The Biology Project: Biochemistry

Metabolism Problem Set

Problem 7: Pyruvate/ Lactate Ratio

Explain why in anaerobic cells the ratio of pyruvate/ lactate is much less than 1 while under aerobic conditions the ratio of pyruvate/ lactate is much greater than 1.

A. Lactate is produced from pyruvate only under anaerobic conditions.
The glycolytic pathway produces pyruvate, which in the presence of oxygen will be further metabolized in the citric acid cycle to produce NADH and FADH2 for oxidative phosphorylation in the mitochondria. Normally, lactic acid will be low under these conditions. In the absence of oxygen (anaerobic), pyruvate must be converted to lactic acid, the only reaction that can regenerate NAD+ allowing further glycolysis. The production of lactic acid only under anaerobic conditions explains why pyruvate/lactate is much less than 1 in anaerobic cells and much greater than one in aerobic cells.

B. Under anaerobic conditions pyruvate is converted to carbon dioxide.

C. In anaerobic conditions, pyruvate is converted to glucose using the energy of light.

D. Lactate is the terminal electron acceptor under aerobic conditions.

E. Pyruvate is transported into mitochondria under anaerobic conditions.

The Biology Project
University of Arizona
Tuesday, August 20, 1996
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