Final answer:
64 codons exist that can specify amino acids in the genetic code, of which 61 are used to encode the 20 common amino acids and 3 are stop codons. A single amino acid can be encoded by multiple codons due to the degeneracy of the genetic code.
Step-by-step explanation:
There are 64 different codons that code for amino acids. Out of these, 61 codons encode for the 20 common amino acids and three are stop codons, signaling the end of protein synthesis. The large number of codons compared to amino acids is due to the degeneracy of the genetic code, meaning that a single amino acid can be encoded by more than one codon. For instance, the amino acid glycine is specified by four different codons: GGU, GGC, GGA, and GGG. On the other hand, Methionine and Tryptophan are unique in that they are each encoded by a single codon.
Each codon is composed of three nucleotides. This three-nucleotide sequence is necessary because a one-nucleotide sequence would only encode four amino acids and a two-nucleotide sequence would only encode 16 amino acids – both insufficient for the 20 amino acids that are commonly found in proteins.
The redundancy and the presence of a wobble position, which is the third nucleotide in a codon, allows for variations in the genetic code without altering the protein being produced, increasing the robustness of the genetic encoding system.