Energy, Reactions, and Enzymes Sep 3

Vocabulary flashcards covering energy, thermodynamics, and enzymes based on the lecture notes.

Ligand binding

Binding of a ligand to a protein causes a conformational change and can alter the protein’s affinity for other ligands; this mechanism underlies many physiological processes.

Conformational change

A change in the three‑dimensional shape of a protein when a ligand binds, enabling or modulating its function.

Affinity

The strength of the interaction between a protein and its ligand; binding can affect affinity for additional ligands.

First Law of Thermodynamics

Energy cannot be created or destroyed; it is transformed from one form to another, and all reactions involve energy changes.

Second Law of Thermodynamics

All systems tend toward greater disorder over time; the law of entropy.

Entropy

A measure of disorder in a system; entropy tends to increase as processes proceed toward equilibrium.

Gibbs Free Energy (ΔG)

ΔG = ΔH − TΔS; indicates usable energy to do work; ΔH is enthalpy, ΔS is entropy, T is temperature.

Endergonic reactions

Reactions that require input of energy; products have more free energy than reactants (example: photosynthesis).

Exergonic reactions

Reactions that release energy; products have less free energy than reactants (example: breakdown of glucose).

Coupled reactions

Process where an exergonic reaction provides energy to drive an endergonic reaction; overall energy decreases.

ATP (adenosine triphosphate)

Cellular energy currency; hydrolysis to ADP and Pi releases energy for cellular work; energy stored in phosphate bonds.

ADP (adenosine diphosphate)

Product of ATP hydrolysis; can be rephosphorylated to form ATP.

Phosphorylation

Addition of a phosphate group to a molecule; often driven by ATP; helps couple energy transfer.

Energy coupling

Using energy released by exergonic reactions to drive endergonic ones; energy is stored in ATP for later use.

Activation energy

The energy required to reach the transition state so a reaction can proceed; many molecules lack this energy naturally.

Transition state

A high‑energy, unstable arrangement of atoms at the top of the reaction barrier; the point along the path with the highest energy.

Enzyme

Biological catalyst; increases reaction rate, is not consumed, does not alter the reaction’s overall outcome, and lowers the activation energy.

Active site

A pocket on the enzyme’s surface where the substrate binds; the enzyme’s 3D shape and pockets determine specificity.

Catabolism

Metabolic pathways that break down molecules to release energy (exergonic processes).

ATP hydrolysis

The reaction ATP + H2O → ADP + Pi; releases energy (about 30.5 kJ/mol) to power cellular work.