2.6: Terms and Definitions

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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

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

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

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

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

Functional group

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

Hydrogen bond

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

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

Kinetic energy

energy that matter possesses because of its motion

Lipid

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

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

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

Organic compound

substance that contains both carbon and hydrogen

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

Polysaccharide

compound consisting of more than two carbohydrate monomers bonded by dehydration synthesis via glycosidic bonds

Potential energy

stored energy matter possesses because of the positioning or structure of its components

Product

one or more substances produced by a chemical reaction

Prostaglandin

lipid compound derived from fatty acid chains and important in regulating several body processes

Protein

class of organic compounds that are composed of many amino acids linked together by peptide bonds

Proton

heavy subatomic particle having a positive charge and found in the atom’s nucleus

Purine

nitrogen-containing base with a double ring structure; adenine and guanine

Pyrimidine

nitrogen-containing base with a single ring structure; cytosine, thiamine, and uracil

Radioactive isotope

unstable, heavy isotope that gives off subatomic particles, or electromagnetic energy, as it decays; also called radioisotopes

Reactant

one or more substances that enter into the reaction

Ribonucleic acid (RNA)

ribose-containing nucleotide that helps manifest the genetic code as protein

Solution

homogeneous liquid mixture in which a solute is dissolved into molecules within a solvent

Steroid

(also, sterol) lipid compound composed of four hydrocarbon rings bonded to a variety of other atoms and molecules

Substrate

reactant in an enzymatic reaction

Suspension

liquid mixture in which particles distributed in the liquid settle out over time

Synthesis reaction

type of anabolic reaction in which two or more atoms or molecules bond, resulting in the formation of a larger molecule

Triglyceride

lipid compound composed of a glycerol molecule bonded with three fatty acid chains

Valence shell

outermost electron shell of an atom