Metabolism, Energy, and Enzyme Regulation

Comprehensive vocabulary flashcards covering principles of bioenergetics, thermodynamics, redox chemistry, ATP coupling, and enzyme function and regulation.

Kinetic Energy

The energy of motion, which includes sound, thermal energy, electricity, and electromagnetic radiation.

Potential Energy

The energy stored in position or configuration, which includes gravitational, electrical, chemical energy, and energy stored in chemical bonds.

First Law of Thermodynamics

The principle stating that energy is conserved; it cannot be created or destroyed, but can only be transferred and transformed.

Enthalpy ($H$)

The total energy in a molecule, which includes the potential energy of the molecule (heat content); changes in enthalpy are represented by $\Delta H$.

Exothermic Reaction

A chemical reaction that releases heat energy ($\Delta H < 0$), resulting in products that have less potential energy than the reactants.

Endothermic Reaction

A chemical reaction in which heat energy is taken up ($\Delta H > 0$), resulting in products that have higher potential energy than the reactants.

Entropy ($S$)

The amount of disorder; entropy increases ($\Delta S > 0$) when the products of a chemical reaction become less ordered than the reactant molecules.

Second Law of Thermodynamics

The principle stating that total entropy always increases in isolated systems.

Gibbs Free Energy ($G$)

The amount of energy in a reaction available to do work, which determines whether a reaction is spontaneous or requires added energy to proceed.

Exergonic Reaction

A spontaneous chemical reaction with $\Delta G < 0$ where reactants have higher stored chemical energy than products, releasing energy.

Endergonic Reaction

A non-spontaneous chemical reaction with $\Delta G > 0$ that requires energy input to occur, where reactants have lower stored chemical energy than products.

Energetic Coupling

The pairing of an exergonic reaction with an endergonic reaction, allowing chemical energy released from one reaction to drive another reaction.

Catabolic Pathways

Metabolic pathways that involve the breakdown of molecules and the production of ATP.

Anabolic Pathways

Metabolic pathways that result in the synthesis of larger molecules from smaller components.

Redox Reactions

Reduction-oxidation reactions; chemical reactions that involve the transfer of electrons between molecules or atoms.

Oxidation

The loss of one or more electrons ($e^-$) by an atom or molecule.

Reduction

The gain of one or more electrons ($e^-$) and a hydrogen ion ($H^+$) by an atom or molecule.

Nicotinamide

The nitrogen-containing aromatic ring functional group of nicotinamide adenine dinucleotide (NAD) that accepts electrons and a proton upon reduction.

NADH

An electron carrier that readily donates electrons to other molecules, possesses reducing power, and is involved in cellular respiration.

ATP Hydrolysis

An exergonic reaction that breaks down ATP into ADP and inorganic phosphate ($P_i$), releasing $7.3\,\text{kcal/mol ATP}$ of energy due to clustered negative charges on the linked phosphate groups.

Induced Fit

A conformational shape change an enzyme undergoes when substrates bind to the active site, reorienting the substrates and binding them tighter.

Activation Energy ($E_a$)

The amount of free energy required to reach the intermediate condition or transition state in a chemical reaction.

Catalyst

A substance that lowers the activation energy of a reaction by decreasing the free energy of the transition state, increasing the reaction rate without changing $\Delta G$ or being consumed.

Initiation (Enzyme Catalysis)

The first step of enzyme action where reactants bind to the active site in a specific orientation, forming an enzyme-substrate complex.

Transition State Facilitation

The second step of enzyme action where interactions between the substrate and active site R-groups lower the required activation energy.

Termination (Enzyme Catalysis)

The final step of enzyme action where reaction products have lower affinity for the active site and are released, leaving the enzyme unchanged.

Enzyme Saturation

The condition where all active sites of available enzymes are occupied by substrate, causing the rate of product formation to reach a plateau or maximum speed.

Cofactors

Inorganic ions, such as metal ions $Zn^{2+}$, $Mg^{2+}$, and $Fe^{2+}$, that reversibly interact with enzymes to assist their function.

Coenzymes

Organic molecules that interact with enzymes to help them function.

Prosthetic Groups

Non-amino acid atoms or molecules (such as heme) that are permanently attached to proteins.

Competitive Inhibition

A mechanism of enzyme regulation where a molecule similar in size and shape to the substrate competes directly with the substrate for access to the active site.

Allosteric Regulation

A regulatory mechanism where a molecule alters enzyme shape and activates or deactivates it by binding at a location other than the active site.

Phosphorylation (Enzyme Regulation)

A reversible covalent modification involving the addition of one or more phosphate groups to an enzyme's primary structure to alter its function.

Feedback Inhibition

A metabolic pathway control mechanism that occurs when an abundant end-product molecule allosterically inhibits an early enzyme in the pathway, stopping the reaction sequence.