Answer:
The correct answer is amino acids.
Step-by-step explanation:
Amino acids are the building blocks of protein molecule.An amino acid contain an amino group(-NH2) at one end and a carboxyl group at another ends.
The main structural difference occur among amino acidsis the presence of different side chains.
For example some amino acids contain aliphatic polar side chains,some contain aliphatic non polar side chain,some contain uncharged polar side chains,some contain positively charged side chains and rest of the others contain negatively charged side chain.