Nitrogen is a component of

Proteins are building blocks of the body. The proteins are made up of amino acids. The amino acids are linked together by peptide bonds to form a protein.The amino acids consist of amine group made up of nitrogen and hydrogen and the carboxyl group at the end and a side chain of R group which is specific to a particular amino acid. The amine group (NH${}_2$) is made up of nitrogen and hydrogen.

So, the correct answer is option A.