Final answer:
The 64 possible codons arise from the combinations of three nucleotides. With degeneracy in the genetic code, some amino acids are represented by multiple codons. This redundancy, especially with the 'wobble' position, helps protect against mutations.
Step-by-step explanation:
There are 64 possible codons due to the different combinations of the four nucleotides that make up the genetic code (adenine, uracil, cytosine, guanine). These nucleotides can be arranged in sets of three, creating 43 or 64 unique triplets. However, there are only 20 common amino acids that proteins are built from. This discrepancy is due to the genetic code being degenerate, meaning that some amino acids are specified by more than one codon.
The genetic code also includes three stop codons that do not code for any amino acid but instead signal the end of a polypeptide chain. The redundancy of having multiple codons for a single amino acid can make the cell's translational machinery more robust to mutations, especially if the mutation occurs in the third, or 'wobble', position of a codon. This wobble hypothesis explains the degeneracy of the genetic code, and the fact that not all 64 codons are equal in terms of their specificity. They are arranged such that if a mutation occurs, there is a higher probability that the altered codon will still code for the same amino acid, or at least for one with similar properties, which can reduce the impact of mutations on protein function.