Question

In Krebs' cycle, GTP is produced during the conversion of ___.

• A. \(\alpha\)-ketoglutarate to succinyl CoA.
• B. fumarate to malate.
• C. succinate to fumarate.
• D. succinyl CoA to succinic acid.

Hint:

GTP is made by substrate-level phosphorylation when succinyl CoA becomes succinic acid.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept
The only substrate-level phosphorylation in the Krebs cycle takes place at the succinyl CoA step.

Step 2: The step
Succinyl CoA is split into succinic acid and CoA by succinyl-CoA synthetase.
The energy of the thioester bond is used to make GTP from GDP and inorganic phosphate.

Step 3: Other steps
\(\alpha\)-Ketoglutarate to succinyl CoA gives NADH and \(\text{CO}_{2}\). Succinate to fumarate gives \(\text{FADH}_{2}\). Fumarate to malate is only hydration.

Final Answer:
GTP is formed when succinyl CoA is converted to succinic acid. \[ \boxed{\text{(D) }\text{succinyl CoA to succinic acid.}} \]