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Kreb's Cycle and Energy

1. Since lactate is a "dead end" product of metabolism in the sense that its sole fate is to be converted into pyruvate, what is the purpose of its formation?

2. The molecule 2, 4 -dinitrophenol (DNP) is an uncoupler of oxidative phosphorylation. For a short period of time, it was prescribed clinically as a pill for weight reduction (against the advice of ssientists). Explain the basis for its ability to cause weight loss.

3. Consider the following reactions, which are two consecutive steps in the cyclic, multistep metabolic pathway referred to as the Kreb's cycle. The first reaction, which is not thermodynamically spontaneous, immediately precedes the second reaction, which occurs spontaneously. The two reactions are catalyzed by two independent enzymes.

L-malate + NAD plus<----> oxaloacetate + NADH + H plus +7(delta G knot --KJ/mol)
Acetyl - CoA + oxaloacetate <----------> citrate +CoA -8( " " " " " )

How can the initial reaction occur in this pathway with such a high positive standard free energy?

Solution Preview

1. Under conditions of low oxygen, when there isn't enough molecular oxygen to act as the final electron acceptor in oxidative phosphorylation, the electron transport system backs up. As a result, the reduced cofactors like NADH and FADH2 are not oxidized back to NAD+ and FAD. As a result of not having enough oxidized cofactors, the Kreb's cycle and glycolysis shuts down; however, glycolysis can continue to occur IF some of the NADH can be reoxidized back to NAD+. Thus, the purpose of the conversion of pyruvate to lactate is to oxidize NADH to NAD+. This little bit of NAD+ can be used in glycolysis to keep it going. That converts glucose to pyruvate, and then ...

Solution Summary

This solution is provided in 452 words. It discusses the Kreb's cycle and how this relates to the creation of pyruvate, and Le Chatelier's principle is used to relate to forces of equilibrium.