Another Codon Wheel
The Genetic Code: The colour wheel reveals RNA triplet codes for various amino acids, the links in the chain of protein molecules. For examples, the chain CAG demands the attachment of a glutamic acid link (top left). Notice how the code is redundant for most amino acids, preventing some form of protection against mutations.
This picture is taken from P.W. Atkins Galileo's Finger and further adapted at The Ribosome: BSBX2 2009, Practical 7, Structural Bioinformatics:
"Which amino acid that is going to be incorporated into the growing peptide chain is determined by the codon (a triplet of bases) on the mRNA (fig 2). Many amino acids have several codon options, so each amino acid can be incorporated by a set of different codons. For example, the amino acid lysine has two codons and serine has 6 different codons. Codons for the same amino acid tend to have the same nucleotides for the two first positions and only differ in the third position. Only two amino acids, tryptophan and methionine, have one single codon. The codon for methionine is also a start signal for protein synthesis. There are also several stop codons, which are used as a signal when the protein message is ending. These are decoded not by a tRNA but by a protein called release factor."
"The reading of the mRNA codon is performed by the three bases on the tRNA that makes up the so called anti-codon. If the pairing is correct, this amino acid will be incorporated into the growing peptide chain. Since most amino acids have several codons at their disposal, this must mean that either there must be many more tRNAs than is absolutely necessary, or that some tRNAs can base pair with more than one codon. In fact, both scenarios are true. Some amino acids do have more than one tRNA but. Also, while the first two base pairs strictly have to be correctly base paired, in the third so-called wobble position of the codon, some mismatches and non-standard base pairs are tolerated. This also explains why often different codons for the same amino acid have the same bases in the first two positions."
Another Codon Wheel
The Genetic Code: The colour wheel reveals RNA triplet codes for various amino acids, the links in the chain of protein molecules. For examples, the chain CAG demands the attachment of a glutamic acid link (top left). Notice how the code is redundant for most amino acids, preventing some form of protection against mutations.
This picture is taken from P.W. Atkins Galileo's Finger and further adapted at The Ribosome: BSBX2 2009, Practical 7, Structural Bioinformatics:
"Which amino acid that is going to be incorporated into the growing peptide chain is determined by the codon (a triplet of bases) on the mRNA (fig 2). Many amino acids have several codon options, so each amino acid can be incorporated by a set of different codons. For example, the amino acid lysine has two codons and serine has 6 different codons. Codons for the same amino acid tend to have the same nucleotides for the two first positions and only differ in the third position. Only two amino acids, tryptophan and methionine, have one single codon. The codon for methionine is also a start signal for protein synthesis. There are also several stop codons, which are used as a signal when the protein message is ending. These are decoded not by a tRNA but by a protein called release factor."
"The reading of the mRNA codon is performed by the three bases on the tRNA that makes up the so called anti-codon. If the pairing is correct, this amino acid will be incorporated into the growing peptide chain. Since most amino acids have several codons at their disposal, this must mean that either there must be many more tRNAs than is absolutely necessary, or that some tRNAs can base pair with more than one codon. In fact, both scenarios are true. Some amino acids do have more than one tRNA but. Also, while the first two base pairs strictly have to be correctly base paired, in the third so-called wobble position of the codon, some mismatches and non-standard base pairs are tolerated. This also explains why often different codons for the same amino acid have the same bases in the first two positions."