Why is leucine amino acid used the most in proteins and tryptophan the least?

Question

The amino acid leucine, is used in proteins more than others. Leucine with 9.1 percent (its average in more than 1.150 different proteins) is used most and tryptophan with 1.4 percent is used less than all other amino acids. Why is leucine used more than tryptophan?

Answer 1

Hmmm. I can think of a couple of possibilities:

Tryptophan has only one codon that codes for it whereas leucine has five.

Tryptophan, with a ring structure, is larger than leucine which has a simple 3 carbon R group.