The differences between polypeptides and proteins are incredibly significant. Polypeptides are covalently bound amino acids via a phosphate bond. This phosphate bond is always the same between amino acids regardless of the amino acid. The bond is the same because all amino acids have an identical alpha amino group and an alpha carboxyl group. The peptide bond forms via dehydration, you can break the bond with the use of hydrolysis. The peptide bond forms between the alpha carboxyl group of the “old” amino acid and the alpha amino group of the “new” amino acid. When multiple amino acids are bound together in this fashion they form a polypeptide chain. Proteins are made up of one or more of these polypeptide chains which are referred to as subunits. Proteins employ different types of bonding, they use noncovalent bonding. Noncovalent bonds don’t share electrons rather they are electrostatic interactions. This means that atoms interact based off of charge differences. Proteins fold based off of the charge of certain R groups of amino acids and the noncovalent interactions that they form. Proteins can even make disulfide bonds if two cysteine amino acid R groups interact in the polypeptide chain. So the main difference between proteins and polypeptides is that proteins are made up of polypeptides, not vice versa.
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