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ribosomes of organelles


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Ribosomes of chloroplasts and mitochondria show a variety of sedimentation constants. Chloroplast ribosomes are 70S, mitochondrial ribosomes from plant cells are 78S, mitochondrial ribosomes from fungal cells are 73S, and mitochondrial ribosomes from mammalian cells are 60S. Both mitochondria and chloroplasts are believed to have arisen from free-living prokaryotes that fused with primitive nucleated cells. The fact that translation starts with N-formylmethionine on the ribosomes of both mitochondria and chloroplasts supports the theory of their endosymbiotic orgin. See initiator tRNA, serial symbiosis theory, 5S rRNA.

Sedimentation Characteristics of Prokaryotic and Eukaryotic Ribosomes

Ribosomal Source

Ribosome

Large Subunit

Small Subunit

RNAs of Large Subunit

RNAs of Small Subunit

Bacteria

70S

50S

30S

23S (2,904 nt)

16S (1,542 nt)

5S (120 nt)

Mammalian cells

80S

60S

40S

28S (4,718 nt)

18S (1,874 nt)

5.8S (160 nt)

5S (120 nt)

Subjects: Genetics and Genomics.


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