Mitochondria protein synthesis dependence

Mitochondria can have different shapes, depending on the kind of cell they are in. The number of mitochondria present in a cell also varies with cell type and may range from a single large mitochondrion to thousands. The region inside the inner membrane is called the matrix. This is where the Krebs cycle that converts pyruvate into C02 and energy takes place, so it contains a lot of enzymes. Mitochondria contain ribosomes, small particles composed of RNA and protein that are the sites of protein synthesis. Mitochondria also contain their own special DNA. 

As far as Is known, all RNA transcripts of mtDNA and their translation products remain In the mitochondrion, and all mtDNA-encoded proteins are synthesized on mitochondrial ribosomes. Mitochondria encode the rRNAs that form mitochondrial ribosomes, although all but one or two of the rl-bosomal proteins (depending on the species) are imported from the cytosol. In most eukaryotes, all the tRNAs used for protein synthesis in mitochondria are encoded by mtDNAs. However, In wheat, in the parasitic protozoan Trypanosoma brucei (the cause of African sleeping sickness), and in ciliated... 

The oxidative phosphorylation system contains over 80 polypeptides. Only 13 of them are encoded by mtDNA, which is contained within mitochondria, and all the other proteins that reside in the mitochondrion are nuclear gene products. Mitochondria depend on nuclear genes for the synthesis and assembly of the enzymes for mtDNA replication, transcription, translation, and repair (Tl). The proteins involved in heme synthesis, substrate oxidation by TCA cycle, degradation of fatty acids by /i-oxidalion, part of the urea cycle, and regulation of apoptosis that occurs in mitochondria are all made by the genes in nuclear DNA. 

The oxidation reactions involved are catalyzed by a series of nicotinamide adenine dinucleotide (NAD+) or flavin adenine dinucleotide (FAD) dependent dehydrogenases in the highly conserved metabolic pathways of glycolysis, fatty acid oxidation and the tricarboxylic acid cycle, the latter two of which are localized to the mitochondrion, as is the bulk of coupled ATP synthesis. Reoxidation of the reduced cofactors (NADH and FADH2) requires molecular oxygen and is carried out by protein complexes integral to the inner mitochondrial membrane, collectively known as the respiratory, electron transport, or cytochrome, chain. Ubiquinone (UQ), and the small soluble protein cytochrome c, act as carriers of electrons between the complexes (Fig. 13.1.1). 

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