Q.Why do we believe chloroplast and mitochondria to be semi-autonomous organelle?
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Start your 14-day free trial to unlock the full solution →Chloroplasts and mitochondria are semi-autonomous because each carries its own circular DNA and 70S ribosomes, letting it make some of its own proteins and divide somewhat independently — but each still depends on the nucleus for most of its proteins, so the independence is only partial.
Most organelles in a eukaryotic cell have no genetic material of their own and are entirely dependent on the nucleus for the information needed to build and maintain them. Chloroplasts and mitochondria are a striking exception. Each contains a small, circular, double-stranded DNA molecule that is 'naked' — not associated with histone proteins — closely resembling the circular DNA typical of bacteria, in contrast to the long, histone-wrapped chromosomes found in the nucleus.
Alongside this DNA, both organelles also possess their own ribosomes. These are smaller, 70S-type ribosomes, matching the ribosomes found in prokaryotic cells, rather than the larger 80S ribosomes that carry out protein synthesis elsewhere in the eukaryotic cell's cytoplasm. Using this DNA and these ribosomes, chloroplasts and mitochondria are able to transcribe and translate at least some of their own proteins, and they are capable of growing and dividing by a fission-like process that is not strictly tied to the timing of the rest of the cell's division cycle. …
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