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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.
In biology, translation is the process in living cells in which proteins are produced using RNA molecules as templates. The generated protein is a sequence of amino acids. This sequence is determined by the sequence of nucleotides in the RNA. The nucleotides are considered three at a time. Each such triple results in addition of one specific amino acid to the protein being generated. The matching from nucleotide triple to amino acid is called the genetic code. The translation is performed by a large complex of functional RNA and proteins called ribosomes. The entire process is called gene expression.
A point mutation is a genetic mutation where a single nucleotide base is changed, inserted or deleted from a DNA or RNA sequence of an organism's genome. Point mutations have a variety of effects on the downstream protein product—consequences that are moderately predictable based upon the specifics of the mutation. These consequences can range from no effect to deleterious effects, with regard to protein production, composition, and function.
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protein-coding genes and non-coding genes.
MT-ND4 is a gene of the mitochondrial genome coding for the NADH-ubiquinone oxidoreductase chain 4 (ND4) protein. The ND4 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is the largest of the five complexes of the electron transport chain. Variations in the MT-ND4 gene are associated with age-related macular degeneration (AMD), Leber's hereditary optic neuropathy (LHON), mesial temporal lobe epilepsy (MTLE) and cystic fibrosis.
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 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 invertebrate mitochondrial code is a genetic code used by the mitochondrial genome of invertebrates. Mitochondria contain their own DNA and reproduce independently from their host cell. Variation in translation of the mitochondrial genetic code occurs when DNA codons result in non-standard amino acids has been identified in invertebrates, most notably arthropods. This variation has been helpful as a tool to improve upon the phylogenetic tree of invertebrates, like flatworms.
The euplotid nuclear code is the genetic code used by Euplotidae. The euplotid code is a socalled "symmetrical code", which results from the symmetrical distribution of the codons. This symmetry allows for arythmic exploration of the codon distribution. In 2013, shCherbak and Makukov, reported that "the patterns are shown to match the criteria of an intelligent signal."
The candidate division SR1 and gracilibacteria code is used in two groups of uncultivated bacteria found in marine and fresh-water environments and in the intestines and oral cavities of mammals among others. The difference to the standard and the bacterial code is that UGA represents an additional glycine codon and does not code for termination. A survey of many genomes with the codon assignment software Codetta, analyzed through the GTDB taxonomy system shows that this genetic code is limited to the Patescibacteria order BD1-5, not what are now termed Gracilibacteria, and that the SR1 genome assembly GCA_000350285.1 for which the table 25 code was originally defined is actually using the Absconditibacterales genetic code and has the associated three special recoding tRNAs. Thus this code may now be better named the "BD1-5 code".
The ascidian mitochondrial code is a genetic code found in the mitochondria of Ascidia.
The chlorophycean mitochondrial code is a genetic code found in the mitochondria of Chlorophyceae.
The pachysolen tannophilus nuclear code is a genetic code found in the ascomycete fungus Pachysolen tannophilus.
The karyorelictid nuclear code is a genetic code used by the nuclear genome of the Karyorelictea ciliate Parduczia sp. This code, along with translation tables 28 and 31, is remarkable in that every one of the 64 possible codons can be a sense codon. Translation termination probably relies on context, specifically proximity to the poly(A) tail.
The Condylostoma nuclear code is a genetic code used by the nuclear genome of the heterotrich ciliate Condylostoma magnum. This code, along with translation tables 27 and 31, is remarkable in that every one of the 64 possible codons can be a sense codon. Experimental evidence suggests that translation termination relies on context, specifically proximity to the poly(A) tail. Near such a tail, PABP could help terminate the protein by recruiting eRF1 and eRF3 to prevent the cognate tRNA from binding.
The Mesodinium nuclear code is a genetic code used by the nuclear genome of the ciliates Mesodinium and Myrionecta.
The peritrich nuclear code is a genetic code used by the nuclear genome of the peritrich ciliates Vorticella and Opisthonecta.
References
This article incorporates text from the United States National Library of Medicine, which is in the public domain. [4]
- ↑ Hoffman DC, Anderson RC, DuBois ML, Prescott DM (1995). "Macronuclear gene-sized molecules of hypotrichs". Nucleic Acids Research. 23 (8): 1279–83. doi:10.1093/nar/23.8.1279. PMC 306850 . PMID 7753617.
- ↑ Schneider SU, Leible MB, Yang XP (1989). "Strong homology between the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase of two species of Acetabularia and the occurrence of unusual codon usage". Molecular & General Genetics. 218 (3): 445–52. doi:10.1007/bf00332408. PMID 2573818. S2CID 31247623.
- ↑ Schneider SU, de Groot EJ (1991). "Sequences of two rbcS cDNA clones of Batophora oerstedii: structural and evolutionary considerations". Current Genetics. 20 (1–2): 173–5. doi:10.1007/bf00312782. PMID 1934113. S2CID 13509708.
- ↑ 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 29 January 2016.
