Four Questions on Cellular Respiration

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vertciel
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Four Questions on Cellular Respiration

Post by vertciel » Sat Sep 27, 2008 3:03 pm

Hello everyone:

I am having some trouble with the following questions and would appreciate help.

Thank you!

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1. True or False: Oxidative phosphorylation produces approximately three ATP for every NADH that is oxidised.

I guessed True, but do not understand why it is so. I have calculated that a total of 10 NADH is produced from 1 glucose molecule, but from where does the 3:1 ratio of ATP:NADH come?

2. When glucose is oxidised to carbon dioxide and water, approximately 40% of its energy is transferred to:

a) heat b) ATP c) acetyl CoA d) water e) Citric acid cycle


I am guessing a) heat, due to the Second Law of Thermodynamics. However, I do not know how I can calculate this percentage quantitatively. I know that in the transition reaction (oxidative carboxylation), one molecule of carbon dioxide is lost for each pyruvate molecule to become acetyl-CoA.

3. From an energetic viewpoint, what do muscle cells in oxygen deprivation gain from the reduction of pyruvate?

a) ATP & lactate b) ATP and recycled NAD+ c) CO2 and lactate d) ATP, alcohol, and NAD+ e) ATP, lactate, and CO2


Originally, I said a) which was incorrect; the correct answer is b).

I understand the ATP part of the answer, but not the part how muscle cells in oxygen deprivation gain NAD+. I know that NADH is oxidised to NAD+ cyclically in anaerobic cellular respiration so that 2 ATP can be produced from glycolysis; how do the muscle cells gain NAD+ though?

4. In fermentation by yeast, the final energy rich organic molecule is:

a) pyruvate b) acetaldehyde c) alcohol d) carbon dioxide


Initially, I answered c) but a) was the correct choice. I do not understand why pyruvate is the final energy-rich organic molecule; I thought that in anaerobic cellular respiration, it was only a product in glycolysis as alcohol is the final product of fermentation.

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Post by stopherlogic » Sat Sep 27, 2008 3:54 pm

I will start you off with the first one:

I will not answer but give you a few questions which you may need to ask yourself

- One hydrogen ion provides the energy for how many hydrogen ions to be pumped across to the intermembrane space?

- How many hydrogen ions does ATP synthase utilise to produce one molecule of ATP?

Failing that there is always............. http://en.wikipedia.org/wiki/Oxidative_phosphorylation

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Post by MrMistery » Sun Sep 28, 2008 5:21 am

2. The answer is b) ATP. here's why. One molecule of glucose releases by oxidation 686 kcal. During cellular respiration, 38 molecules of ATP are generated per glucose molecule, which is 38*7.3kcal=277.4 kcal that is stored in ATP. Doing the math, that adds up to about 38% efficiency, the rest of which is converted to heat.

3. some reactions in glycolysis are said to "produce NADH".That basically means that the reactions are coupled with the reduction of NAD+ to NADH. If there is no NAD+ available, the reduction cannot take place, and because the two reactions are coupled glycolysis cannot continue. therefore, the NADH needs to be recycled back to NAD+ if glycolysis is to continue

4. If you ask me, your answer(C) was correct.
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Post by MisterATP » Sun Sep 28, 2008 7:19 am

Talking about question 4, pyruvate is the final energy - rich molecule because in the case of fermentation of the alcohol, latter is not used for extracting any energy. I don't know exactly what is the fate of alcohol, but I just remember that in the yeast it is transported out of the cell and in humans alcohol dehydrogenase convert it to the aldehyde. So alcohol is like a waste. Am I right, Andrew? ;)

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Post by MrMistery » Sun Sep 28, 2008 3:32 pm

Alcohol is a waster, but it is still a product of fermentation. Pyruvate is not even a product of fermentation....
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vertciel
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Re:

Post by vertciel » Sun Sep 28, 2008 6:40 pm

stopherlogic wrote:I will start you off with the first one:

I will not answer but give you a few questions which you may need to ask yourself

- One hydrogen ion provides the energy for how many hydrogen ions to be pumped across to the intermembrane space?

- How many hydrogen ions does ATP synthase utilise to produce one molecule of ATP?

Failing that there is always............. http://en.wikipedia.org/wiki/Oxidative_phosphorylation


Thank you very much to everyone who replied.

I just want to confirm that I have answered #1:

Since there are three protein complexes where hydrons can be pumped from the matrix into the intermembrane space, the oxidation of NADH would cause one electron to move down the electron transport chain. Consequently, as FADH2 becomes oxidised and O2 becomes reduced, this one electrion will allow three H+ ions to move across the pH gradient.

Since ATP synthase utilises one H+ to produce one molecule ATP, the three hydrons will result in the production of three ATP molecules, all due to NADH's efforts.

Am I fully right? Please let me know if I have missed anything.

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