A diagram showing mtDNA (circular) and mitochondrial ribosomes among other mitochondria structures
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The mitochondrial ribosome, or mitoribosome, is a protein complex that is active in mitochondria and functions as a riboprotein for translating mitochondrial mRNAs encoded in mtDNA. Mitoribosomes, like cytoplasmicribosomes, consist of two subunits — large (mtLSU) and small (mt-SSU).[1] However, the ratio of rRNA/protein is different from cytoplasmic ribosomes. Mitoribosomes consist of several specific proteins and less rRNAs.[1]
Function
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.[2] Proteins that are key components in the electron transport chain are translated in mitochondria.[3][4]
Structure
Mammalian mitoribosomes have small 28S and large 39S subunits, together forming a 55S mitoribosome.[5][6] Plant mitoribosomes have small 33S and large 50S subunits, together forming a 78S mitoribosome.[5][6]
Animal mitoribosomes only have two rRNAs, 12S (SSU) and 16S (LSU), both highly minimizeed compared to their larger homologues.[5] Most eukaryotoes use 5S mitoribosomal RNA, animals, fungi, alveolates and euglenozoans being the exceptions.[7] 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).[5][8]
Genes
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.)
