Question

Which of the following is/are the connecting link between the urea cycle and TCA/Krebs cycle ?
I. Fumarate
II. Ornithine
III. Aspartate
IV. Citrulline

• A. I only
• B. I and II only
• C. I and III only
• D. I, II, III, IV

Answer 1

The correct option is C I and III only

The urea cycle is a cycle of biochemical reactions that produces urea from ammonia. This cycle occurs in ureotelic organisms.
TCA (Tricarboxylic acid) / Krebs cycle / Citric acid cycle is a series of chemical reactions in the cell that breaks down food molecules into carbon dioxide, water, and energy. In plants and animals (eukaryotes), these reactions take place in the matrix of the mitochondria of the cell as part of cellular respiration.
The urea cycle and the citric acid cycle are two different and independent cycles but they are linked by fumarate/fumaric acid and aspartate/aspartic acid.
- Aspartate which is obtained from the transamination of oxaloacetate in TCA cycle is part of urea cycle.
- The fumarate which is produced in the urea cycle is an intermediate in the TCA cycle.