Proteins are long molecules built from various combinations of amino acids.

Here's the breakdown:

* Amino acids: These are the building blocks of proteins. There are 20 different amino acids commonly found in proteins.

* Polypeptide chain: Amino acids are linked together in a chain, forming a polypeptide chain. This chain can be hundreds or even thousands of amino acids long.

* Protein: A protein is one or more polypeptide chains folded into a specific three-dimensional shape.

The specific sequence of amino acids in a protein determines its unique structure and function. It's like a code that tells the protein how to fold and what job it will do.