A peptide is nothing more than a string of amino acids that is similar to, but not identical to, a protein. To understand what a peptide is and how it differs from a protein, it is necessary to first understand what an amino acid is.
What Are Amino Acids?
Amino acids are biologically important molecules, but not all of them are used by living organisms. In fact, the human body requires only 20 different amino acids to function (the case for almost all living things), even though nearly 500 have been identified in the universe so far. Amino acids have two specific chemical structures, called amine and carboxylic acid groups, at opposite ends. These structures endow amino acids with a common set of functions and define how they interact with one another and with other molecules.