Question

1. At what stages do the catabolic products of lipids and proteins enter the glycolysis and citric acid cycle?

Answer 1

Lysis of lipids mainly produces glycerol (enters glycolysis after transformation to D-Glyceraldehyde 3-phosphate) and fatty acids (enter Krebs cycle after breakdown to acetyl-CoA and, in case of odd-number fatty acids, succinyl-CoA). Also, ω-oxidation of fatty acids produces succinate, which can enter citric acid cycle.

Catabolic metabolism of amino acids results in production of oxaloacetate, malate (in urea cycle), fumarate, succinyl-CoA, acetyl-CoA (directly or through pyruvate) and α-ketoglutarate, all of which enter citric acid cycle.