acid
substance that releases hydrogen ions (H+) when dissolved in water; an acidic solution has a pH less than 7.
activation energy
minimum amount of energy needed for reactants to form products in a chemical reaction.
active site
specific place where a substrate binds on an enzyme.
amino acid
small carbon compound joined by peptide bonds; building block of proteins.
atom
building block of matter; contains subatomic particles: neutrons, protons, and electrons.
base
substance that releases hydroxide ions (OH-) when dissolved in water; a basic solution has a pH greater than 7.
buffer
mixture that can react with an acid or a base to maintain the pH within a specific range.
carbohydrate
organic compound containing carbon, hydrogen, and oxygen in a ratio of one oxygen and two hydrogen atoms for each carbon atom.
catalyst
substance that speeds up a chemical reaction by reducing the needed amount of activation energy.
chemical reaction
energy-requiring process by which atoms or groups of atoms are changed into different substances.
compound
pure substance with unique properties; formed when two or more different elements combine.
covalent bond
type of chemical bond formed when atoms share electrons.
electron
negatively charged particle that orbits an atom's nucleus.
element
pure substance composed of only type of atom; cannot be broken down into another substance by physical or chemical means.
enzyme
protein that speeds up a biological reaction by lowering the amount of activation energy needed to start the reaction.
hydrogen bond
weak electrostatic bond formed by the attraction of opposite charges between a hydrogen atom and an oxygen, fluorine, or nitrogen atom.
ion
atom that is negatively or positively charged because it has lost or gained one or more electrons.
ionic bond
electrical attraction between two oppositely charged atoms or groups of atoms.
isotope
two or more atoms of the same element having different numbers of neutrons.
lipid
hydrophobic biological molecule composed mostly of carbon and hydrogen; fats, oils, and waxes are lipids.
macromolecule
large molecule formed by joining smaller organic molecules together.
mixture
combination of two or more different substances in which each substance keeps its individual characteristics; can have a uniform composition (homogeneous) or have distinct areas of substances (heterogeneous).
molecule
compound whose atoms are held together by covalent bonds.
neutron
particle without a charge in an atom's nucleus.
nucleic acid
complex macromolecule that stores and communicates genetic information.
nucleotide
a subunit of nucleic acid formed from a simple sugar, a phosphate group, and a nitrogen base.
nucleus
center of an atom; contains neutrons and protons.
pH
measure of the concentration of hydrogen ions (H+) in a solution; indicates the relative strength of an acid or a base: an acidic solution has a pH value less than 7, a basic solution has a pH value greater than 7, and pure water is neutral with a pH valu
polar molecule
molecule with oppositely charged regions.
polymer
large molecule formed from smaller repeating units of identical, or nearly identical, compounds linked by covalent bonds.
product
substance formed by a chemical reaction; located on the right side of the arrow in a chemical equation.
protein
organic compound made of amino acids joined by peptide bonds; primary building block of organisms.
proton
positively charged particle in an atom's nucleus.
reactant
substance that exists before a chemical reaction starts; located on the left side of the arrow in a chemical equation.
solute
substance dissolved in a solvent.
solution
homogeneous mixture formed when a substance (the solute) is dissolved in another substance (the solvent).
solvent
substance in which another substance is dissolved.
substrate
reactant to which an enzyme binds.
van der Waals forces
attractive forces between molecules.