Mitochondria-Capaldi-9 - different from the cytosolic ribosomes that convert the nuclear genes to proteins The DNA strands in mitochondria are not

Mitochondria-Capaldi-9 - different from the cytosolic...

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different from the cytosolic ribosomes that convert the nuclear genes to proteins. The DNA strands in mitochondria are not well protected e.g. by chromatin as in the nucleus, but instead are bundled with several DNA-binding proteins into so-called nucleoids. These nucleoids are irregular ellipsoidal in shape and typically contain a single copy of mtDNA encased in the mitochondrial transcription factor TFAM. The average nucleoid diameter is around 220 nm in HepG2 cells. On fragmentation of the mitochondrial reticulum there is one nucleoid per minimal sized fragment. The crystal structure of TFAM shows that it bends mtDNA in a sharp U-turn. Several other proteins are a part, often transiently, of the nucleoid including prohibitin, single-stranded DNA-binding protein, mtSSB,, twinkle, pol G, ATAD3 and Lon. There is very limited repair of mtDNA with the result that mutations readily accumulate. Of considerable importance, unlike the nuclear genome which consists of a paternal and a maternal copy of each,

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