Energy, Metabolism, and Enzymes

Energy

The capacity to do work; exists in various forms (kinetic, potential, chemical, thermal, light, electrical).

Kinetic Energy

Energy of motion.

Potential Energy

Stored energy due to position or chemical structure.

Chemical Energy

Potential energy stored in the bonds of chemical compounds.

Thermodynamics

The study of energy transformations.

First Law of Thermodynamics (Law of Conservation of Energy)

Energy cannot be created or destroyed, only transferred or transformed.

Second Law of Thermodynamics

Every energy transfer or transformation increases the entropy (disorder) of the universe.1

Entropy

A measure of disorder or randomness.

Metabolism

The totality of an organism's chemical reactions; manages the material and energy resources of the cell.

Metabolic Pathway

A series of chemical reactions in a cell that builds or breaks down molecules.

Catabolic Pathway

Metabolic pathways that release energy by breaking down complex molecules into simpler compounds.

Anabolic Pathway

Metabolic pathways that consume energy to build complex molecules from simpler ones.

Free Energy (ΔG)

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

Exergonic2 Reaction

A chemical reaction that releases free energy (ΔG<0) and is spontaneous.

Endergonic Reaction

A chemical reaction that absorbs free energy from its surroundings (ΔG>0) and is non-spontaneous.

ATP (Adenosine Triphosphate)

The primary energy currency of the cell; powers most cellular work.

ATP Hydrolysis

The breaking of a phosphate bond in ATP, releasing energy for cellular work.

Energy Coupling

The use of an exergonic process (like ATP hydrolysis) to drive an endergonic one.

Enzyme

A macromolecule (typically a protein) that acts as a biological catalyst, speeding up a specific biochemical reaction without being consumed by the reaction.

Catalyst

A substance that speeds up the rate of a chemical reaction without being used up itself.

Activation Energy (Ea​)

The initial energy input required to start a chemical reaction; enzymes lower this.

Substrate

The reactant that an enzyme acts on.

Active Site

The specific region on an enzyme where the substrate binds.

Enzyme-Substrate Complex

The temporary complex formed when an enzyme binds to its substrate.3

Induced Fit

A change in the shape of an enzyme's active site, induced by the binding of a substrate, that enhances the fit between the enzyme and substrate.

Cofactor

Non-protein helpers for catalytic activity, typically metal ions (e.g., zinc, iron, copper).

Coenzyme

An organic cofactor (e.g., vitamins).

Optimal Temperature/pH

The specific temperature or pH at which an enzyme exhibits maximum activity.

Denaturation

A process in which a protein (or nucleic acid) loses its native shape and function due to the disruption of its molecular structure, often caused by changes in temperature or pH.

Enzyme Inhibition

A molecule that binds to an enzyme and decreases its activity.

Competitive Inhibitor

A substance that reduces the activity of an enzyme by entering the active site in place of the substrate, whose4 structure it mimics.

Noncompetitive Inhibitor

A substance that reduces the activity of an enzyme by binding to a location remote from the active site, changing5 the enzyme's shape so that the active site no longer effectively catalyzes the conversion of substrate to product.

Allosteric Regulation:6 The binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site.

Feedback Inhibition (Negative Feedback)

A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.