Impermeability of Mitochondrial Inner Membrane: Role of Cardiolipin Explained

The mitochondrial inner membrane’s impermeability to most ions, electrons, and protons is crucial for maintaining the proton gradient during oxidative phosphorylation. This MCQ highlights cardiolipin as the key factor ensuring this selective barrier function.

Correct Answer

(1) Cardiolipin is the right choice. Cardiolipin, a unique diphosphatidylglycerol lipid enriched in the inner mitochondrial membrane (about 20% of its phospholipids), contributes to its tight packing and low permeability. This structure creates an effective barrier against ions, protons, and electrons, essential for ATP synthesis via chemiosmosis.

Option Breakdown

Cardiolipin (Correct)

Found primarily in the inner mitochondrial membrane, cardiolipin’s four acyl chains and conical shape promote tight lipid packing and interactions with membrane proteins. This enhances the membrane’s hydrophobic core, restricting passive diffusion of charged species like ions and protons.

Collagen (Incorrect)

Collagen is a fibrous structural protein dominant in extracellular matrices like skin and connective tissues, not in eukaryotic membranes. It plays no role in mitochondrial impermeability.

Chitin (Incorrect)

Chitin is a polysaccharide forming exoskeletons in fungi and arthropods, providing rigidity in cell walls. Absent in animal mitochondria, it has zero involvement in membrane permeability.

Cellulose (Incorrect)

Cellulose, a plant cell wall polysaccharide, offers mechanical support in vegetation. It does not occur in animal cells or mitochondria, thus irrelevant to ion impermeability.

Why Impermeability Matters

The inner membrane’s barrier, bolstered by cardiolipin, supports the electron transport chain by preventing proton leaks, driving ATP production. Disruptions, like cardiolipin defects in Barth syndrome, impair this function.