Chapter 8 Metabolism and Enzyme Regulation

Flashcards covering metabolism, thermodynamics, ATP energy coupling, enzyme function and structure, inhibition, and mechanisms of metabolic regulation.

Metabolism

The totality of an organism's chemical reactions, which follows the laws of thermodynamics.

Metabolic Pathway

A series of reactions that begins with a specific molecule and ends with a product, where each step is catalyzed by a specific enzyme.

Catabolic Pathways

Metabolic pathways that release energy by breaking down complex molecules into simpler ones, such as cellular respiration and the breakdown of glucose.

Anabolic Pathways

Metabolic pathways that consume energy to build complex molecules from simpler ones, such as the synthesis of proteins from amino acids.

First Law of Thermodynamics

The principle stating that the energy of the universe is constant; energy can be transferred and transformed, but not created or destroyed. Also called the law of conservation of energy.

Second Law of Thermodynamics

The principle stating that the entropy of the universe is increasing, and the entropy of a closed system is greater than or equal to zero.

Entropy ($S$)

A measure of disorder that serves as a primary driving force for all physical properties. For spontaneous reactions, the entropy of the universe always increases.

Free Energy ($G$)

The energy in a living system that can do work; a lower $\text{AG}$ represents a more stable state.

Free Energy Change Equation

$\Delta G = \Delta H - T\Delta S$, where $\Delta H$ is enthalpy (heat), $\Delta S$ is entropy, and $T$ is temperature in Kelvin.

Exergonic Reaction

A reaction characterized by a negative $\Delta G$, which is favorable, spontaneous, and releases energy.

Endergonic Reaction

A reaction characterized by a positive $\Delta G$, which is unfavorable, nonspontaneous, and requires energy input.

Energy Coupling

The use of an exergonic process to drive an endergonic one, turning an unfavorable reaction into a favorable one.

ATP (Adenosine Triphosphate)

The main energy currency molecule in cells, composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups.

Phosphorylation

The process by which ATP drives endergonic reactions by transferring a phosphate group to another molecule.

Phosphorylated Intermediate

The recipient molecule (either a substrate or an enzyme) that receives a phosphate group during phosphorylation, which changes its activity.

Catalyst

A chemical agent that speeds up a reaction without being consumed by the reaction.

Enzyme

A catalytic protein that speeds up chemical reactions by lowering the activation energy ($E_A$) barrier without changing the free energy change ($\Delta G$).

Activation Energy ($E_A$)

The minimum amount of energy required for a chemical reaction to occur.

Substrate

The specific reactant or ligand that binds to a specific enzyme.

Active Site

The specific region on an enzyme where the substrate binds to catalyze a reaction.

Induced Fit

The closing of the enzyme's active site around the substrate to facilitate catalysis.

Cofactors

Nonprotein enzyme helpers that assist in enzyme activity, which can be inorganic (such as metal in ionic form) or organic.

Coenzyme

An organic cofactor, such as many vitamins, that assists enzyme function.

Competitive Inhibitors

Inhibitors that bind directly to the active site of an enzyme and block the substrate from binding.

Noncompetitive Inhibitors

Inhibitors that bind away from the active site, altering the shape of the binding site and decreasing enzyme activity.

Allosteric Regulation

A regulatory mechanism where a molecule binds to a protein at one site and affects the protein's function at another site, either inhibiting or stimulating enzyme activity.

Cooperativity

A form of allosteric regulation where one substrate molecule binding to an active site primes the enzyme to bind additional substrates tighter or weaker.

Feedback Inhibition

A regulatory mechanism in which the end product of a metabolic pathway inhibits an enzyme earlier in the pathway to prevent wasting chemical resources.

Enzyme Localization

The compartmentalization of enzymes within specific cellular locations to control metabolic pathways, such as locating respiration enzymes strictly in mitochondria.