Codon
A codon is a triplet of Nucléotide S has, C, U or G of ARN messenger (ARNm).
In Combinative term of , an assembly of 3 elements, taken each one among 4 possible, led to 64 possibilities (64 different codes ).
Each possible code can indicate an Amino-acid (for a total of 20 current amino-acids, plus the Sélénocystéine). Several codes can indicate the even amino-acid. Let us code UAG, UGA and UAA do not indicate any amino-acid in general; it is code them stop (exceptionally, codon UGA sometimes also codes for a Sélénocystéine, essential to the function of the Sélénoprotéine S). When a Ribosome receives one of the latter during the complex process which form the Synthèse of the proteins, it stops coding the gene in progress.
One distinguishes also the code from the beginning of reading: AUG (methionine). At the Procaryotic S, sometimes this codon is GUG or UUG (for example, at E. coli 77% of the coding sequences starts with AUG, 14% by GUG and 8% by UUG). In general, any protein will start with a methionine (at the procaryotes, AUG will code for a NR - formyl-methionine (fMet) if it is the first codon, and for an ordinary methionine if it is a codon being elsewhere within the framework of reading).
These codes are described in the article “genetic Code”.
See too
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