Given below are statements on the citric acid cycle and urea cycle, which have shared metabolic intermediates.
A. Oxaloacetate is converted to aspartate.
B. Fumarate is a citric acid cycle intermediate.
C. Argininosuccinate is cleaved to fumarate and arginine.
D. Aspartate combines with citrulline to produce argininosuccinate in the mitochondrial matrix.
Which one of the following options represents the combination of all correct statements?

Correct option is D

Correct Answer
(d) A, B and C
Explanation
Oxaloacetate undergoes transamination to form aspartate, linking the TCA cycle to the urea cycle. Fumarate is a key intermediate of the citric acid cycle and is also generated during the urea cycle. Argininosuccinate is cleaved into arginine and fumarate, confirming statements A, B, and C as correct.
Information Booster
• The urea cycle and TCA cycle are interconnected through the aspartate–argininosuccinate shunt
• Fumarate formed in the urea cycle is converted to malate and reused in the TCA cycle
• Aspartate provides one nitrogen atom for urea synthesis
• This metabolic integration improves energy efficiency during nitrogen disposal
Additional Knowledge
Statement D is incorrect because the reaction between citrulline and aspartate occurs in the cytosol, not in the mitochondrial matrix. Only carbamoyl phosphate synthesis and citrulline formation take place in mitochondria, while argininosuccinate formation is a cytosolic step.