Question

how many of the amino acids in the polypeptide below have an r group (side chain) that is only a hydrogen (h) atom? one none two three more than three

Explanation:

Step1: Identify R - groups

For the first amino - acid, R group is $CH_3$. For the second, R group is $CH_2SH$. For the third, R group is $H$.

Step2: Count R - groups with only H

Only one R - group is just a hydrogen atom.

Answer:

one