The mitochondrion is an organelle in a eukaryotic cell in which the electron transport chain takes place. The actual number of mitochondria per cell can be determined by electron microscopy. The most interesting aspect of the mitochondrion is that it has its own DNA. Mitochondria provide higher animals and plants with life sustaining cellular energy through the oxidative processes of the citric acid and fatty acid cycles.Animal mitochondrial DNA is extremely compact, with very few non coding regions and no introns. Each strand of duplex is transcribed into a single RNA product that is then cut into smaller pieces primarily by freeing the twenty two transfer RNAs interspersed throughout the genome.
Also formed are a 16S and a 12S ribosomal RNA. Although proteins and small molecules such as A TP and tRNAs can move in and out of the mitochondrion, large RNAs cannot. Most interestingly, all mtDNAs exhibit the same basic organization of genetic information. Each contains 2 rRNA genes, 22 tRNA genes, and 13 putative protein structural genes. Five genes encode known proteins but the products and functions of the other putative genes have not yet been identified. The entire mammalian mitochondrial genome is transcribed as one unit from a single promoter site and the giant primary transcript is then cleaved endonucleolytically to produce the individual tRNA, rRNA and mRNA molecule. Thus, the entire mtDNA is, in effect, equivalent to one operon in bacteria
The human mitochondrion has 13 genes. But some proteins are transported into the mitochondrion as they are synthesized in the cytoplasm under the control of nuclear genes. Proteins targeting the entry into the mitochondrion have a signal peptide of 85 amino acids in length. These transit peptides are usually cleaved off the precursor polypeptides during their transport across the mitochondrial membrane. In mammalian mitochondrial genes, there are no introns.
Some genes actually overlap and almost every single base pair can be assigned to a gene, with the exception of the D- Loop, a region concerned with the initiation of DNA replication. In yeast cells, 10-20 percent of the cellular DNA is localized in a single mitochondrion. Yeast mitochondria have introns and are not economical like that of mammalian mitochondria. Some suggest that the genes with introns have been originated in the nucleus and are later captured or integrated by the mitochondria. Even the genome size is five times bigger than mammalian mtDNA.
Also formed are a 16S and a 12S ribosomal RNA. Although proteins and small molecules such as A TP and tRNAs can move in and out of the mitochondrion, large RNAs cannot. Most interestingly, all mtDNAs exhibit the same basic organization of genetic information. Each contains 2 rRNA genes, 22 tRNA genes, and 13 putative protein structural genes. Five genes encode known proteins but the products and functions of the other putative genes have not yet been identified. The entire mammalian mitochondrial genome is transcribed as one unit from a single promoter site and the giant primary transcript is then cleaved endonucleolytically to produce the individual tRNA, rRNA and mRNA molecule. Thus, the entire mtDNA is, in effect, equivalent to one operon in bacteria
The human mitochondrion has 13 genes. But some proteins are transported into the mitochondrion as they are synthesized in the cytoplasm under the control of nuclear genes. Proteins targeting the entry into the mitochondrion have a signal peptide of 85 amino acids in length. These transit peptides are usually cleaved off the precursor polypeptides during their transport across the mitochondrial membrane. In mammalian mitochondrial genes, there are no introns.
Some genes actually overlap and almost every single base pair can be assigned to a gene, with the exception of the D- Loop, a region concerned with the initiation of DNA replication. In yeast cells, 10-20 percent of the cellular DNA is localized in a single mitochondrion. Yeast mitochondria have introns and are not economical like that of mammalian mitochondria. Some suggest that the genes with introns have been originated in the nucleus and are later captured or integrated by the mitochondria. Even the genome size is five times bigger than mammalian mtDNA.
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