Chapter 3: Energy, Catalysis, and Biosynthesis

Vocabulary flashcards covering key terms and definitions from Essential Cell Biology Chapter 3 on energy, catalysis, thermodynamics, and activated carriers.

Catabolic Pathways

Metabolic pathways that break down food molecules into smaller building blocks and release energy, some of which is lost as heat.

Anabolic Pathways

Metabolic pathways that use the energy harnessed by catabolism to drive the synthesis of the many complex molecules that form the cell.

Oxidation

The removal or loss of electrons from an atom or molecule during a chemical reaction, or the addition/gain of oxygen.

Reduction

The addition or gain of electrons by an atom or molecule during a chemical reaction, or the loss of oxygen.

Activation Energy

The minimum energy barrier that reactant molecules must overcome to initiate a chemical reaction.

Enzyme

A protein catalyst that selectively lowers the activation energy for a specific reaction pathway, accelerating the rate without altering the equilibrium point.

Active Site

The region on an enzyme that binds a substrate molecule and catalyzes its chemical transformation into a product.

Free-Energy Change ($\Delta G$)

A measure of the change in disorder caused by a reaction; a negative value ($\Delta G < 0$) indicates an energetically favorable reaction that can occur spontaneously.

Energetically Unfavorable Reaction

A reaction with a positive free-energy change ($\Delta G > 0$) that increases order in the universe and can proceed only if coupled to an energetically favorable reaction.

Equilibrium Constant ($K$)

The ratio of product concentration to reactant concentrations at chemical equilibrium, expressed as $K = \frac{[AB]}{[A][B]} = \frac{k_{on}}{k_{off}}$.

Random Walk

The path taken by a molecule traversing the cytosol due to frequent thermal collisions with surrounding molecules.

Activated Carrier

A small organic molecule containing high-energy covalent bonds that stores energy in a portable form to power energetically unfavorable cell reactions.

ATP (Adenosine Triphosphate)

The principal activated carrier in cells, storing transferable energy in high-energy phosphoanhydride bonds.

NADPH

An activated carrier of high-energy electrons and hydrogen that serves primarily as a reducing agent in anabolic pathways.

NADH

An activated electron carrier that acts primarily as an intermediate in catabolic pathways that generate ATP.

Acetyl CoA

An activated carrier molecule that holds an acetyl group in a high-energy linkage used in metabolic reactions.

Condensation Reaction

An energetically unfavorable reaction where two molecules are joined covalently with the simultaneous elimination of a water molecule.

Hydrolysis Reaction

An energetically favorable reaction where a covalent bond is cleaved by the addition of a water molecule.

Pyruvate Carboxylase

An enzyme that uses carboxylated biotin to transfer a carboxyl group to pyruvate, forming oxaloacetate.