AP BIOLOGY

Detailed explanation-1: -Final answer: 61 codons out of 64 codes for 20 different amino acids. It is referred to as degeneracy of genetic code.

Detailed explanation-2: -There are 64 possible permutations, or combinations, of three-letter nucleotide sequences that can be made from the four nucleotides. Of these 64 codons, 61 represent amino acids, and three are stop signals.

Detailed explanation-3: -Of these 64 codons, 61 represent amino acids, and the remaining three represent stop signals, which trigger the end of protein synthesis. Because there are only 20 different amino acids but 64 possible codons, most amino acids are indicated by more than one codon.

Detailed explanation-4: -Because DNA consists of four different bases, and because there are three bases in a codon, and because 4 * 4 * 4 = 64, there are 64 possible patterns for a codon. Since there are only 20 possible amino acids, this means that there is some redundancy–several different codons can encode for the same amino acid.

Detailed explanation-5: -The number of potential triplets is 64. Subtracting for a necessary stop codon, organisms could code for up to 63 different amino acids. One could argue that 20 is simply good enough, but several species use up to 22 residues to synthesize proteins.