Energy, Enzymes, and Biological Reactions

Flashcards on Energy, Enzymes, and Biological Reactions based on lecture notes.

Energy

The capacity to do work.

Kinetic energy

Energy of an object in motion, such as a falling rock, electricity, and light.

Potential energy

Stored energy, such as a rock at the top of a hill, chemical energy, gravitational energy, and stored mechanical energy.

Thermodynamics

The study of energy and its transformations.

First law of thermodynamics

States that energy can be transformed or transferred, but cannot be created or destroyed; also known as the principle of conservation of energy.

Second law of thermodynamics

States that the total disorder (entropy) of a system and its surroundings always increases.

Spontaneous reaction

A chemical or physical reaction that will occur without an input of energy.

Enthalpy (H)

The potential energy in a system.

Exothermic reactions

Reactions that release energy; the products have less potential energy than the reactants.

Endothermic reactions

Reactions that absorb energy; the products have more potential energy than the reactants.

Free energy (G)

The portion of a system’s energy that is available to do work.

Equilibrium point

A state of balance between opposing factors pushing a reaction in either direction.

Exergonic reaction

Reaction that releases free energy; ΔG is negative.

Endergonic reaction

Reaction that requires reactants to gain free energy from the surroundings to form products; ΔG is positive.

Metabolic pathway

A series of reactions in which the products of one reaction are used immediately as the reactants for the next reaction in the series.

Catabolic pathway

Pathway in which energy is released by the breakdown of complex molecules to simpler compounds; overall ΔG is negative.

Anabolic pathway

Pathway in which energy is used to build complicated molecules from simpler ones; overall ΔG is positive.

Adenosine triphosphate (ATP)

The nucleotide consisting of ribose, adenine, and three phosphate groups; removal of phosphate groups releases energy.

Hydrolysis of ATP

The breakdown of ATP which results in the formation of adenosine diphosphate (ADP) and a molecule of inorganic phosphate (Pi).

Phosphorylation

The addition of a phosphate group to a molecule.

Energy coupling

Energy from ATP hydrolysis is coupled to an endergonic reaction, with the terminal phosphate group transferred to a reactant molecule.

ATP/ADP cycle

The continual hydrolysis and resynthesis of ATP.

Activation energy (Ea)

The energy required to start a spontaneous reaction.

Catalyst

A chemical agent that accelerates the rate of a reaction without being changed by the reaction.

Enzymes

Proteins that increase the rate of reaction by lowering the activation energy.

Substrate

The reactant that an enzyme acts on.

Active site

A small pocket or groove in the enzyme molecule where the substrate binds.

Cofactor

A nonprotein group that binds to the enzyme for catalytic activity; can be metallic ions or coenzymes.

Coenzymes

Small organic molecules, often derived from vitamins, that act as cofactors.

Enzyme inhibitors

Molecules that bind to an enzyme and decrease its activity.

Competitive inhibition

Inhibition where inhibitors bind to the active site, blocking access for the normal substrate.

Allosteric regulation

Enzyme activity is controlled by the reversible binding of a regulatory molecule to a location on the enzyme outside the active site.

Feedback inhibition/End-product inhibition

Excess accumulation of a product inhibits the enzymatic reaction producing it.

Regulation by chemical modification

Chemical linkage to ions, functional groups, or other molecules that induce changes in the enzyme that increase or decrease its activity.

Ribozymes

RNA molecules that accelerate the rate of certain biological reactions without being changed by the reactions.