Final answer:
The genetic code is triplet, meaning that each amino acid is coded for by three nucleotide bases in mRNA, known as a codon. There are 64 codons, 61 code for amino acids and 3 are stop codons.
Step-by-step explanation:
The genetic code is said to be triplet, meaning that there are 3 bases in mRNA that code for an amino acid (AA). This is represented by the letter 'b' in the provided choices. In the genetic code, each amino acid is specified by a sequence of three nucleotides, known as a codon. For example, if the mRNA codon is CUA, it will pair with a tRNA carrying the complementary anticodon GAU, which is attached to the amino acid leucine.
The code is both universal and degenerate. Being degenerate means that there are more codons (64) than there are amino acids to be coded for (20), allowing for multiple codons to specify the same amino acid. Of the 64 codons, three are stop codons that signal the end of protein synthesis, leaving 61 codons to code for amino acids, including the start codon AUG, which also codes for the amino acid methionine.