Unit 3 AP Biology Vocabulary

These flashcards cover key vocabulary terms related to biochemical processes and metabolism, including definitions relevant to enzymes, energy transfer, and cellular processes.

Activation energy

The minimum amount of energy required to start a chemical reaction.

Active site

The specific region of an enzyme where the substrate binds and the reaction occurs.

Allosteric site

A regulatory site on an enzyme where molecules bind to change enzyme shape and activity.

Anabolic (anabolism)

Metabolic pathways that build complex molecules from simpler ones; require energy input.

ATP

The main energy currency of the cell; stores and releases energy through phosphate group transfer.

Catabolic (catabolism)

Metabolic pathways that break down complex molecules into simpler ones; release energy.

Catalyst

A substance that speeds up a reaction without being consumed; enzymes are biological catalysts.

Competitive inhibitor

A molecule that competes with the substrate for the enzyme’s active site.

Denatured

When a protein loses its shape (due to heat, pH, etc.), causing loss of function.

Endergonic reaction

A reaction that requires energy input; products have more energy than reactants.

Entropy

A measure of disorder or randomness in a system.

Enzyme

A protein that speeds up biochemical reactions by lowering activation energy.

Exergonic reaction

A reaction that releases energy; products have less energy than reactants.

Metabolic pathway

A series of enzyme-controlled reactions that convert a starting molecule into a product.

Metabolism

The sum of all chemical reactions (anabolic + catabolic) in an organism.

Noncompetitive inhibitor

A molecule that binds to an allosteric site, changing enzyme shape and reducing activity.

Product

A molecule produced by a chemical reaction.

Reactant

A starting molecule that enters a chemical reaction.

Substrate

The specific reactant that an enzyme acts on.

Autotroph

An organism that makes its own food using energy from sunlight or chemicals.

Calvin cycle

The light-independent cycle in the stroma that uses CO₂, ATP, and NADPH to build sugars.

Carbon fixation

The incorporation of CO₂ into organic molecules during the Calvin cycle.

Chemiosmosis

Movement of H⁺ ions across a membrane to power ATP synthase and produce ATP.

Chlorophyll

The main pigment in chloroplasts that absorbs light energy for photosynthesis.

Electron transport chain (ETC)

A series of proteins that pass electrons and pump H⁺ to create a gradient.

Grana

Stacks of thylakoids inside a chloroplast.

Light-dependent reactions

Occur in the thylakoid membranes; use light to split water, make ATP, and produce NADPH.

Light-independent reactions

The Calvin cycle; use ATP and NADPH to convert CO₂ into sugars in the stroma.

Lumen

The internal space of the thylakoid where H⁺ ions accumulate during the light-dependent reactions.

NADPH / NADP⁺

NADP⁺ is an electron carrier; NADPH carries high-energy electrons to the Calvin cycle.

Oxidation

Loss of electrons from a molecule.

Photosynthesis

The process by which autotrophs convert light energy into chemical energy stored in sugars.

Photosystem

A protein-pigment complex in the thylakoid membrane that absorbs light and energizes electrons.

Reduction

Gain of electrons by a molecule.

Stroma

The fluid-filled space of the chloroplast where the Calvin cycle occurs.

Thylakoid

A membrane-bound sac inside chloroplasts where the light-dependent reactions occur.

Aerobic

Processes that require oxygen.

Anaerobic

Processes that occur without oxygen.

Cell respiration

Breaks down glucose to produce ATP; includes glycolysis, Krebs cycle, and oxidative phosphorylation.

Cristae

Folds of the inner mitochondrial membrane that increase surface area for the ETC.

FADH₂ / FAD⁺

FAD⁺ is an electron carrier; FADH₂ carries electrons to the ETC.

Fermentation

Anaerobic process that regenerates NAD⁺ so glycolysis can continue; produces lactic acid or ethanol.

Glycolysis

First step of respiration; breaks glucose into pyruvate in the cytosol, producing ATP and NADH.

Heterotroph

An organism that obtains energy by consuming other organisms.

Intermembrane space

Space between the inner and outer mitochondrial membranes where H⁺ accumulates.

Krebs cycle

Occurs in the mitochondrial matrix; produces CO₂, ATP, NADH, and FADH₂.

Matrix

Innermost compartment of the mitochondrion where the Krebs cycle occurs.

NADH / NAD⁺

NAD⁺ is an electron carrier; NADH carries high-energy electrons to the ETC.