Question

why mitochondria and plastids have their own DNA and ribosomes?

Answer 1

Mitochondria and plastids are semi-autonomous as they are only partially dependent on the cell to replicate and grow as they have their own DNA. They have their own ribosomes to make proteins

Answer 2

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Ribosomes on RER, which give RER its rough appearance, specialize in the synthesis of proteins that possess a signal sequence that directs them specifically to the ER for processing. Proteins synthesized by the RER have specific final destinations, such as the cell membrane, cell exterior, or the ER itself.

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