Thermodynamics & Metabolic Basics

A comprehensive set of vocabulary flashcards covering thermodynamics, redox chemistry, enzymes, and metabolic regulation concepts from the lecture.

Gibbs Free Energy (ΔG)

The energy in a system available to do work; calculated as ΔG = ΔH – TΔS.

Enthalpy (ΔH)

The heat content or total bond energy of a system.

Entropy (ΔS)

A measure of disorder or randomness in a system.

Exergonic Reaction

A chemical reaction with ΔG < 0 that releases free energy.

Endergonic Reaction

A chemical reaction with ΔG > 0 that requires an input of free energy.

Exothermic vs. Exergonic

Exothermic releases heat (chemistry), while exergonic releases free energy and has ΔG < 0 (biology).

Endothermic vs. Endergonic

Endothermic absorbs heat; endergonic absorbs free energy (ΔG > 0).

Energetic Coupling

Using energy released by an exergonic reaction to drive an endergonic reaction.

Oxidation

Loss of electrons from a molecule (LEO).

Reduction

Gain of electrons by a molecule (GER).

Redox Reaction

A paired oxidation-reduction process where electrons move from donor to acceptor.

Oxidizing Agent

The substance that accepts electrons and becomes reduced.

Reducing Agent

The substance that donates electrons and becomes oxidized.

NAD⁺

Oxidized form of nicotinamide adenine dinucleotide; ready to accept electrons.

NADH

Reduced, electron-loaded form of NAD⁺; carries electrons and an H⁺.

FAD

Oxidized flavin adenine dinucleotide, an electron carrier.

FADH₂

Reduced form of FAD that carries two electrons and two protons.

Electron Carrier

Molecule like NADH or FADH₂ that transports electrons between reactions.

Phosphorylation

Addition of a phosphate group, often activating a molecule.

Dephosphorylation

Removal of a phosphate group, often deactivating a molecule.

ATP (Adenosine Triphosphate)

Primary energy currency of the cell containing three phosphate groups.

ATP Hydrolysis

Exergonic cleavage of ATP to ADP + Pi, releasing ~7.3 kcal mol⁻¹.

ADP (Adenosine Diphosphate)

Two-phosphate form produced after ATP hydrolysis; can be re-phosphorylated.

Inorganic Phosphate (Pi)

Free phosphate group released during ATP hydrolysis.

Activation Energy (Ea)

Minimum energy required to initiate a chemical reaction.

Catalyst

Substance that speeds a reaction without being consumed.

Enzyme

Protein catalyst that lowers activation energy of biological reactions.

Substrate

Reactant molecule that binds to an enzyme’s active site.

Active Site

Region on an enzyme where the substrate binds and reacts.

Transition State

High-energy, unstable arrangement of atoms during a reaction.

Saturation Kinetics

Plateau in reaction rate when all enzyme active sites are occupied.

Competitive Inhibition

Regulation where an inhibitor occupies the active site, blocking substrate binding.

Allosteric Regulation

Regulation by a molecule binding to a site other than the active site, altering enzyme activity.

Feedback Inhibition

Pathway control where the end product inhibits an early enzyme in the pathway.

Covalent Modification

Regulation via covalent changes to an enzyme, e.g., phosphorylation.

Metabolism

The collective set of chemical reactions in a cell, including catabolism and anabolism.

Glycolysis

Metabolic pathway that begins glucose breakdown and nets ATP and NADH.

Oxidative Phosphorylation

ATP production driven by redox reactions and a proton gradient in mitochondria.

LEO the Lion Says GER

Mnemonic: Loss of Electrons = Oxidation; Gain of Electrons = Reduction.

Activation Energy Barrier

Energy hill lowered by enzymes, allowing reactions to proceed faster.