Campbell Biology in Focus - Chapter 6: An Introduction to Metabolism

Vocabulary terms and definitions covering metabolic pathways, laws of thermodynamics, free energy, ATP function, and enzyme regulation based on Chapter 6 lecture notes.

Metabolism

The totality of an organism’s chemical reactions, emerging from orderly interactions between molecules.

Metabolic pathway

A process that begins with a specific molecule and ends with a product, where each step is catalyzed by a specific enzyme.

Catabolic pathways

Metabolic pathways that release energy by breaking down complex molecules into simpler compounds, such as cellular respiration.

Anabolic pathways

Also called biosynthetic pathways; they consume energy to build complex molecules from simpler ones, such as protein synthesis from amino acids.

Bioenergetics

The study of how energy flows through living organisms.

Energy

The capacity to cause change.

Work

The movement of matter against opposing forces, such as gravity and friction.

Kinetic energy

Energy associated with the motion of objects.

Thermal energy

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

Heat

Thermal energy in transfer from one object to another.

Potential energy

Energy that matter possesses because of its location or structure.

Chemical energy

A type of potential energy available for release in a chemical reaction.

Thermodynamics

The study of energy transformations that occur in a collection of matter.

First law of thermodynamics

Also called the principle of conservation of energy; it states that the energy of the universe is constant and can be transferred or transformed, but not created or destroyed.

Second law of thermodynamics

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

Entropy

A measure of molecular disorder or how dispersed energy is in a system.

Spontaneous processes

Processes that occur without energy input and must increase the entropy of the universe.

Free energy

Represented by the symbol $G$; the portion of a system’s energy that can do work when temperature and pressure are uniform throughout.

Exergonic reaction

A reaction that proceeds with a net release of free energy where $\text{delta G}$ is negative and the process is spontaneous.

Endergonic reaction

A reaction that absorbs free energy from its surroundings where $\text{delta G}$ is positive and the process is nonspontaneous.

Energy coupling

The use of an exergonic process to drive an endergonic one, most of which is mediated by A T P in cells.

A T P (adenosine triphosphate)

A molecule composed of ribose, adenine, and three phosphate groups used for energy coupling and R N A synthesis.

Phosphorylation

The transfer of a phosphate group from A T P to another molecule, such as a reactant.

Phosphorylated intermediate

The recipient molecule with the phosphate group covalently bonded to it, which is more reactive than the original unphosphorylated molecule.

Catalyst

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

Enzyme

A macromolecule (typically a protein) that acts as a catalyst by lowering the activation energy barrier.

Activation energy

Represented as $E_A$; the energy required to start a reaction by breaking bonds in the reactant molecules.

Substrate

The reactant molecule on which an enzyme acts.

Enzyme-substrate complex

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

Active site

The specific region of an enzyme that binds the substrate and where catalysis occurs.

Induced fit

The change in shape of the active site of an enzyme so that it binds more snugly to the substrate, caused by entry of the substrate.

Cofactors

Nonprotein molecules that help enzymes carry out processes; may be inorganic (metals) or organic.

Coenzyme

An organic cofactor, such as a vitamin.

Competitive inhibitors

Molecules that reduce enzyme productivity by blocking substrates from entering active sites.

Noncompetitive inhibitors

Molecules that bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective.

Allosteric regulation

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

Cooperativity

A type of allosteric activation where the binding of one substrate molecule to one active site locks all other subunits into the active shape.

Feedback inhibition

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