Genetic Code
The genetic code is the set of rules by which information encoded within mRNA sequences is converted into amino acid sequences (polypeptides) by living cells
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The genetic code is represented by a table that identifies the corresponding amino acid for each codon combination
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As there are four possible bases in a nucleotide sequence, and three bases per codon, there are 64 codon possibilities (43)
Occasionally, the genetic code may occasionally be represented according to the sense strand of DNA (non-coding strand)
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These sequences are identical to the mRNA codons with the exception of thymine (T) being present instead of uracil (U)
Genetic Code
There are two key features of the genetic code: it is universal and it has degeneracy (also referred to as redundancy)
Universal
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The genetic code is universal as almost every living organism uses the same code (there are a few rare and minor exceptions)
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As the same codons code for the same amino acids in all living things, genetic information is potentially transferrable between species
Degeneracy
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As the genetic code has only ~20 amino acids but 64 different codon combinations, more than one codon may code for a single amino acid
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Degeneracy always occurs in the third base of a codon (the wobble position), as the third base of an anticodon is not orientated optimally for base pairing
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Degeneracy of the genetic code allows for the occurrence of silent mutations – whereby a change in the DNA sequence does not alter the polypeptide sequence
