© 2006 by Zack Smith. All rights reserved.
The Codons
All genes are composed of sequences of codons, which are triplets of nucleotide bases (A C G T/U). Ribosomes convert these sequences into proteins, which are polymers of amino acids.
Of the 64 possible codons, there are 20 amino acids coded for, 3 stop codons, and 1 start codon (the amino acid methionine). There are many redundant codons, which is important for protecting against transcription errors and mutations.
The Universal Codon of Life
| First Base | Second Base | Third Base | |||
|---|---|---|---|---|---|
| U | C | A | G | ||
| U | UUU = phenylalanine | UCU = serine | UAU = tyrosine | UGU = cysteine | U |
| UUC = phenylalanine | UCC = serine | UAC = tyrosine | UGC = cysteine | C | |
| UUA = leucine | UCA = serine | UAA = stop | UGA = stop | A | |
| UUG = leucine | UCG = serine | UAG = stop | UGG = tryptophan | G | |
| C | CUU = leucine | CCU = proline | CAU = histidine | CGU = arginine | U |
| CUC = leucine | CCC = proline | CAC = histidine | CGC = arginine | C | |
| CUA = leucine | CCA = proline | CAA = glutamine | CGA = arginine | A | |
| CUG = leucine | CCG = proline | CAG = glutamine | CGG = arginine | G | |
| A | AUU = isoleucine | ACU = threonine | AAU = asparagine | AGU = serine | U |
| AUC = isoleucine | ACC = threonine | AAC = asparagine | AGC = serine | C | |
| AUA = isoleucine | ACA = threonine | AAA = lysine | AGA = arginine | A | |
| AUG = methionine | ACG = threonine | AAG = lysine | AGG = arginine | G | |
| G | GUU = valine | GCU = alanine | GAU = aspartate | GGU = glycine | U |
| GUC = valine | GCC = alanine | GAC = aspartate | GGC = glycine | C | |
| GUA = valine | GCA = alanine | GAA = glutamate | GGA = glycine | A | |
| GUG = valine | GCG = alanine | GAG = glutamate | GGG = glycine | G |
Start & Stop codons
There is only one start codon, which is AUG. This is also the methionine amino acid.
There are three stop codons: UAA, UGA, UAG.