Energy, Enzymes, and Metabolism

Practice vocabulary flashcards covering the thermodynamic principles, enzyme mechanisms, and metabolic regulation from Chapter 8.

Metabolism

The sum total of all chemical reactions occurring in a biological system at a given time.

Energy

The capacity to do work, or the capacity for change.

Potential energy

Energy stored as chemical bonds, a concentration gradient, or a charge imbalance.

Kinetic energy

The energy of movement.

Anabolic reactions

Metabolic reactions in which complex molecules are made from simple molecules, requiring an input of energy.

Catabolic reactions

Metabolic reactions in which complex molecules are broken down into simpler ones, releasing energy.

First law of thermodynamics

The principle stating that energy is neither created nor destroyed, meaning the total energy before and after conversion remains identical.

Second law of thermodynamics

The principle stating that when energy is converted from one form to another, some of that energy becomes unavailable to do work, and disorder tends to increase.

Entropy ($S$)

A quantitative measure of the disorder in a system.

Enthalpy ($H$)

The total energy in a biological system, defined by the formula $H = G + TS$.

Free energy ($G$)

The usable energy in a system that is available to do work.

Exergonic reaction

A reaction that releases free energy ($-\Delta G$), in which catabolism breaks down an ordered reactant to decrease complexity and increase disorder.

Endergonic reaction

A reaction that consumes free energy ($+\Delta G$), in which anabolism synthesizes a highly ordered product from smaller reactants to increase complexity.

Chemical equilibrium

A state of balance between forward and reverse reactions where there is no net change and $\Delta G = 0$.

ATP (Adenosine triphosphate)

A biomolecule composed of adenine, ribose, and three phosphate groups that captures and transfers free energy within cells.

Catalyst

Any substance that increases the rate of a chemical reaction without being permanently altered by the reaction.

Activation energy ($E_a$)

The initial energy barrier required to start a reaction by bringing reactants into a reactive mode called the transition state.

Transition-state intermediate

An unstable, high-free-energy form of the reactants generated during the transition state of a reaction.

Substrate

A specific reactant molecule that binds to the active site of an enzyme.

Active site

The specific three-dimensional region on an enzyme where substrate molecules bind and catalysis takes place.

Enzyme–substrate complex ($ES$)

An intermediate complex held together by hydrogen bonds, electrical attraction, or covalent bonds during an enzymatic reaction.

Induced fit

The structural change in enzyme conformation upon binding a substrate, altering the shape of the active site to facilitate catalysis.

Ribozymes

RNA molecules that function as biological catalysts, such as the RNA that catalyzes peptide bond formation between amino acids.

Prosthetic groups

Non-amino acid molecular groups that are permanently bound to enzymes to assist their function.

Inorganic cofactors

Inorganic metal ions or atoms permanently bound to an enzyme that assist in catalytic reactions.

Coenzymes

Small, carbon-containing nonprotein molecules that temporarily bind to an enzyme to participate in catalysis.

Turnover number

The number of substrate molecules converted to product per unit of time when an enzyme is fully saturated, measuring enzyme efficiency.

Systems biology

A scientific discipline that uses computer algorithms to model complex, interconnected networks of metabolic pathways.

Irreversible inhibition

A form of enzyme inhibition where an inhibitor permanently inactivates an enzyme by forming covalent bonds with side chains in the active site.

Competitive inhibitor

A reversible inhibitor that noncovalently binds to the active site of an enzyme, competing directly with the natural substrate.

Uncompetitive inhibitor

An inhibitor that binds selectively to the enzyme–substrate complex, preventing the release of products.

Noncompetitive inhibitor

An inhibitor that binds to an enzyme at a site other than the active site, inducing a conformational change that alters active site functionality.

Allosteric regulation

The regulation of an enzyme where an effector molecule binds at a regulatory site distinct from the active site, alternating the enzyme between active and inactive forms.

Commitment step

The first reaction in a metabolic pathway, after which the subsequent enzymatic steps proceed in sequence.

Feedback inhibition

A pathway regulation mechanism in which the end product acts as a noncompetitive inhibitor of the first enzyme, shutting down the entire pathway.