Here's a breakdown:

* Amino Acids: These are the building blocks of proteins. They are small organic molecules that contain a central carbon atom bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom (-H), and a side chain (R group). The R group varies between different amino acids, giving them unique chemical properties.

* Peptide Bonds: Amino acids link together to form chains through peptide bonds. These bonds are formed between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water.

* Polypeptide Chain: A chain of multiple amino acids linked by peptide bonds is called a polypeptide chain.

* Protein: Proteins can be made up of one or more polypeptide chains that fold into complex three-dimensional structures. These structures are determined by the sequence of amino acids in the chain and are crucial for the protein's function.

So, the essence is: Amino acids are the fundamental units that form protein chains.