Here's a breakdown:

* Amino Acids: These are the building blocks of proteins. There are 20 different types of amino acids commonly found in 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) - This is what differentiates the 20 amino acids from each other.

* Polypeptide Chain: Amino acids are linked together by peptide bonds to form long chains called polypeptide chains.

* Protein: A protein is a complex molecule composed of one or more polypeptide chains. The sequence of amino acids in a polypeptide chain determines the protein's unique three-dimensional structure, which in turn dictates its function.

In summary: Proteins are complex molecules built from a chain of amino acids linked together by peptide bonds. The sequence and arrangement of these amino acids determine the protein's specific shape and function.