Biology Terms

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A substance that increases the hydrogen ion concentration of a solution.

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acid

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Rain, snow, or fog that is more acidic than pH 5.6.

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acid precipitation

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The amount of energy that reactants must absorb before a chemical reaction will start.

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activation energy

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The specific portion of an enzyme that attaches to the substrate by means of weak chemical bonds.

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active site

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Organic compounds containing hydroxyl groups.

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alcohols

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The attraction between different kinds of molecules.

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adhesion

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An organic molecule with a carbonyl group located at the end of the carbon skeleton.

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aldehyde

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A specific receptor site on some part of an enzyme molecule remote from the active site.

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allosteric site

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A spiral shape constituting one form of the secondary structure of proteins, arising from a specific hydrogen-bonding structure.

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alpha helix

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An organic compound with one or more amino groups.

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amine

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An organic molecule possessing both carboxyl and amino groups. Amino acids serve as the monomers of proteins.

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amino acid

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A functional group that consists of a nitrogen atom bonded to two hydrogen atoms; can act as a base in solution, accepting a hydrogen ion and acquiring a charge of +1.

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amino group

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A metabolic pathway that synthesizes a complex molecule from simpler compounds.

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anabolic pathway

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A negatively charged ion.

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anion

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A solution in which water is the solvent.

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aqueous solution

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The smallest unit of matter that retains the properies of an element.

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atom

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An atom's central core, containing protons and neutrons.

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atomic nucleus

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The number of protons in the nucleus of an atom, unique for each element and designated by a subscript to the left of the elemental symbol.

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atomic number

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The total atomic mass, which is the mass in grams of one mole of the atom.

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atomic weight

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An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.

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ATP (adenosine triphosphate)

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A substance that reduces the hydrogen ion concentration of a solution.

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base

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One form of the secondary structure of proteins ni which the polypeptide chain folds back and forth, or where two regions of the chain lie parallel to each other and are held together by hydrogen bonds.

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beta pleated sheet

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The study of how organisms manage their energy resources.

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bioenergetics

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A substance that consists of acid and base forms in a solution and that minimizes changes in pH when extraneous acids or bases are added to the solution.

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buffer

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The amount of heat energy required to raise the temperature of 1g of water by 1°C; also the amount of heat energy that 1g of water releases when it cools by 1°C. The Calorie (with a capital C), usually used to indicate the energy content of food, is a kilocalorie.

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calorie (cal)

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A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides).

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carbohydrate

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A functional group present in aldehydes and ketones and consisting of a carbon atom double-bonded to an oxygen atom.

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carbonyl group

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A functional group present in organic acids and consisting of a single carbon atom double-bonded to an oxygen atom and also bonded to a hydroxyl group.

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carboxyl group

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An organic compound containing a carboxyl group.

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carboxylic acid

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A metabolic pathway that releases energy by breaking down complex molecules to simpler compounds.

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catabolic pathway

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A chemical agent that changes the rate of a reaction without being consumes by the reaction.

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catalyst

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An ion with a positive charge, produced by the loss of one or more electrons.

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cation

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A structural polysaccharide of cell walls, consisting of glucose monomers joined by beta-1,4-glycosidic linkages.

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cellulose

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A temperature scale (°C) equal to 5/9 (°F-32) that measures the freezing point of water at 0°C and the boling point of water at 100°C.

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Celsius scale

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Protein molecules that assist the proper folding of other proteins.

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chaperonin

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An attraction between two atoms resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms; the bonded atoms gain complete electron shells.

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chemical bond

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Energy stored in the chemical bonds of molecules; a form of potential energy.

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chemical energy

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In a reversible chemical reaction, the point at which the rate of the forward reaction equals the rate of the reverse reaction.

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chemical equilibrium

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A process leading to chemical changes in matter; involves the making of and/or breaking of chemical bonds.

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chemical reaction

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A structural polysaccharide of an amino sugar found in many fungi and in the exoskeletons of all arthropods.

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chitin

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A steroid that forms an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other biologically important steroids.

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cholesterol

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An organic molecule serving as a cofactor. Most vitamins function as coenzymes in important metabolic reactions.

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coenzyme

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Any nonprotein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely with the substrate during catalysis.

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cofactor

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The binding together of like molecules, often by hydrogen bonds.

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cohesion

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A substance that reduces the activity of an enzyme by entering the active site in place of the substrate whose structure it mimics.

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competitive inhibitor

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A substance consisting of two or more elements in a fixed ratio.

