Key Concepts in Chemical Reactions and Enzyme Activity

Reactants

The molecules that interact and are transformed during a chemical reaction.

Products

The new molecules formed as a result of a chemical reaction.

Reversible Reaction

A chemical reaction in which the products can react to form the reactants.

Forward Reaction

The reaction proceeding from left to right in a chemical equation.

Reverse Reaction

The reaction proceeding from right to left in a chemical equation.

Gibbs Free Energy (G)

The amount of energy available to do work in a system.

AG

The change in Gibbs free energy during a chemical reaction (free energy of products minus free energy of reactants).

Exergonic Reaction

A spontaneous chemical reaction with a negative AG that releases energy available to do work.

Endergonic Reaction

A non-spontaneous chemical reaction with a positive AG that requires an input of energy.

Spontaneous Reaction

A reaction that releases energy (has a negative AG), not necessarily instantaneous or rapid.

Non-spontaneous Reaction

A reaction that requires a sustained input of energy (has a positive AG).

Enthalpy (H)

The total amount of energy in a system.

Entropy (S)

A measure of the degree of disorder in a system.

Catabolic Reactions

Reactions in which products have less chemical energy (lower enthalpy) and are more disordered (higher entropy) than reactants, resulting in a negative AG.

Anabolic Reactions

Reactions in which products have more chemical energy (higher enthalpy) and are less disordered (lower entropy) than reactants, resulting in a positive AG.

Hydrolysis

A chemical reaction in which a water molecule is split into a proton (H+) and a hydroxyl group (OH-), often breaking down polymers.

Energetic Coupling

A process in which a spontaneous reaction drives a non-spontaneous reaction, requiring a net negative AG for the coupled reactions.

Catalysts

Substances that increase the rate of chemical reactions without themselves being consumed.

Enzymes

Biological catalysts, usually proteins, that accelerate chemical reactions.

Rate of a Chemical Reaction

The amount of product formed (or reactant consumed) per unit of time.

Activation Energy (Ea)

The energy input necessary to reach the transition state in a chemical reaction.

Transition State

A highly unstable intermediate stage in a chemical reaction between reactants and products.

Substrate

The reactant in a chemical reaction catalyzed by an enzyme.

Active Site

The portion of an enzyme that binds the substrate and catalyzes its conversion to the product.

Enzyme-Substrate Complex (ES)

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

Enzyme-Product Complex (EP)

The temporary complex formed when the substrate has been converted to product while still bound to the enzyme.

Inhibitors

Molecules that decrease the activity of enzymes.

Activators

Molecules that increase the activity of enzymes.

Irreversible Inhibitors

Inhibitors that form covalent bonds with enzymes, permanently inactivating them.

Reversible Inhibitors

Inhibitors that form weak bonds with enzymes and easily dissociate.

Allosteric Enzymes

Enzymes whose activity is influenced by molecules binding to a site other than the active site.

Negative Feedback

A regulatory mechanism where the final product of a metabolic pathway inhibits an earlier step in the pathway.

Homeostasis

The active maintenance of stable conditions or steady levels of a substance in an organism.

Cofactor

A substance that associates with an enzyme and plays a key role in its function, often metal ions or small organic molecules.

Saturated fatty acid tails

straight and pack tightly, reducing membrane fluidity

Unsaturated fatty acid tails

have double bonds that introduce kinks, reducing tight packing and increasing membrane fluidity.