Mitochondrial ribosome
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Through Translation (biology), Human and Electron transport chain
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. Proteins that are key components in the electron transport chain are translated in mitochondria.
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Structure
Mammalian mitoribosomes have small 28S and large 39S subunits, together forming a 55S mitoribosome. Plant mitoribosomes have small 33S and large 50S subunits, together forming a 78S mitoribosome.
Animal mitoribosomes only have two rRNAs, 12S (SSU) and 16S (LSU), both highly minimized compared to their larger homologues. Most eukaryotoes use 5S mitoribosomal RNA, animals, fungi, alveolates and euglenozoans being the exceptions. 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).
Comparison to other ribosomes
Like mitochondria itself is descended from bacteria, mitochondrial ribosomes are descended from bacterial ribosomes. As mitochondria evolved however, the mitoribosome has significantly diverged from its bacterial cousins leading to differences in configuration and function. In configuration, the mitoribosome includes additional proteins in both its large and small subunits. In function, mitoribosomes are much more limited in the proteins they translate, only producing a few proteins, used mostly in the mitochondrial membrane. Below is a table showing some properties of different ribosomes:
Diseases
As the mitoribosome is responsible for the manufacture of proteins necessary for the electron transport chain, malfunctions in the mitoribosome can result in metabolic disease. In humans, disease particularly manifests in energy-reliant organs such as the heart, brain, and muscle. Disease either originates from mutations in mitochondrial rRNA or genes encoding the mitoribosomal proteins. In the case of mitoribosomal protein mutation, heredity of disease follows Mendelian inheritance as these proteins are encoded in the nucleus. On the other hand, because mitochondrial rRNA is encoded in the mitochondria, mutations in rRNA are maternally inherited. Examples of diseases in humans caused by these mutations include Leigh syndrome, deafness, neurological disorders, and various cardiomyopathies. In plants, mutation in mitoribosomal proteins can result in stunted size and distorted leaf growth.
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.)
- MRPS1, MRPS2, MRPS3, MRPS4, MRPS5, MRPS6, MRPS7, MRPS8, MRPS9, MRPS10, MRPS11, MRPS12, MRPS13, MRPS14, MRPS15, MRPS16, MRPS17, MRPS18, MRPS19, MRPS20, MRPS21, MRPS22, MRPS23, MRPS24, MRPS25, MRPS26, MRPS27, MRPS28, MRPS29, MRPS30, MRPS31, MRPS32, MRPS33, MRPS34, MRPS35
- MRPL1, MRPL2, MRPL3, MRPL4, MRPL5, MRPL6, MRPL7, MRPL8, MRPL9, MRPL10, MRPL11, MRPL12, MRPL13, MRPL14, MRPL15, MRPL16, MRPL17, MRPL18, MRPL19, MRPL20, MRPL21, MRPL22, MRPL23, MRPL24, MRPL25, MRPL26, MRPL27, MRPL28, MRPL29, MRPL30, MRPL31, MRPL32, MRPL33, MRPL34, MRPL35, MRPL36, MRPL37, MRPL38, MRPL39, MRPL40, MRPL41, MRPL42
- rRNA: MT-RNR1, MT-RNR2, MT-TV (mitochondrial)