activation energy

minimum energy needed for a chemical reaction to initiate

active site

place on an enzyme where the substrate binds and the reaction occurs

allosteric regulation

type of enzyme regulation in which the location at which the regulatory molecule binds is not the same as the active site

alpha helix

helical structure of proteins that adopts a right-handed-spiral conformation where chain backbone NH{\rm N{-}H} groups form hydrogen bonds with C=O{\rm {C{=}O}} groups of nearby amino acids along the protein chain

amino acid

organic molecule that contains a carboxyl group (COOH{-}{\rm{COOH}} ), an amino group (NH2{-}{\rm{NH}}_2), and a functional side chain, which is a group of atoms unique in its structure and function

amino group

portion of an amino acid made up of a nitrogen atom bonded to two hydrogen atoms (NH2{-}{\rm{NH}}_2)

beta sheet

structure of amino acids that takes the shape of a pleated sheet folded at regular intervals

carboxyl group

portion of a molecule made of a carbon atom bonded to one oxygen atom and one hydroxyl group (COOH{-}{\rm{COOH}})


substance that causes the rate of a chemical reaction to increase

competitive inhibitor

enzyme inhibitor in which the inhibitor binds to the active site


shape and configuration of a protein backbone and side chains


substance, usually a protein, that speeds up a biological reaction without being consumed in the reaction

feedback inhibition

type of enzyme inhibition in which an increasing concentration of product inhibits the enzyme activity, stopping the reaction


molecule (other than the products of the reaction) that decreases the rate of reaction

metabolic pathway

series of chemical reactions that occur in a living organism and may be facilitated by enzymes. The products of one set of enzymatic reactions serve as the reactants for a different enzymatic reaction.

noncompetitive inhibition

type of enzyme inhibition in which the inhibitor does not bind to the active site and may bind to either the enzyme or the enzyme-substrate complex

peptide bond

covalent bond formed between an amino group and a carboxyl group on neighboring amino acids

polypeptide chain

linear molecule consisting of amino acids connected by peptide bonds

primary structure

sequence of amino acids linked by peptide (amide) bonds to form a polypeptide chain

quaternary structure

two or more polypeptide chains that interact with one another

R group

one of the 20 possible groups that give amino acids their distinct chemical identities

secondary structure

structure of a protein that is the initial folding of the amino acid polymer that arises from hydrogen bonding between the amine and carboxyl groups of amino acids in neighboring parts of the chain


molecule that is acted upon by an enzyme by binding to the enzyme's active site


single polypeptide chain that is part of a larger, multi-subunit protein

tertiary structure

structure of a protein produced by interactions between the R groups of the amino acids in the chain and with the environment around them