Question

Pyruvate is the end-product of glycolysis. Many organisms, such as anaerobic bacteria, can only produce energy by glycolysis; therefore, pyruvate has no more potential for ATP generation for these organisms. Rather than simply excrete pyruvate, this molecule is changed to another molecule such as lactate. In these organisms, why is pyruvate changed to lactate and excreted, rather than simply excreted?

A) Pyruvate export requires more energy than lactate.
B) Electrons (and protons) are added to pyruvate to make lactate.
C) NAD+ is regenerated as pyruvate is changed to lactate.
D) Substrate level phosphorylation changes pyruvate to lactate.
E) both choices B and C

Answer 1

Pyruvate is converted to lactate in anaerobic organisms to regenerate NAD+ which is necessary for glycolysis to continue, allowing the organisms to keep producing ATP. Thus, the correct answer is E) both choices B and C.

Step-by-step explanation:

Pyruvate is changed to lactate in anaerobic organisms to regenerate NAD+ which is necessary for glycolysis to continue producing ATP. When oxygen is low or absent, such as in anaerobic bacteria, the cell cannot proceed to aerobic respiration to make more ATP. Thus, the conversion of pyruvate to lactate allows the cell to sustain a limited production of ATP. If lactate were not formed, NADH would accumulate and the NAD+ pool would be depleted, halting glycolysis. This is crucial because glycolysis is an anaerobic process that produces a net gain of two ATP molecules, and in the absence of oxygen, it's the only energy-yielding pathway available to these organisms.

Therefore, the correct answer, considering the choices provided, is E) both choices B and C. This is because electrons (and protons) are indeed added to pyruvate to make lactate, and NAD+ is regenerated when pyruvate is reduced to lactate.