Glossary


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A

acid

compound that releases hydrogen ions (H+) in solution


activation energy

amount of energy greater than the energy contained in the reactants, which must be overcome for a reaction to proceed


adenosine triphosphate (ATP)

nucleotide containing ribose and an adenine base that is essential in energy transfer


amino acid

building block of proteins; characterized by an amino and carboxyl functional groups and a variable side-chain


anion

atom with a negative charge


atom

smallest unit of an element that retains the unique properties of that element


atomic number

number of protons in the nucleus of an atom


B

base

compound that accepts hydrogen ions (H+) in solution


bond

electrical force linking atoms


buffer

solution containing a weak acid or a weak base that opposes wide fluctuations in the pH of body fluids


C

carbohydrate

class of organic compounds built from sugars, molecules containing carbon, hydrogen, and oxygen in a 1-2-1 ratio


catalyst

substance that increases the rate of a chemical reaction without itself being changed in the process


cation

atom with a positive charge


chemical energy

form of energy that is absorbed as chemical bonds form, stored as they are maintained, and released as they are broken


colloid

liquid mixture in which the solute particles consist of clumps of molecules large enough to scatter light


compound

substance composed of two or more different elements joined by chemical bonds


concentration

number of particles within a given space


covalent bond

chemical bond in which two atoms share electrons, thereby completing their valence shells


D

decomposition reaction

type of catabolic reaction in which one or more bonds within a larger molecule are broken, resulting in the release of smaller molecules or atoms


denaturation

change in the structure of a molecule through physical or chemical means


deoxyribonucleic acid (DNA)

deoxyribose-containing nucleotide that stores genetic information


disaccharide

pair of carbohydrate monomers bonded by dehydration synthesis via a glycosidic bond


disulfide bond

covalent bond formed within a polypeptide between sulfide groups of sulfur-containing amino acids, for example, cysteine


E

electron

subatomic particle having a negative charge and nearly no mass; found orbiting the atom’s nucleus


electron shell

area of space a given distance from an atom’s nucleus in which electrons are grouped


element

substance that cannot be created or broken down by ordinary chemical means


enzyme

protein or RNA that catalyzes chemical reactions


exchange reaction

type of chemical reaction in which bonds are both formed and broken, resulting in the transfer of components


F

functional group

group of atoms linked by strong covalent bonds that tends to behave as a distinct unit in chemical reactions with other atoms


H

hydrogen bond

dipole-dipole bond in which a hydrogen atom covalently bonded to an electronegative atom is weakly attracted to a second electronegative atom


I

inorganic compound

substance that does not contain both carbon and hydrogen


ion

atom with an overall positive or negative charge


ionic bond

attraction between an anion and a cation


isotope

one of the variations of an element in which the number of neutrons differ from each other


K

kinetic energy

energy that matter possesses because of its motion


L

lipid

class of nonpolar organic compounds built from hydrocarbons and distinguished by the fact that they are not soluble in water


M

macromolecule

large molecule formed by covalent bonding


mass number

sum of the number of protons and neutrons in the nucleus of an atom


matter

physical substance; that which occupies space and has mass


molecule

two or more atoms covalently bonded together


monosaccharide

monomer of carbohydrate; also known as a simple sugar


N

neutron

heavy subatomic particle having no electrical charge and found in the atom’s nucleus


nucleotide

class of organic compounds composed of one or more phosphate groups, a pentose sugar, and a base


O

organic compound

substance that contains both carbon and hydrogen


P

peptide bond

covalent bond formed by dehydration synthesis between two amino acids


periodic table of the elements

arrangement of the elements in a table according to their atomic number; elements having similar properties because of their electron arrangements compose columns in the table, while elements having the same number of valence shells compose rows in the table


pH

negative logarithm of the hydrogen ion (H+) concentration of a solution


phospholipid

a lipid compound in which a phosphate group is combined with a diglyceride


phosphorylation

addition of one or more phosphate groups to an organic compound


polar molecule

molecule with regions that have opposite charges resulting from uneven numbers of electrons in the nuclei of the atoms participating in the covalent bond



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