Here's a breakdown:

* Amino acids are the building blocks of proteins. Each amino acid has a central carbon atom bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a unique side chain (R group).

* Peptide bond is a covalent bond formed between the carboxyl group of one amino acid and the amino group of another amino acid. This reaction releases a water molecule.

* Polypeptide chain is a chain of amino acids linked together by peptide bonds.

Think of it like building a chain out of links. Each amino acid is a link, and the peptide bond is what connects the links together to form the chain.