Final answer:
Out of 64 possible codons in the genetic code, 61 are assigned to amino acids, and three are stop signals. There are 20 common amino acids that are used in proteins.
Step-by-step explanation:
There are 64 possible codons in the genetic code, which are combinations of the four nucleotides (A, U, G, and C) in sets of three. Out of these, 61 codons encode for amino acids and the remaining three are stop codons that signal the end of protein synthesis. Furthermore, there are 20 common amino acids that are used in the proteins produced by organisms. Each three-letter codon corresponds to one particular amino acid or a stop signal during the protein synthesis process. The redundancy in this system allows for more than one codon to correspond to a single amino acid, which helps in making the code robust against mutations.