Question
In the citric acid cycle (Krebs cycle / Tricarboxylic acid cycle), which of the following enzymes produces NADH (Reduced Nicotinamide Adenine Dinucleotide)?
| A. |
Succinate thiokinase |
| B. |
Succinate dehydrogenase |
| C. |
Isocitrate dehydrogenase |
| D. |
Fumarase |
Show Answer
|
Correct Answer » C Explanation |
 |
The citric acid cycle (TCA cycle) occurs in the mitochondrial matrix and is a central metabolic pathway for the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.
One of the key functions of the cycle is the generation of reducing equivalents:
-
NADH
-
FADH₂
These molecules donate electrons to the electron transport chain (ETC) to produce ATP via oxidative phosphorylation.
Steps Producing NADH in the TCA Cycle
NADH is generated at three steps:
-
Isocitrate → α-Ketoglutarate
Enzyme: Isocitrate dehydrogenase -
α-Ketoglutarate → Succinyl-CoA
Enzyme: α-Ketoglutarate dehydrogenase -
Malate → Oxaloacetate
Enzyme: Malate dehydrogenase