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The genetic code is the set of rules used by living cells to translate information encoded within genetic material into proteins. Translation is accomplished by the ribosome, which links proteinogenic amino acids in an order specified by messenger RNA (mRNA), using transfer RNA (tRNA) molecules to carry amino acids and to read the mRNA three nucleotides at a time. The genetic code is highly similar among all organisms and can be expressed in a simple table with 64 entries.
In molecular biology, a stop codon is a codon that signals the termination of the translation process of the current protein. Most codons in messenger RNA correspond to the addition of an amino acid to a growing polypeptide chain, which may ultimately become a protein; stop codons signal the termination of this process by binding release factors, which cause the ribosomal subunits to disassociate, releasing the amino acid chain.
Pyrrolysine is an α-amino acid that is used in the biosynthesis of proteins in some methanogenic archaea and bacteria; it is not present in humans. It contains an α-amino group, a carboxylic acid group. Its pyrroline side-chain is similar to that of lysine in being basic and positively charged at neutral pH.
In molecular biology and genetics, translation is the process in which ribosomes in the cytoplasm or endoplasmic reticulum synthesize proteins after the process of transcription of DNA to RNA in the cell's nucleus. The entire process is called gene expression.
The Nirenberg and Leder experiment was a scientific experiment performed in 1964 by Marshall W. Nirenberg and Philip Leder. The experiment elucidated the triplet nature of the genetic code and allowed the remaining ambiguous codons in the genetic code to be deciphered.
The start codon is the first codon of a messenger RNA (mRNA) transcript translated by a ribosome. The start codon always codes for methionine in eukaryotes and Archaea and a N-formylmethionine (fMet) in bacteria, mitochondria and plastids. The most common start codon is AUG.
A codon table can be used to translate a genetic code into a sequence of amino acids. The standard genetic code is traditionally represented as an RNA codon table, because when proteins are made in a cell by ribosomes, it is messenger RNA (mRNA) that directs protein synthesis. The mRNA sequence is determined by the sequence of genomic DNA. In this context, the standard genetic code is referred to as translation table 1. It can also be represented in a DNA codon table. The DNA codons in such tables occur on the sense DNA strand and are arranged in a 5′-to-3′ direction. Different tables with alternate codons are used depending on the source of the genetic code, such as from a cell nucleus, mitochondrion, plastid, or hydrogenosome.
The pterobranchia mitochondrial code is a genetic code used by the mitochondrial genome of Rhabdopleura compacta (Pterobranchia). The Pterobranchia are one of the two groups in the Hemichordata which together with the Echinodermata and Chordata form the three major lineages of deuterostomes. AUA translates to isoleucine in Rhabdopleura as it does in the Echinodermata and Enteropneusta while AUA encodes methionine in the Chordata. The assignment of AGG to lysine is not found elsewhere in deuterostome mitochondria but it occurs in some taxa of Arthropoda. This code shares with many other mitochondrial codes the reassignment of the UGA STOP to tryptophan, and AGG and AGA to an amino acid other than arginine. The initiation codons in Rhabdopleura compacta are ATG and GTG.
The vertebrate mitochondrial code is the genetic code found in the mitochondria of all vertebrata.
The yeast mitochondrial code is a genetic code used by the mitochondrial genome of yeasts, notably Saccharomyces cerevisiae, Candida glabrata, Hansenula saturnus, and Kluyveromyces thermotolerans.
The mold, protozoan, and coelenterate mitochondrial code and the mycoplasma/spiroplasma code is the genetic code used by various organisms, in some cases with slight variations, notably the use of UGA as a tryptophan codon rather than a stop codon.
The invertebrate mitochondrial code is a genetic code used by the mitochondrial genome of invertebrates.
The echinoderm and flatworm mitochondrial code is a genetic code used by the mitochondria of certain echinoderm and flatworm species.
The ascidian mitochondrial code is a genetic code found in the mitochondria of Ascidia.
The alternative flatworm mitochondrial code is a genetic code found in the mitochondria of Platyhelminthes and Nematodes.
The trematode mitochondrial code is a genetic code found in the mitochondria of Trematoda.
The Thraustochytrium mitochondrial code is a genetic code found in the mitochondria of the labyrinthulid protist Thraustochytrium aureum. The mitochondrial genome was sequenced by the Organelle Genome Megasequencing Program.
The pachysolen tannophilus nuclear code is a genetic code found in the ascomycete fungus Pachysolen tannophilus.
The Cephalodiscidae mitochondrial code is a genetic code used by the mitochondrial genome of Cephalodiscidae (Pterobranchia). The Pterobranchia are one of the two groups in the Hemichordata which together with the Echinodermata and Chordata form the major clades of deuterostomes.
Spizellomyces punctatus is a chytrid fungal species that is found in soil. It is a saprotrophic fungus that colonizes decaying plant material. Being an early diverging fungus, S. punctatus retains ancestral cellular features that are also found in animals and amoebae. Its pathogenic relatives, Batrachochytrium dendrobatidis and B. salamandrivorans, infect amphibians and cause global biodiversity loss. The pure culture of S. punctatus was first obtained by Koch.
References
This article incorporates text from the United States National Library of Medicine, which is in the public domain. [3]
- ↑ Y Hayashi-Ishimaru; T Ohama; Y Kawatsu; K Nakamura; S Osawa (June 1996). "UAG is a sense codon in several chlorophycean mitochondria". Current Genetics. 30 (1): 29–33. doi:10.1007/s002940050096. PMID 8662206. S2CID 7175211.
- ↑ M. J. Laforest; I. Roewer; B. F. Lang (1 February 1997). "Mitochondrial tRNAs in the lower fungus Spizellomyces punctatus: tRNA editing and UAG 'stop' codons recognized as leucine". Nucleic Acids Research. 25 (3): 626–32. doi:10.1093/nar/25.3.626. PMC 146481 . PMID 9016605.
- ↑ Elzanowski A, Ostell J, Leipe D, Soussov V. "The Genetic Codes". Taxonomy browser. National Center for Biotechnology Information (NCBI), U.S. National Library of Medicine. Retrieved 10 August 2016.