Mitochondria have their own DNA and manufacture a small number of their own proteins. However, the majority of mitochondrial proteins are coded for by nuclear genes. These are synthesized on free ribosomes and only imported into the mitochondrion posttrans-lationally. For example, proteins destined for the mitochondrial matrix carry a targeting sequence at their N terminus and are recognized by a receptor protein in the outer membrane. The mitochondrial receptor makes contact with a translocation complex, which unfolds the protein and moves it across both outer and inner membrane simultaneously. Once the protein is translocated, the targeting sequence is cleaved off and the protein refolded.
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