Mitochondrial proteome — Which statement correctly describes the genetic origin and synthesis location of mitochondrial proteins in eukaryotic cells?

Introduction / Context:Mitochondria retain a small genome that encodes a subset of oxidative phosphorylation components and rRNAs/tRNAs. However, the majority of mitochondrial proteins are encoded in the nucleus, synthesized on cytosolic ribosomes, and imported via translocases. Understanding this division of genetic labor is essential in genetics, bioenergetics, and cell biology.

Given Data / Assumptions:

• Mitochondrial DNA encodes a limited number of polypeptides (e.g., parts of Complexes I, III, IV, V), rRNAs, and tRNAs.
• Nuclear DNA encodes hundreds of mitochondrial proteins (metabolism, import machinery, dynamics).
• Protein import depends on TOM/TIM complexes and targeting sequences.

Concept / Approach:Eliminate absolutes that contradict known division of labor. Neither “all mitochondrial proteins are encoded in mitochondria” nor “all are imported” is correct. The accurate statement is that some are mitochondrial-encoded, but most are nuclear-encoded and imported.

Step-by-Step Solution:

Verification / Alternative check:Mutations in nuclear genes for import machinery produce mitochondrial disease phenotypes, highlighting reliance on nuclear genome.

Why Other Options Are Wrong:

Common Pitfalls:Assuming organelles with their own DNA encode all of their proteins; in reality, most are nuclear-encoded.

Final Answer:Some mitochondrial proteins are encoded/synthesized in mitochondria, many others are nuclear-encoded and imported.