Suppose that you have a protein‑synthesis system that is synthesizing a protein designated a. furthermore, you know that protein a has four equally spaced trypsin cleavage sites that, on digestion with trypsin, yield the peptides a1, a2, a3, a4, and a5 in sequence. you determine that peptide a1 is the amino‑terminal peptide and a5 is the carboxyl‑terminal peptide. finally, you know that your system requires four minutes to synthesize a complete protein a.

you decide to perform a labeling experiment. while the protein‑synthesis system is incubating, you add all 20 amino acids, each labeled with 14c. you designate the time you add these amino acids as t equals 0.

at t equals 1 min, you isolate intact protein a from the system, cleave it with trypsin, and isolate the peptides a1, a2, a3, a4, and a5.

q 1: which peptide is most heavily labeled with 14c at t equals 1 min? choices: a1, a2, a3, a4, or a5, (only one is correct)

at t equals 3 min, you isolate intact protein a again and digest it with trypsin to yield the five peptides. q 2: arrange the peptides in order from the most heavily labeled with 14c to the least labeled.

bank includes: a1, a2, a3, a4, a5

q 3: which statement best explains the results of this experiment? choices below (only one is correct)

the synthesis of protein a occurs in the amino to carboxyl direction.

the synthesis of protein a occurs in the 5′ to 3′ direction.

the synthesis of protein a requires 14c to proceed.

labeling the trypsin digestion fragments enables their separation by size.

the synthesis of protein a occurs in the carboxyl to amino direction.