Each protein molecule is a polymer of which of the following?

The peptide chains loop,twist and fold back on themselves due to the formation of . . . . . . bonds to form a stable tertiary structure of protein.

Give scientific reason: Life is not possible without protein.

Which protein is present in the largest amount in the human body?

What does the part labeled '$X$' represent in the structural formula shown below?

Which amino acid contains a non-polar '$R$' group?