Glossary: Part 1 Photosynthesis

active site

A specific region of an enzyme (generally near the surface) that accepts one or more substrates and catalyzes a chemical reaction. Compare with allosteric site.

adenosine triphosphate (ATP)

(a–den’–oh–seen) An organic compound containing adenine - ribose - and three phosphate groups -- of prime importance for energy transfers in cells.

catalyst

(kat’–ah–list) A substance that increases the speed at which a chemical reaction occurs without being used up in the reaction. Enzymes are biological catalysts.

coenzyme

(koh–en’–zime) An organic cofactor for an enzyme -- generally participates in the reaction by transferring some component - such as electrons or part of a substrate molecule.

coupled reactions

A set of reactions in which an exergonic/exothermic reaction provides the free energy required to drive an endergonic/endothermic reaction -- energy coupling generally occurs through a common intermediate.

energy

The capacity to do work -- expressed in kilojoules or kilocalories.

entropy

(en’–trop–ee) Disorderliness -- a quantitative measure of the amount of the random - disordered energy that is unavailable to do work.

enzyme

(en’–zime) An organic catalyst (usually a protein) that accelerates a specific chemical reaction by lowering the activation energy required for that reaction.

FAD/FADH2

Oxidized and reduced forms - respectively - of flavin adenine dinucleotide - a coenzyme that transfers electrons (as hydrogen) in metabolism - including cellular respiration.

first law of thermodynamics

The law of conservation of energy - which states that the total energy of any closed system (any object plus its surroundings - i.e. - the universe) remains constant. Compare with second law of thermodynamics.

Half-reaction

one of two parts of a redox reaction - one of which involves a loss of electrons and the other of which involves a gain of electrons

heat

The total amount of kinetic energy in a sample of a substance.

heat energy

The thermal energy that flows from an object with a higher temperature to an object with a lower temperature.

kinetic energy

Energy of motion. Compare with potential energy.

NAD+/NADH

Oxidized and reduced forms - respectively - of nicotinamide adenine dinucleotide - a coenzyme that transfers electrons (as hydrogen) - particularly in catabolic pathways - including cellular respiration.

NADP+/NADPH

Oxidized and reduced forms - respectively - of nicotinamide adenine dinucleotide phosphate - a coenzyme that acts as an electron (hydrogen) transfer agent - particularly in anabolic pathways - including photosynthesis.

Oxidation

the part of an oxidation-reduction reaction in which there is a loss of electrons by a species or an increase in the oxidation number of an atom

Oxidation-reduction reaction (redox reaction)

a reaction in which electrons are transferred between species or in which atoms change oxidation number.

phosphorylation

(fos”–for–ih–lay’–shun) The introduction of a phosphate group into an organic molecule.

potential energy

Stored energy -- energy that can do work as a consequence of its position or state. Compare with kinetic energy.

Reduction

the part of an oxidation-reduction reaction in which there is a gain of electrons by a species or a decrease of oxidation number of an atom

second law of thermodynamics

The physical law stating that the total amount of entropy in the universe continually increases. Compare with first law of thermodynamics.

thermodynamics

Principles governing energy transfer (often expressed in terms of heat transfer). See first law of thermodynamics and second law of thermodynamics.

work

Any change in the state or motion of matter.