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A typical operon. In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. [1] The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splicing to create monocistronic mRNAs that are translated separately, i.e. several strands of mRNA that each encode a single gene product.
For example, an operon is a stretch of DNA that is transcribed to create a contiguous segment of RNA, but contains more than one cistron / gene. The operon is said to be polycistronic, whereas ordinary genes are said to be monocistronic.
When translating from genome to protein, the use of the correct genetic code is essential. The mitochondrial codes are the relatively well-known examples of variation. The translation table list below follows the numbering and designation by NCBI. [ 2 ]
[20] [21] For example, in 1981, it was discovered that the use of codons AUA, UGA, AGA and AGG by the coding system in mammalian mitochondria differed from the universal code. [20] Stop codons can also be affected: in ciliated protozoa, the universal stop codons UAA and UAG code for glutamine. [21] [note 4] Four novel alternative genetic codes ...
A structural gene is a gene that codes for any RNA or protein product other than a regulatory factor (i.e. regulatory protein).A term derived from the lac operon, structural genes are typically viewed as those containing sequences of DNA corresponding to the amino acids of a protein that will be produced, as long as said protein does not function to regulate gene expression.
Gene structure is the organisation of specialised sequence elements within a gene. Genes contain most of the information necessary for living cells to survive and reproduce. [ 1 ] [ 2 ] In most organisms, genes are made of DNA, where the particular DNA sequence determines the function of the gene.
An mRNA molecule is said to be monocistronic when it contains the genetic information to translate only a single protein chain (polypeptide). This is the case for most of the eukaryotic mRNAs. [28] [29] On the other hand, polycistronic mRNA carries several open reading frames (ORFs), each of which is
In particular, the genetic code clusters certain amino acid assignments. Amino acids that share the same biosynthetic pathway tend to have the same first base in their codons. This could be an evolutionary relic of an early, simpler genetic code with fewer amino acids that later evolved to code a larger set of amino acids. [84]