The units of proteins which unite in long chains to form proteins, are called as

Proteins are macromolecules made up of monomers called amino acids. The amino acid residues are joined together by peptide bonds to form proteins. The amino acids are compounds having both amino group and a carboxylic group bonded to same carbon atom called $\alpha$-carbon atom. Other atoms bonded to $\alpha$-carbon atom are a variable substituent group and a hydrogen atom.