A diagram showing mtDNA (circular) and mitochondrial ribosomes among other mitochondria structures
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Mitochondria contain around 1000 proteins in yeast and 1500 proteins in humans. However, only 8 and 13 proteins are encoded in mitochondrial DNA in yeast and humans respectively. Most mitochondrial proteins are synthesized via cytoplasmic ribosomes.[3] Proteins that are key components in the electron transport chain are translated in mitochondria.[4][5]
Structure
Mammalian mitoribosomes have small 28S and large 39S subunits, together forming a 55S mitoribosome.[6][7] Plant mitoribosomes have small 33S and large 50S subunits, together forming a 78S mitoribosome.[6][7]
Animal mitoribosomes only have two rRNAs, 12S (SSU) and 16S (LSU), both highly minimized compared to their larger homologues.[6] Most eukaryotoes use 5S mitoribosomal RNA, animals, fungi, alveolates and euglenozoans being the exceptions.[8] A variety of methods have evolved to fill in the gap left by a missing 5S, with animals co-opting a Mt-tRNA (Val in vertebrates).[6][9]
Comparison to Other Ribosomes
Like the mitochondria itself, mitochondrial ribosomes are descended from bacterial ribosomes. [1] However, there has been significant divergence between the two as mitochondria evolved, leading to differences in configuration and function. [1] In configuration, the mitoribosome includes additional proteins in both its large and small subunits.[1] In function, mitoribosomes are much more limited in the proteins they translate, only producing a few proteins used mostly in the mitochondrial membrane. [1] Below is a table showing some properties of different ribosomes:
The mitochondrial ribosomal protein nomenclature generally follows that of bacteria, with extra numbers used for mitochondrion-specific proteins. (For more information on the nomenclature, see Ribosomal protein § Table of ribosomal proteins.)
^ abSpremulli LL (2016-01-01). "The Protein Biosynthetic Machinery of Mitochondria". In Bradshaw RA, Stahl PD (eds.). Encyclopedia of Cell Biology. Waltham: Academic Press. pp. 545–554. doi:10.1016/b978-0-12-394447-4.10066-5. ISBN978-0-12-394796-3.
