AP Biology Unit 3: Cellular Energetics Comprehensive Guide

Enzyme

Biological macromolecules that act as catalysts, speeding up chemical reactions without being consumed.

Catalyst

A substance that increases the rate of a chemical reaction without undergoing permanent changes.

Active Site

The specific region on an enzyme where the substrate binds.

Substrate

The reactant molecule that an enzyme acts upon.

Enzyme-Substrate Complex

The temporary association formed when the substrate binds to the enzyme's active site.

Induced Fit Model

The model describing how the enzyme changes shape to fit the substrate during the reaction.

Activation Energy (E_a)

The initial energy investment required to start a reaction.

Exergonic Reaction

Releases energy; products have less free energy than reactants ($\Delta G < 0$).

Endergonic Reaction

Requires energy input; products have more free energy than reactants ($\Delta G > 0$).

Denaturation

Loss of an enzyme's functional shape due to temperature or pH changes.

Saturation Point

The point at which all active sites of an enzyme are occupied.

Competitive Inhibition

Inhibitor binds to the active site, blocking substrate binding.

Non-competitive Inhibition

Inhibitor binds to an allosteric site, changing enzyme shape and making the active site non-functional.

First Law of Thermodynamics

Energy cannot be created or destroyed, only transformed.

Second Law of Thermodynamics

Every energy transfer increases the entropy of the universe.

Energy Coupling

Using energy from an exergonic process to drive an endergonic one.

Adenosine Triphosphate (ATP)

A nucleotide that serves as the primary energy currency of the cell.

Photolysis

The splitting of water molecules during the light-dependent reactions of photosynthesis.

Electron Transport Chain (ETC)

A series of protein complexes that transfer electrons, leading to ATP production.

Chemiosmosis

The process of ATP generation using the proton gradient created by the ETC.

Calvin Cycle

The light-independent reactions of photosynthesis where carbon dioxide is fixed into glucose.

Rubisco

An enzyme that attaches CO2 to RuBP in the first step of the Calvin Cycle.

Glycolysis

The metabolic pathway that breaks down glucose into pyruvate.

Acetyl-CoA

The product of pyruvate conversion that enters the Krebs cycle.

Krebs Cycle

A chemical cycle used to load electron carriers with high-energy electrons.

Oxidative Phosphorylation

The stage of cellular respiration that produces most ATP through the ETC and chemiosmosis.

Fermentation

A process that allows ATP generation in the absence of oxygen by regenerating NAD+.

Alcoholic Fermentation

Conversion of pyruvate to ethanol and CO2 in anaerobic conditions.

Lactic Acid Fermentation

Conversion of pyruvate to lactate in anaerobic conditions.

Endothermy

The ability of some organisms to generate heat through the uncoupling of oxidative phosphorylation.

Ectothermy

The dependency of some organisms on external environmental heat sources for body temperature regulation.

LEO the lion says GER

Mnemonic for oxidation (lose electrons) and reduction (gain electrons).

C4 Pathway

A photosynthetic adaptation that minimizes water loss by spatial separation of CO2 fixation.

CAM Pathway

A photosynthetic adaptation that minimizes water loss by temporal separation of CO2 fixation.

ATP Synthase

An enzyme that catalyzes the formation of ATP from ADP and inorganic phosphate during chemiosmosis.

NADH

An electron carrier produced in glycolysis, the Krebs cycle, and during other metabolic reactions.

FADH2

Another electron carrier produced in the Krebs cycle.

Entropy

A measure of disorder in a system, which increases with energy transfer according to the second law of thermodynamics.

Oxidation

The loss of electrons from a molecule, often releasing energy.

Reduction

The gain of electrons by a molecule, often storing energy.

Photosystem II (PSII)

The protein complex in the thylakoid membrane that absorbs light energy to initiate photosynthesis.

Proton Motive Force

The potential energy stored as a gradient of protons across the membrane used to synthesize ATP.

Thylakoid

The membranous structure within chloroplasts where light-dependent reactions occur.

Stroma

The fluid matrix of the chloroplast outside the thylakoids where the Calvin cycle takes place.

ADP

A nucleotide that, when combined with inorganic phosphate, forms ATP.

G3P

Glyceraldehyde-3-phosphate, a three-carbon sugar, produced in the Calvin Cycle.

Cellular Respiration

The process of converting glucose and oxygen into ATP, carbon dioxide, and water.

NAD+

A coenzyme involved in redox reactions, acting as an electron carrier.

Mitochondrial Matrix

The space within the inner membrane of the mitochondria where the Krebs Cycle occurs.