Key Terms
Metabolism
All chemical reactions inside a cell. Metabolic pathways: series of stepwise, interconnected reactions.
Two types
Catabolism: breaks down complex molecules into simpler ones; releases energy; exergonic. Anabolism: builds complex molec
Autotrophs
Convert inorganic CO2 into organic carbon. Examples: plants, cyanobacteria.
Phototrophs
Energy from light. Chemotrophs: energy from chemical bonds.
Oxidation
Loss of electrons from a molecule. Reduction: gain of electrons by a molecule.
High-energy phosphate bonds
The bonds between phosphate groups in ADP and ATP. Unstable due to repulsion of negative charges.
Dephosphorylation
Removal of one phosphate (releasing inorganic phosphate, Pi) or two phosphates (releasing pyrophosphate, PPi) from ATP.
Enzyme
Pyruvate dehydrogenase (an enzyme complex). Reaction: pyruvate is decarboxylated — one carbon is lost as CO2.
Substrate
The molecule an enzyme binds. Active site: specific location on the enzyme where substrate binds.
Cofactors
Inorganic ions (e.g., iron Fe2+, magnesium Mg2+, zinc Zn2+) that stabilize enzyme conformation.
Coenzymes
Organic helper molecules; often derived from dietary vitamins. Reusable.
Apoenzyme
Enzyme without its necessary cofactor or coenzyme. Inactive.
Holoenzyme
Enzyme with the necessary cofactor or coenzyme. Active.
Allosteric activator
Binds away from the active site; induces a conformational change that increases enzyme affinity for its substrate.
Feedback inhibition
The end product of a metabolic pathway noncompetitively binds to an enzyme early in that pathway, slowing or stopping fu