Explain the relationship between polypeptides and proteins .

Peptide bonds, and proteins. Amino acids are the monomer building blocks of proteins. When two are joined together in a peptide bond, they form proteins.A polypeptide is amino acids that bond to each other one at a time to form a long chain held together by peptidebonds

.Polypeptides and proteins are natural and essential organic compounds of a cell. They are both composed of amino-acids. Amino-acids are naturally occurring compounds which link together to form peptides, polypeptides, and proteins. Each amino-acid contains one amine (-NH2) and one hydroxyl (-COOH) group, as well as a specific side chain (R group). The side chain group varies in size, shape, charge, and reactivity, and is therefore unique to each amino-acid. There are 20 types of monomeric amino-acids capable of linking together in different combinations, thus conferring polypeptides and proteins with a high diversity.

A polypeptide is a polymer with a defined sequence of amino-acids linked together through covalent peptide bonds. A peptide bond is the result of a condensation reaction between two amino-acids: the carboxyl group of one amino-acid reacts with the amino group of an adjacent amino-acid, releasing a molecule of water (H2O).  

Proteins are structurally and functionally complex molecules. The term protein is used to describe the three-dimensional structure formed by the folding of one or more polypeptides. Proteins present four levels of structural organization, with the polypeptide being the primary structure. A protein has a secondary structure when polypeptide chains form α helices and β sheets.