Question

What is the location of enzymes of electron transport chain in an animal cell?

• A. Plasma membrane
• B. Inner mitochondrial membrane
• C. Rough endoplasmic reticulum
• D. Mitochondrial matrix

Hint:

While the Krebs cycle enzymes are located in the soluble matrix of the mitochondria, the Electron Transport Chain enzymes are physically embedded in the inner membrane.
The only exception is Succinate Dehydrogenase (Complex II), which belongs to both pathways and is membrane-bound.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The Electron Transport Chain (ETC) is a series of protein complexes that transfer electrons from electron donors (NADH and $\text{FADH}_2$) to electron acceptors (molecular oxygen, $\text{O}_2$) via redox reactions.
This process is coupled with the pumping of protons across a membrane to establish a proton gradient used for ATP synthesis.

Step 2: Detailed Explanation:
In eukaryotic cells, the enzymes and cofactors of the electron transport chain are integrated directly into the inner mitochondrial membrane.
This membrane is folded into numerous invaginations called cristae, which vastly increase the surface area available to house these complexes:
- Complex I: NADH dehydrogenase
- Complex II: Succinate dehydrogenase
- Complex III: Cytochrome $bc_1$ complex
- Complex IV: Cytochrome $c$ oxidase
- Complex V: ATP synthase (though technically part of oxidative phosphorylation rather than the ETC itself)
The impermeable nature of the inner mitochondrial membrane is essential because it allows the establishment of a high concentration of protons in the intermembrane space, generating the proton-motive force required to drive ATP synthesis.
The mitochondrial matrix contains the soluble enzymes of the Krebs cycle and fatty acid oxidation, while the plasma membrane of eukaryotic cells does not contain the ETC (unlike prokaryotes, where the ETC is located in the plasma membrane).

Step 3: Final Answer:
Therefore, the enzymes of the electron transport chain are located in the inner mitochondrial membrane, corresponding to option (B).