The energy required to raise a molecule to its transition state to undergo a chemical reaction.
active site
The region of an enzyme that binds substrates and catalyzes an enzymatic reaction.
allosteric regulation
The regulation of enzymes by small molecules that bind to a site distinct from the active site, changing the conformation and catalytic activity of the enzyme.
ATP (adenosine 5′-triphosphate)
An adenine-containing nucleoside triphosphate that serves as a store of free energy in the cell.
Calvin cycle
A series of reactions by which six molecules of CO2 are converted into glucose.
chlorophyll
The major photosynthetic pigment of plant cells.
citric acid cycle
A series of reactions in which acetyl CoA is oxidized to CO2. The central pathway of oxidative metabolism.
coenzyme
A low-molecular-weight organic molecules that work together with enzymes to catalyze biological reactions.
coenzyme A (CoA)
A coenzyme that functions as a carrier of acyl groups in metabolic reactions.
dark reactions
The series of reactions that convert carbon dioxide and water to carbohydrates during photosynthesis. See Calvin cycle.
electron transport chain
A series of carriers through which electrons are transported from a higher to a lower energy state.
enzyme
A protein or RNA that catalyzes a biological reaction.
feedback inhibition
A type of allosteric regulation in which the product of a metabolic pathway inhibits the activity of an enzyme involved in its synthesis.
flavin adenine dinucleotide (FADH2)
A coenzyme that functions as an electron carrier in oxidation/reduction reactions.
Gibbs free energy (G)
The thermodynamic function that combines the effects of enthalpy and entropy to predict the energetically favorable direction of a chemical reaction.
gluconeogenesis
The synthesis of glucose.
glycolysis
The anaerobic breakdown of glucose.
high-energy bond
A chemical bond that releases a large amount of free energy when it is hydrolyzed.
induced fit
A model of enzyme action in which the configurations of both the enzyme and the substrate are altered by substrate binding.
Krebs cycle
See citric acid cycle.
light reactions
The reactions of photosynthesis in which solar energy drives the synthesis of ATP and NADPH.
lock-and-key model
A model of enzyme action in which the substrate fits precisely into the enzyme active site.
nicotinamide-adenine dinucleotide (NAD+)
A coenzyme that functions as an electron carrier in oxidation/reduction reactions.
nitrogen fixation
The reduction of atmospheric nitrogen (N2) to NH3.
oxidative phosphorylation
The synthesis of ATP from ADP coupled to the energetically favorable transfer of electrons to molecular oxygen as the final acceptor in an electron transport chain.
phosphorylation
The addition of a phosphate group to a molecule.
photosynthetic pigment
A molecule that captures energy from sunlight by absorbing photons.
product
A compound formed as a result of an enzymatic reaction.
prosthetic group
A small molecule bound to a protein.
substrate
A molecule acted upon by an enzyme.
transition state
A high energy state through which substrates must pass during the course of an enzymatic reaction.
