AP BIOLOGY

Detailed explanation-1: -Codons are made up of any triplet combination of the four nitrogenous bases adenine (A), guanine (G), cytosine (C), or uracil (U). Of the 64 possible codon sequences, 61 specify the 20 amino acids that make up proteins and three are stop signals.

Detailed explanation-2: -But three DNA letters provide more than enough combinations to code for all twenty amino acids. So three was the answer. It was a triplet code.

Detailed explanation-3: -The triplets of nitrogenous bases in DNA that code for amino acids are called codons. There are 64 codons, 61 of which code for different amino acids.

Detailed explanation-4: -Thus, the smallest combination of four bases that could encode all 20 amino acids would be a triplet code. However, a triplet code produces 64 (43 = 64) possible combinations, or codons.

Detailed explanation-5: -Because there are only 20 different amino acids but 64 possible codons, most amino acids are indicated by more than one codon. (Note, however, that each codon represents only one amino acid or stop codon.)