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compound

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A reaction in which two molecules become covalently bonded to each other through the loss of a small molecule, usually water; also called dehydration reaction.

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condensation reaction

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An interaction of the constituent subunits of a protein whereby a conformational change in one subunit is transmitted to all the others.

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cooperativity

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A type of strong chemical bond in which two atoms share one pair of valence electrons.

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covalent bond

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A measure of mass for atoms and subatomic particles.

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dalton

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A chemical reaction in which two molecules covalently bond with each other with the removal of a water molecule.

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dehydration reaction

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For proteins, a process in which a protein unravels and loses its native conformation, thereby becoming biologically inactive. For DNA, the separation of the two strands of the double helix. Denaturation occurs under extreme conditions of pH, salt concentration, and temperature.

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denaturation

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A double-stranded, helical nucleic acid molecule capable of replicating and determining the inherited structure of a cell's proteins.

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deoxyribonucleic acid (DNA)

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The sugar component of DNA, having one less hydroxyl group than ribose, the sugar component of RNA.

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deoxyribose

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A double sugar, consisting of two monosaccharides joined by dehydration synthesis.

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disaccharide

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Strong covalent bonds formed when the sulfur of one cysteine monomer bonds to the sulfer of another cysteine monomer.

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disulfide bridge

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A type of covalent bond in which two atoms share two pairs of electrons; symbolized by a pair of lines between the bonded atoms.

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double covalent bond

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The form of native DNA, referring to its two adjacent polynucleotide strands wound into a spiral shape.

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double helix

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A subatomic particle with a single negative charge; one or more electrons move around the nucleus of an atom.

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electron

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The attraction of an atom for the electrons of a covalent bond.

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electronegativity

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An energy level representing the distance of an electron from the nucleus of an atom.

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electron shell

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Any substance that cannot be broken down to any other substance.

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element

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Molecules that are mirror images of each other.

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enantiomers

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A nonspontaneous chemical reaction in which free energy is absorbed from the surroundings.

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endergonic reaction

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The capacity to do work (to move matter against an opposing force).

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energy

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In cellular metabolism, the use of energy released from an exergonic reaction to drive an endergonic reaction.

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energy coupling

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The different states of potential energy for electrons in an atom.

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energy level

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A quantitative measure of disorder or randomness, symbolized by S.

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entropy

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A protein serving as a catalyst, a chemical agent that changes the rate of a reaction without being consumed by the reaction.

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enzyme

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The property of a liquid whereby the surface becomes cooler during evaporation, owing to a loss of highly kinetic molecules to the gaseous state.

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evaporative cooling

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A spontaneous chemical reaction in which there is a new release of free energy.

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exergonic reaction

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A biological compound consisting of three fatty acids linked to one glycerol molecule.

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fat (triacylglycerol)

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A long carbon chain carboxylic acid. Fatty acids vary in length and location of double bonds; three fatty acids linked to a glycerol molecule form fat.

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fatty acid

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A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.

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feedback inhibition

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The principle of conservation of energy. Energy can be transferred and transformed, but it cannot be created or destroyed.

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first law of thermodynamics

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The portion of a system's energy that can perform work when temperature is uniform throughout the system. The change in free energy of a system is calculated by the equation ΔG = ΔH - TΔS, where T is absolute temperature.

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free energy

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The initial investment of energy necessary to start a chemical reaction; also called activation energy.

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free energy of activation

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A specific configuration of atoms commonly attached to the carbon skeletons of organic molecules and usually involved in chemical reactions.

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functional group

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A discrete nit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).

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gene

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Compounds that have the same molecular formula but differ in the spatial arrangements of their atoms.

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geometric isomers

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An extensively branched glucose storage polysaccharide found in thel iver and muscle of animals; the animal equivalent of starch.

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glycogen

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A covalent bond formed between two monosaccarides by a dehydration reaction.

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glycosidic linkage

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The total amount of kinetic energy due to molecular motion in a body of matter. Heat is energy in its most random form.

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heat

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The quantity of heat a liquid must absorb for 1 gram of it to be converted from the liquid to the gaseous state.

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heat of vaporization

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The sphere of water molecules around each dissolved ion.

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hydration shell

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An organic molecule consisting only of carbon and hydrogen.

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hydrocarbon

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A type of weak chemical bond formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule.

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hydrogen bond

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A single proton with a charge of +1. The dissociation of a water molecule (H₂O) leads to the generation of a hydroxide ion (OH-) and a hydrogen ion (H+).

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hydrogen ion