Question

How many times dehydrogenation occurs during Krebs cycle?

• A. One
• B. Two
• C. Three
• D. Four

Hint:

Count the oxidation steps in which hydrogen is removed from a substrate in one turn of the cycle.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept
In the Krebs cycle, dehydrogenation means removal of hydrogen atoms, which are picked up by \(\text{NAD}^{+}\) or FAD.

Step 2: List the steps
Isocitrate is converted to \(\alpha\)-ketoglutarate by isocitrate dehydrogenase.
\(\alpha\)-Ketoglutarate is converted to succinyl-CoA.
Succinate is converted to fumarate.
Malate is converted to oxaloacetate.

Step 3: Count
That gives four dehydrogenation steps in one turn of the cycle.

Final Answer:
Dehydrogenation occurs four times in the Krebs cycle. \[ \boxed{\text{(D) }\text{Four}} \]