

Yes that's right. This problem exemplifies the trickiness that the MCAT can present. In B and D its suggesting a fundamental change to the cycle, which by the wording of the question, would make the answers 'false'. C, however, does not say 'make the malate aspartate shuttle more efficient', or 'transport an extra NADH via the malate-aspartate shuttle,' which would also make answer C 'false'. It suggests, instead, an entirely new shuttle, which is more efficient, making this answer 'plausible'.
This is how the MCAT tests 'logic' and 'knowledge'. On this problem if you had the 'knowledge' of information that is extranneous to the MCAT but related to this in real life, you would be able to answer the question. However, if you didn't have that knowledge, and only had the knowledge of your MCAT concept review books by using the 'logic' that I outlined you could still figure it out.

Yes that's right. This problem exemplifies the trickiness that the MCAT can present. In B and D its suggesting a fundamental change to the cycle, which by the wording of the question, would make the answers 'false'. C, however, does not say 'make the malate aspartate shuttle more efficient', or 'transport an extra NADH via the malate-aspartate shuttle,' which would also make answer C 'false'. It suggests, instead, an entirely new shuttle, which is more efficient, making this answer 'plausible'.
This is how the MCAT tests 'logic' instead of 'knowledge'. On this problem if you had the 'knowledge' of information that is extranneous to the MCAT but related to this in real life, you could still answer the question. However, if you didn't have that knowledge, and only had the knowledge of your MCAT concept review books by using the 'logic' that I outlined you could still figure it out.

wow....yes thanks...I truly believe that the more practice MCAT problems you do, the more you find out how MCAT tests you and you get the right thought process which will in turn help you on real MCAT. Even though questions wont be the same, it still would be very helpful to know what kind of questions are asked on MCAT, and thus the more practice you do, the closer it brings you to your goal (of what set goal one has for the MCAT score).

wow....yes thanks...I truly believe that the more practice MCAT problems you do, the more you find out how MCAT tests you and you get the right thought process which will in turn help you on real MCAT. Even though questions wont be the same, it still would be very helpful to know what kind of questions are asked on MCAT, and thus the more practice you do, the closer it brings you to your goal (of what set goal one has for the MCAT score).

That's exactly right. At a certain point, answering some questions almost becomes a 'learned art'. You know, that question you just asked, when I first glanced at each answer I just kinda 'felt' that C seemed more right, and the others were more wrong. Then when I sat down to think about it, I rationalized why. This is pure practice. You practice the problems more and more, you'll begin to develop what I call 'MCAT intuition'.

That's exactly right. At a certain point, answering some questions almost becomes a 'learned art'. You know, that question you just asked, when I first glanced at each answer I just kinda 'felt' that C seemed more right, and the others were more wrong. Then when I sat down to think about it, I rationalized why. This is pure practice. You practice the problems more and more, you'll begin to develop what I call 'MCAT intuition'.

Do you think this also applies to the VR section? Did you notice similar traps thrown on the MCAT to the practice exams (in verbal that is)?

Do you think this also applies to the VR section? Did you notice similar traps thrown on the MCAT to the practice exams (in verbal that is)?

Yes definitely. It applies more so to the VR. In the AAMC practice exams (which can be MUCH easier than your real exam if you get a bad exam day!!) a large part of the reason I was scoring consistently in the 13-15 was because I had very good intuition about the problems. Check out my VR tips. They are somewhere on this forum. :p

As a corollary to VR, I'd say that you really, really need to make sure that you can do the practice AAMC exams in 6.5-7mins per passage rather than 8. If you have 10-15mins left over during your initial run through on the AAMC exams, you should be ok. Just be AWARE that your real VR *Could* be longer, harder, and more confusing than the AAMC practices.

Yes definitely. It applies more so to the VR. In the AAMC practice exams (which can be MUCH easier than your real exam if you get a bad exam day!!) a large part of the reason I was scoring consistently in the 13-15 was because I had very good intuition about the problems. Check out my VR tips. They are somewhere on this forum. :p

As a corollary to VR, I'd say that you really, really need to make sure that you can do the practice AAMC exams in 6.5-7mins per passage rather than 8. If you have 10-15mins left over during your initial run through on the AAMC exams, you should be ok. Just be AWARE that your real VR *Could* be longer, harder, and more confusing than the AAMC practices.

Yes, thanks!!!!! I always wanted to ask you: how did you feel on each section after you walked out of the real MCAT? Were you pretty confident/sure about getting 13-15's on PR and BS, and how did you feel on VR. I know you said VR was tough, but alot of times I've heard people say they almost wanted to void/cancel their scores after walking out of the real MCAT but it turned out to be a 32-33+ for them ....weird

Yes, thanks!!!!! I always wanted to ask you: how did you feel on each section after you walked out of the real MCAT? Were you pretty confident/sure about getting 13-15's on PR and BS, and how did you feel on VR. I know you said VR was tough, but alot of times I've heard people say they almost wanted to void/cancel their scores after walking out of the real MCAT but it turned out to be a 32-33+ for them ....weird
Yeah. It was similar for me. After my PS (first section) I remember walking out to get a candy bar and thinking "Holy crap. I think I just got everything right." After walking out of my VR I was completely shaken. Seriously one of the most horrifying experiences of my life. haha. I had never taken any practice test that hard. That VR section kicked my butt. I felt like voiding my test after that to be certain...I feel like if I had taken it in August, I actually maybe WOULD have voided my score (Imagine that!).
After BS, I remember thinking "Oh crap. I think I got them all rig...oh wait. Damnit. I missed one."

So on BS and PS I knew I got a 14 and a 15, on VR, I seriously thought I got a 7 or 8. I feel like if that section was curved like the practice MCATs I would have!

Yeah. It was similar for me. After my PS (first section) I remember walking out to get a candy bar and thinking "Holy crap. I think I just got everything right." After walking out of my VR I was completely shaken. Seriously one of the most horrifying experiences of my life. haha. I had never taken any practice test that hard. That VR section kicked my butt. I felt like voiding my test after that to be certain...I feel like if I had taken it in August, I actually maybe WOULD have voided my score (Imagine that!).
After BS, I remember thinking "Oh crap. I think I got them all rig...oh wait. Damnit. I missed one."

So on BS and PS I knew I got a 14 and a 15, on VR, I seriously thought I got a 7 or 8. I feel like if that section was curved like the practice MCATs I would have!

I guess fair enough, if you found VR hard, then it really was hard and curve did justice...in order to get a 10 on normal curve, you have to get 28 right out of 40 i believe. do you think its possible in a VR section hard like that (the one you had on real thing) to get 15-17 wrong and still end up with a 10 since it was harder? haha

no idea how AAMC comes up with a "curve"

It essentially transports the NADH produced in glycolysis into the ETC. The inner mitochondrial membrane is not permeable to NADH or H+, hence the need for a special "shuttle." This is why the NADH in glycolysis only produce 2 ATP while all (from pyruvate decarbox & ETC) the other NADH produce 3 ATP...

Just to help illuminate "why" NADH from Glycolysis and FADH2 only produce, the NADH produced by Glycolysis is not delivered to the NADH Dehydrogenase complex, its skips it, as does FADH2. NADH from the krebs cycle does go through the NADH dehydrogenase complex. So, normally NADH hits 3/3 complexes and FADH2 and NADH from glycolysis only get 2/3, therefore, they result in 2/3 the ATP.
http://www.columbia.edu/cu/biology/courses/c2005/handouts/etccomplexes.jpg