Proteins: Large molecules made up of chains of amino acids, which perform a vast array of functions within organisms including catalyzing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another.
Peptide Bond: The chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O). This is a dehydration synthesis reaction.
Polypeptides: A chain or sequence of amino acids linked by peptide bonds. Polypeptides fold into specific three-dimensional structures - their so-called native state - which determine their activity or function in an organism.