Question

Which of these is the smallest structure?
a. Protein
b. Polypeptide
c. Dipeptide
d. Amino acid

Answer 1

option D is the right answer .
This is because
 -amino acids build up proteins 
- two peptides make a dipeptide 
- polypeptide is made up of long chain of peptides .
-peptide is a short chain of amino acid monomers linked by amide bond . 

Answer 2

The answer is  d. Amino acid