Answer: a, b The synthesis of protein involves conversion from a four-letter nucleotide language to one of 20 chemically distinct amino acids. This process is referred to as translation. There is no mechanism for direct chemical recognition between specific nucleic acid bases and specific amino acids. Instead, an adaptor molecule, tRNA, is used. Each tRNA carries only one amino acid and must be recognized by a distinct enzyme which catalyzes the covalent attachment of the carboxyl end of the amino acid to the end of the tRNA in a process using ATP. Protein synthesis occurs by the formation of a peptide bond between the carboxyl terminal of the growing peptide chain and the free amino acid of deactivated amino acid tRNA. This event does not occur in free solution, but within ribosomes. Ribosomes are protein synthesizing machines that bring all of the necessary components together in the correct sequence and spacial orientation. Protein synthesis consumes a great deal of energy because four high-energy phosphate bonds must be split to make each peptide bond. Complete synthesis of a single protein takes 30 seconds to a few minutes, but multiple ribosomes can initiate translation and be moving down the mRNA molecules simultaneously, thus increasing the rate of protein synthesis