Proteins are made up of monomer units connected together. These units are called amino acids. Each amino acid has a carbonyl group and an amine group. These two groups will link when the amino acids are added. Also, an amino acid has a specific R group that characterizes which type of amino acid it is.
Carboxyl group + amino group + side chain. (https://www.coursehero.com/file/p628ngj/Question-3b-of-10-1-Proteins-560559-Maximum-Attempts-1-Question-Type-Multiple/)
