Question

In mitochondria, the enzymes of the Krebs Cycle are located

• A. On the membrane cristae
• B. In the matrix
• C. In between the membranes
• D. Smooth inner membrane

Hint:

To remember mitochondrial compartmentalization: 1. Matrix: Krebs cycle enzymes (soluble). 2. Inner Membrane (Cristae): Electron Transport Chain complexes and ATP synthase (insoluble).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Mitochondria are double-membraned organelles responsible for generating ATP through cellular respiration.
The different stages of aerobic respiration—link reaction, Krebs cycle, and electron transport—are compartmentalized within different structural regions of the mitochondrion.

Step 2: Detailed Explanation:
Let us analyze the localization of respiratory components:
The Mitochondrial Matrix (B): This is the dense, gel-like fluid inside the inner mitochondrial membrane.
It contains ribosomes, mitochondrial DNA, and the soluble enzymes responsible for the Link reaction (Pyruvate dehydrogenase) and the Krebs cycle (Citric acid cycle).
These soluble enzymes (such as citrate synthase, isocitrate dehydrogenase, and malate dehydrogenase) require the aqueous environment of the matrix to interact with their substrates.
The Inner Membrane Cristae (A): The inner membrane contains folds (cristae) that house the protein complexes of the electron transport chain (Complexes I to IV) and the ATP synthase complex.
There is one exception: succinate dehydrogenase (the enzyme catalyzing the conversion of succinate to fumarate in the Krebs cycle) is bound directly to the inner membrane as Complex II.
However, the vast majority of the Krebs cycle enzymes are soluble and located within the matrix.

Step 3: Final Answer:
The enzymes of the Krebs cycle are located in the mitochondrial matrix, which corresponds to option (B).