How does mitochondria differ in transcription and translation compared to the nucleus?

• A. Mitochondria have their own genome and ribosomes (55S) and transcription/translation machinery more similar to bacteria.
• B. Mitochondria use host cell transcription only; no translation occurs there.
• C. Mitochondria share identical transcription machinery with nuclear genome.
• D. Mitochondria only transcribe but do not translate.

Answer: (A)

Mitochondria have their own genome and their own protein-synthesis machinery, which comes from bacteria. Their DNA is circular and carries a small set of genes, while most mitochondrial proteins are encoded in the nucleus and imported into the organelle. Transcription inside mitochondria uses a mitochondrial RNA polymerase that is more like bacterial enzymes than the nuclear eukaryotic ones. Translation happens on mitochondrial ribosomes, which are 55S and resemble bacterial ribosomes more than the 80S ribosomes used in the cytosol. Because of this endosymbiotic heritage, mitochondria can transcribe and translate some of their own genes independently, whereas the nucleus relies on the host cell’s eukaryotic transcription and translation machinery for most proteins. The result is a clear difference: mitochondria maintain their own genome and bacterial-like transcription/translation system, while the nucleus uses its own eukaryotic machinery for most gene expression. Translation does occur in mitochondria, so statements that say no translation happens there aren’t accurate, and mitochondrial machinery is not identical to nuclear machinery.