Question

SID: 5. (a) NADH is a very important fuel that is generated in part through alycolysis. After its synthesis, what is the path taken by NADH to "fuel" the cell? A paragraph should be sufficient to answer this question (b) NADH is very stable in the presence of oxygen. If NADH did react with oxygen, what would be the products of that reaction? [20 points]
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Answer 1

Answer 5a. NADH is a very important fuel that is generated in part through glycolysis. After its synthesis, the path taken by NADH to fuel the cell is as follows:

Now let us first consider how does the NADH is formed during cellular respiration. Two molecules of NADH is formed from NAD+in glycolysis from dehydrogenation of glyceraldehyde 3-pohosphate catalyzed by enzyme glyceraldehyde 3-pohosphate dehydrogenase. Then 2 molecule of NADH is formed from oxidative decarboxylation of pyruvate catalyzed by enzyme pyruvate dehydrogenase and product formed is acetyl CoA which then enter into TCA cycle. Six molecule of NADH is formed in TCA cycle at three different step. Thus total ten molecule of NADH is formed during different stages of cellular respiration.

NADH so formed (as above) then enter into electron transport chain which takes place in the mitochondria of cell through diiferent electron carrier such as ubiquinone, cytochrome b, c, a & a3 and then finally molecular oxygen. The electron from NADH then flows through these different electron carrier (arranged on the basis of their reduction potential in a series) to molecular oxygen which accept the electron finally and then molecular oxygen is reduced to water i.e. the final product of cellular respiration. During this electron transfer via electron transport chain, proton gradient is generated due to downhill movement of electron due to which there is release of energy which is conserved in the form of proton gradient across mitochondrial inner membrane and matrix. This proton gradient is then utilized for the synthesis of ATP (i.e. energy currency of cell that fuel the cell for various cellular processes) from ADP and Pi through coupled process explained by chemiosmotic coupling theory propsed by P. Mitchell. In this way 2.5 -3 molecule of ATP is generated from one molecule of NADH due to 2.5 -3 energy conserving step during electron transport chain.

Answer 5b. NADH is very stable in the presence of oxygen. If NADH did react with the oxygen, then the product of that reaction would be NAD+ and water. The reaction is shown as follows:

4 NADH + O2 $\rightarrow$ 4 NAD+ + 2 H2O