The thymine analog 5-bromouracil is a chemical mutagen that induces single base-pair substitutions in DNA called transitions (substitutions of one purine for another purine and one pyrimidine for another pyrimidine). Using the known nature of the genetic code (Table 12.1), which of the following amino acid substitutions should you expect to be induced by 5-bromouracil with the highest frequency:
(a) Met → Val; 

(b) Met → Leu; 

(c) Lys → Thr;

(d) Lys → Gln; 

(e) Pro → Arg; or 

(f) Pro → Gln? Why?