Here's why:

* Proteins are polymers: They are long chains made up of smaller, repeating units called monomers.

* Amino acids are the monomers of proteins: Each amino acid has a central carbon atom bonded to:

* An amino group (-NH2)

* A carboxyl group (-COOH)

* A hydrogen atom (-H)

* A side chain (R group) that varies between different amino acids.

* Peptide bonds: Amino acids are linked together by peptide bonds, which form between the carboxyl group of one amino acid and the amino group of the next.

So, proteins are essentially chains of amino acids linked together in specific sequences. The unique order and arrangement of these amino acids determine the shape and function of each protein.