Here's why:

* Amino acids are the building blocks of proteins.

* Peptides are short chains of amino acids linked together by peptide bonds.

* Dipeptides specifically refer to peptides composed of two amino acids.

As the chain of amino acids gets longer, we have:

* Tripeptide (3 amino acids)

* Tetrapeptide (4 amino acids)

* Polypeptide (many amino acids)