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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, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein.
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.
The central dogma of molecular biology deals with the flow of genetic information within a biological system. It is often stated as "DNA makes RNA, and RNA makes protein", although this is not its original meaning. It was first stated by Francis Crick in 1957, then published in 1958:
The Central Dogma. This states that once "information" has passed into protein it cannot get out again. In more detail, the transfer of information from nucleic acid to nucleic acid, or from nucleic acid to protein may be possible, but transfer from protein to protein, or from protein to nucleic acid is impossible. Information here means the precise determination of sequence, either of bases in the nucleic acid or of amino acid residues in the protein.
Virus classification is the process of naming viruses and placing them into a taxonomic system similar to the classification systems used for cellular organisms.
Codon usage bias refers to differences in the frequency of occurrence of synonymous codons in coding DNA. A codon is a series of three nucleotides that encodes a specific amino acid residue in a polypeptide chain or for the termination of translation.
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.
Transfer RNA is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length. In a cell, it provides the physical link between the genetic code in messenger RNA (mRNA) and the amino acid sequence of proteins, carrying the correct sequence of amino acids to be combined by the protein-synthesizing machinery, the ribosome. Each three-nucleotide codon in mRNA is complemented by a three-nucleotide anticodon in tRNA. As such, tRNAs are a necessary component of translation, the biological synthesis of new proteins in accordance with the genetic code.
An aminoacyl-tRNA synthetase, also called tRNA-ligase, is an enzyme that attaches the appropriate amino acid onto its corresponding tRNA. It does so by catalyzing the transesterification of a specific cognate amino acid or its precursor to one of all its compatible cognate tRNAs to form an aminoacyl-tRNA. In humans, the 20 different types of aa-tRNA are made by the 20 different aminoacyl-tRNA synthetases, one for each amino acid of the genetic code.
Xenobiology (XB) is a subfield of synthetic biology, the study of synthesizing and manipulating biological devices and systems. The name "xenobiology" derives from the Greek word xenos, which means "stranger, alien". Xenobiology is a form of biology that is not (yet) familiar to science and is not found in nature. In practice, it describes novel biological systems and biochemistries that differ from the canonical DNA–RNA-20 amino acid system. For example, instead of DNA or RNA, XB explores nucleic acid analogues, termed xeno nucleic acid (XNA) as information carriers. It also focuses on an expanded genetic code and the incorporation of non-proteinogenic amino acids, or “xeno amino acids” into proteins.
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.
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.
An expanded genetic code is an artificially modified genetic code in which one or more specific codons have been re-allocated to encode an amino acid that is not among the 22 common naturally-encoded proteinogenic amino acids.
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 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.
Parduczia is a genus of karyorelict ciliates in the family Geleiidae.
The Enterosoma genetic code translates AGG to methionine, as determined by the codon assignment software Codetta; it was further shown that this recoding is associated with a special tRNA with the appropriate anticodon and tRNA identity elements. The code is found in a small clade of species within the Enterosoma genus, according to the GTDB taxonomy system release 220. Codetta called the Enterosoma code for the following genome assemblies: GCA_002431755.1, GCA_002439645.1, GCA_002436825.1, GCA_002451385.1, GCA_002297105.1, GCA_002297045.1, GCA_002404995.1, and GCA_900549915.1.
The Absconditabacterales genetic code translates UGA to glycine, and CGG and GCA to tryptophan, as determined by the codon assignment software Codetta; it was further shown that these recodings are associated with three special tRNAs with appropriate anticodons and tRNA identity elements. Codetta called the Absconditibacterales code for the following genome assemblies: GCA_002792495.1, GCA_001007975.1, GCA_003488625.1, GCA_003260355.1, GCA_003242865.1, GCA_000350285.1, GCA_002746475.1, GCA_007116275.1, GCA_007115995.1, GCA_002361595.1, GCA_000503875.1, GCA_003543185.1, GCA_002441085.1, and GCA_002791215.1. Review of the GTDB taxonomy system for the order Absconditabacterales left two questionable genome assemblies ; spot-checking these two genomes shows that they both have all three special tRNAs, suggesting that the code is universal across the order.
References
- ↑ Shulgina, Yekaterina; Eddy, Sean R. (9 November 2021). "A computational screen for alternative genetic codes in over 250,000 genomes". eLife. 10. doi: 10.7554/eLife.71402 . PMC 8629427 . PMID 34751130.
- ↑ Parks, Donovan H.; Chuvochina, Maria; Chaumeil, Pierre-Alain; Rinke, Christian; Mussig, Aaron J.; Hugenholtz, Philip (September 2020). "A complete domain-to-species taxonomy for Bacteria and Archaea". Nature Biotechnol. 38 (9): 1079–1086. doi:10.1038/s41587-020-0501-8. PMID 32341564.