Chapter 8: Metabolism, Energy, and Enzymes

Vocabulary practice flashcards covering cellular metabolism, bioenergetics, thermodynamic laws, free energy, ATP structure and hydrolysis, enzyme function, and mechanisms of inhibition.

Metabolic Pathway

A series of sequential chemical reactions, each catalyzed by a specific enzyme, that begins with a specific starting molecule and results in a product.

Catabolic Pathways

Metabolic pathways that release energy by breaking down complex molecules into simpler compounds, such as cellular respiration breaking down glucose in the presence of oxygen.

Anabolic Pathways

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

Bioenergetics

The study of how organisms manage their energy resources.

Kinetic Energy

Energy associated with the relative motion of objects.

Heat (Thermal Energy)

Kinetic energy associated with the random movement of atoms or molecules.

Potential Energy

Energy that matter possesses because of its location or structure.

Chemical Energy

The potential energy available for release in a chemical reaction.

First Law of Thermodynamics

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

Second Law of Thermodynamics

The principle stating that every energy transformation or transfer increases the entropy (randomness) of the universe.

Free Energy ($G$)

The portion of a system's energy that is available to perform work when temperature and pressure are uniform throughout the system.

Exergonic Reaction

A spontaneous chemical reaction that proceeds with a net release of free energy, resulting in a negative change in free energy (\Δ G < 0).

Endergonic Reaction

A non-spontaneous chemical reaction that absorbs free energy from its surroundings, resulting in a positive change in free energy (\Δ G > 0).

Energy Coupling

The use of an exergonic process to drive an endergonic one, mediated primarily in cells by ATP to ensure the overall net reaction is exergonic.

Adenosine Triphosphate (ATP)

An energy-mediating molecule composed of the nitrogenous base adenine, the pentose sugar ribose, and a chain of three phosphate groups.

Transport Work (Cellular)

A form of cellular work where ATP phosphorylates transport proteins, causing conformational changes that pump solutes across a cell membrane.

Mechanical Work (Cellular)

A form of cellular work where ATP binds noncovalently to motor proteins and is hydrolyzed, moving the motor protein and its attached vesicle along cytoskeletal tracks.

Catalyst

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

Enzyme

A catalytic protein that accelerates a biochemical reaction by lowering the activation energy barrier without affecting the change in free energy (\Δ G).

Activation Energy ($E_A$)

The initial free energy required to break bonds and start a chemical reaction, often supplied as heat from the surroundings.

Substrate

The specific reactant molecule that an enzyme binds to and acts upon.

Active Site

The specific region or pocket on an enzyme where the substrate binds and catalysis takes place.

Induced Fit

The tightening of an enzyme's active site around the substrate following initial binding, bringing chemical groups into optimal positions to catalyze the reaction.

Cofactor

A non-protein helper required for proper enzymatic activity, specifically inorganic ions such as $Mg^{2+}$.

Coenzyme

An organic non-protein molecule required by certain enzymes to facilitate catalytic activity, such as vitamins.

Competitive Inhibitor

A substance that reduces enzyme productivity by mimicking the substrate and binding directly to the active site, blocking substrate entry.

Noncompetitive Inhibitor

A substance that impedes enzymatic reactions by binding to an alternate site on the enzyme, inducing a shape change that renders the active site less effective.