Bioenergetics, Catalysis, and Biochemistry

Practice vocabulary flashcards covering bioenergetics, thermodynamics, free energy, enzymes, and cellular metabolism from Chapters 3 & 4.

Bioenergetics

The study of energy transformations in living organisms.

Kinetic Energy

The energy possessed by an object or system due to its motion.

Potential Energy

The energy stored in an object or system due to its position.

Work

The energy released during an energy transformation that is used to move matter or drive processes.

First Law of Thermodynamics

The principle stating that energy cannot be created or destroyed, only transformed from one form to another.

Second Law of Thermodynamics

The principle stating that energy events tend to proceed downhill from higher to lower energy states, with every energy transformation causing an increase in total entropy in the universe.

Entropy

A measure of the energy in a system that is unavailable to do work, representing the randomness or disorder of the system ($S$).

Enthalpy

The total energy of a thermodynamic system ($H$), related to free energy and entropy by the equation $H = G + TS$.

Gibbs Free Energy

The energy of a system or molecule available to do useful work at constant temperature ($G$), defined by $G = H - TS$.

Free-Energy Change ($\Delta G$)

The difference in free energy between products and reactants ($G_{\text{products}} - G_{\text{reactants}}$), measuring the disorder caused by a reaction and its distance from equilibrium.

Standard Free-Energy Change ($\Delta G^\circ$)

The gain or loss of free energy in kilojoules per mole when one mole of reactant is converted to one mole of product under standard conditions ($1\,\text{M}$ concentration, $\text{pH } 7.0$).

Exergonic Reaction

A spontaneous chemical reaction that releases energy as it proceeds, characterized by a negative free-energy change ($\Delta G < 0$).

Endergonic Reaction

A non-spontaneous chemical reaction that requires an input of energy to proceed, characterized by a positive free-energy change ($\Delta G > 0$).

Chemical Equilibrium

The state in a reversible reaction where the forward and backward reactions occur at equal rates, resulting in no net change in reactant and product ratio, and $\Delta G = 0$.

Equilibrium Constant ($K$)

The ratio of concentrations $[X]/[Y]$ reached at chemical equilibrium, directly proportional to standard free-energy change at $37\,^\circ\text{C}$ by the equation $\Delta G^\circ = -5.94 \log_{10}(K)$.

Activation Energy ($E_A$)

The extra energy needed to start a chemical reaction by forcing reactants into a transition state.

Catalyst

A substance that accelerates a chemical reaction by lowering its activation energy without being consumed or altered by the reaction.

Enzyme

A biological protein catalyst that increases the rate of specific cellular reactions without changing the reaction's $\Delta G^\circ$ or equilibrium point.

Ribozyme

An RNA molecule capable of folding into structures that catalyze specific chemical reactions.

Metabolism

The complete collection of biochemical reactions occurring within a living cell, organized into interconnected metabolic pathways.

Catabolic Pathways

Metabolic reactions that break down complex food molecules into smaller building blocks and useful energy, releasing heat in the process.

Anabolic Pathways

Metabolic reactions that use energy and building blocks generated by catabolism to synthesize complex molecules that form the cell.

Activated Carrier

A small organic molecule that stores energy in easily transferable high-energy chemical bonds or reactive electrons (e.g., ATP, NADPH).

Hydrolysis

A reaction in which a covalent bond is split by adding a water molecule ($\text{H}_2\text{O}$).

Oxidation

The loss of electrons (or a pair of electrons) from an atom or molecule during a chemical reaction.

Reduction

The gain of electrons (or a pair of electrons) by an atom or molecule during a chemical reaction.

NADH

An activated electron carrier that primarily functions as an oxidizing agent for catabolic reactions ($\text{NAD}^+$ in its oxidized state).

NADPH

An activated electron carrier that primarily functions as a reducing agent for anabolic reactions ($\text{NADP}^+$ in its oxidized state).

Coupled Reaction

A process where an energetically unfavorable reaction ($\Delta G > 0$) is linked to an energetically favorable reaction ($\Delta G < 0$) via shared intermediates, making the overall combined $\Delta G < 0$.