the main usable product of the TCA cycle is

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The main, usable product of the tricarboxylic acid cycle is

Energy
Carbon dioxide
The reduced coenzymes NADH+H+ and FADH2
Malate
 
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I have to go with

The reduced coenzymes NADH+H+ and FADH2

These are used by the ETC to generate ATP...
 
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Don't forget GTP produced by the single substrate-level phosphorylation !
 
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yup, like i was saying, he's usually right...i've gotten some great info from Vihsadas
 
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**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:
 
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Vihsadas said:
Yeah, I was even thinking of the 'malate-aspartate' shuttle to rationalize why malate was one of the answer choices (o_0).
Click to expand...

See...that's exactly what I'm talking about. How many people remember the malate-aspartate shuttle? That's bad a$$!
 
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Mandek said:
**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:
Click to expand...

And I believe bluemonkey got a 14 on PS, while Vihsadas got a 14 on BS. haha! perfect 🙂
 
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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!
 
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Mandek said:
malate-aspartate shuttle takes places during the Krebs cyble? What does it do exactly?
Click to expand...

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...
 
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And furthermore why prokaryotes produce 38 ATP per molecule of glucose, while eukaryotes only produce 36 ATP per molecule of glucose...
 
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bluemonkey said:
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...
Click to expand...

produced in glycolysis? thought it was krebs/TCA cycle>?
 
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Mandek said:
produced in glycolysis? thought it was krebs/TCA cycle>?
Click to expand...

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

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
 
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Vihsadas said:
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
Click to expand...

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?)
 
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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.
 
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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...
 
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Mandek said:
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)
Click to expand...

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! 🙂
 
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bluemonkey said:
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...
Click to expand...
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!
 
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Vihsadas said:
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.
Click to expand...

But this will make you a better person (in some sick SDN way).
 
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Vihsadas said:
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! 🙂
Click to expand...

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?
 
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Vihsadas said:
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!
Click to expand...


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
 
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Mandek said:
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?
Click to expand...

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...
 
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Mandek said:
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?
Click to expand...

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 😛 :
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. 😛
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.
 
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Vihsadas said:
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 😛 :
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. 😛
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.
Click to expand...

Don't forget about the oxygen debt...
 
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bluemonkey said:
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...
Click to expand...

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?
 
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Mandek said:
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?
Click to expand...

For your purposes. Yes. haha.
But notice that Malate is one of the intermediates in the TCA cycle. 😉
 
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Vihsadas said:
For your purposes. Yes. haha.
But notice that Malate is one of the intermediates in the TCA cycle. 😉
Click to expand...

Yes, Malate is the intermediate in the TCA cyle (does this Malate come from mal-asp shuttle?)
 
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Mandek said:
Yes, Malate is the intermediate in the TCA cyle (does this Malate come from mal-asp shuttle?)
Click to expand...

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.
 
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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?
 
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Mandek said:
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?
Click to expand...

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.
 
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Vihsadas said:
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.
Click to expand...

Thanks Vihsadas! You've been a great help! 👍

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
 
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Mandek said:
Thanks Vihsadas! You've been a great help! 👍

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
Click to expand...

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.
 
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Vihsadas said:
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.
Click to expand...

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).
 
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Mandek said:
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?
Click to expand...

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.
 
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Vihsadas said:
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.
Click to expand...

aha! Makes sense!!!! 👍

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.
 
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