The intermediates of the citric acid cycle are constantly being depleted because they are used to produce many of the amino acids needed to make proteins

Question

The enzyme pyruvate carboxylase converts pyruvate to oxaloacetate to replenish these intermediates. Bacteria, but not animal cells, have additional enzymes that can carry out the reaction acetyl CoA + isocitrate -> oxaloacetate + succinate. Which of the following compounds will not support the growth of animal cells when used as the major source of carbon in food, but will support the growth of nonphotosynthetic bacteria?
(a) pyruvate
(b) glucose
(c) fatty acids
(d) fructose

Answer 1

(c) In oxidative metabolism, fatty acids can only be converted to acetyl CoA, which is completely oxidized to carbon dioxide through the citric acid cycle. In addition, bacteria can use some of this acetyl CoA as a source of carbon atoms to replenish the components of the citric acid cycle, whereas animals cannot.