Question

How many times does oxidation occur in the Krebs cycle of cellular respiration?

• A. Once
• B. Twice
• C. Three times
• D. Four times

Hint:

Each oxidation step in the Krebs cycle is coupled with the reduction of an electron carrier (NAD\(^+\) or FAD), which later donates electrons to the electron transport chain to generate ATP.

Answer 1

The Correct Option is D

Step 1: Overview of the Krebs cycle. The Krebs cycle, also known as the citric acid cycle, is a crucial metabolic pathway in cellular respiration. It takes place in the mitochondrial matrix and is responsible for oxidizing acetyl-CoA to carbon dioxide while reducing NAD\(^+\) and FAD to NADH and FADH\(_2\), which are used in the electron transport chain to generate ATP. 

Step 2: Oxidation events in the Krebs cycle. Oxidation occurs in the following steps of the Krebs cycle: 1. Isocitrate is oxidized to \(\alpha\)-ketoglutarate, reducing NAD\(^+\) to NADH. 2. \(\alpha\)-ketoglutarate is oxidized to succinyl-CoA, reducing NAD\(^+\) to NADH. 3. Succinate is oxidized to fumarate, reducing FAD to FADH\(_2\). 4. Malate is oxidized to oxaloacetate, reducing NAD\(^+\) to NADH. Hence, oxidation occurs four times in the Krebs cycle.