unit 3 AP Biology

Catabolic pathways

Metabolic routes that break down molecules into smaller units, releasing energy.

Anabolic pathways

Metabolic routes that build complex molecules from simpler ones, consuming energy.

First law of thermodynamics

Energy cannot be created or destroyed, only transformed or transferred.

Free energy

The portion of a system’s energy available to do work.

Exergonic reaction

A chemical reaction that releases energy; spontaneous.

Endergonic reaction

A chemical reaction that absorbs energy; non-spontaneous.

Adenosine triphosphate (ATP)

The main energy currency of the cell.

Phosphorylated

A molecule that has received a phosphate group, often activating or energizing it.

Enzyme

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

Activation energy

The energy required to start a chemical reaction.

Substrate

The reactant that an enzyme acts upon.

Enzyme-substrate complex

Temporary structure formed when an enzyme binds its substrate.

Active site

The region of an enzyme where the substrate binds.

Induced fit

The enzyme changes shape slightly to better fit the substrate.

Competitive inhibitors

Molecules that compete with the substrate for the active site.

Noncompetitive inhibitors

Molecules that bind elsewhere on the enzyme, altering its shape and function.

Allosteric regulation

Regulation of an enzyme by binding a molecule at a site other than the active site.

Fermentation

Anaerobic process that generates ATP without oxygen.

Aerobic respiration

ATP production using oxygen; includes glycolysis, citric acid cycle, and oxidative phosphorylation.

Redox reactions

Chemical reactions involving the transfer of electrons

Electron transport chain

Series of proteins in mitochondria that transfer electrons and pump protons to generate ATP.

Glycolysis

First step of cellular respiration; breaks glucose into pyruvate.

Citric acid cycle

Second step; completes breakdown of glucose and produces electron carriers.

Oxidative phosphorylation

Final step; uses electron transport chain and chemiosmosis to make ATP.

ATP synthase

Enzyme that makes ATP using the proton gradient.

Chemiosmosis

Movement of protons across a membrane to drive ATP synthesis.

Alcohol fermentation

Produces ethanol and CO₂ from pyruvate in yeast.

Lactic acid fermentation

Produces lactate from pyruvate in muscle cells.

Cristae

Folds of the inner mitochondrial membrane where the electron transport chain occurs.

Matrix

Fluid-filled space inside mitochondria where the citric acid cycle takes place.

Autotrophs

Organisms that produce their own food using light or chemical energy.

Heterotrophs

Organisms that consume other organisms for energy.

Chlorophyll

Green pigment that captures light energy for photosynthesis.

Stomata

Pores on leaves that allow gas exchange.

Stroma

Fluid inside chloroplasts where the Calvin cycle occurs.

Thylakoids

Membrane sacs in chloroplasts where light reactions take place.

Light reactions

First stage of photosynthesis; converts light energy to chemical energy (ATP and NADPH).

Calvin cycle

Second stage; uses ATP and NADPH to fix carbon and produce glucose.

Carbon fixation

Incorporation of CO₂ into organic molecules.

Rubisco

Enzyme that catalyzes carbon fixation in the Calvin cycle.

C3 plants

Plants that fix carbon directly through the Calvin cycle; most common type.

Photorespiration

Wasteful process where Rubisco binds oxygen instead of CO₂.

C4 plants

Plants that fix carbon into a 4-carbon compound to minimize photorespiration.

CAM plants

Plants that fix carbon at night to conserve water in arid environments.