active site

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

adenosine triphosphate (ATP)

biological unit of energy, which consists of an adenosine (an adenine group and a ribose sugar) and three phosphate groups

alpha helix

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

amino acid

protein-building molecule that contains an amino group (NH2{\rm{{-}NH}}_2 ), a carboxyl group (COOH\rm{{-}COOH} ), and between them a carbon atom attached to a side chain

beta pleated sheet

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


carbohydrate made of two monosaccharides


monosaccharide (simple sugar) used for energy in biological systems


hydrophobic macromolecule that may provide storage, structure, or nutrients in organisms


single (simple) sugar molecule

nucleic acid

large molecule made of nucleotides


organic compound that forms the basis of a genetic sequence, consisting of a sugar, a phosphate, and a nitrogenous base

peptide bond

covalent amide (CONH\rm{{-}CONH{-}}) bond that forms between two adjacent amino acids along the same peptide chain. The bond forms between the amine group of one amino acid and the carboxyl (COOH\rm{{-}COOH}) group of another.


lipid that usually consists of two fatty acid tails covalently linked to a common phosphate group


carbohydrate polymer consisting of many monosaccharides that form a long chain

primary structure

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

quaternary structure

two or more chains of proteins that interact with one another

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


lipid that contains a core with four fused ring structures (three 6- and one 5-membered ring) that serves as a precursor to hormones, cholesterol, or other molecules


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

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