chapter 8: An Introduction to Metabolism

Vocabulary flashcards covering the key concepts of metabolism, thermodynamics, energy transformations, ATP, and enzyme function as presented in Chapter 8.

Metabolism

The totality of an organism’s chemical reactions; an emergent property of life arising from orderly interactions between molecules.

Metabolic pathway

A series of chemical reactions 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

Metabolic pathways that consume energy to build complex molecules from simpler ones, such as the synthesis of protein from amino acids.

Bioenergetics

The study of how organisms manage their energy resources.

Kinetic energy

Energy associated with motion.

Heat (thermal energy)

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

Potential energy

The energy that matter possesses because of its location or structure.

Chemical energy

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

Thermodynamics

The study of energy transformations.

Isolated system

A system that is isolated from its surroundings, such as liquid in a thermos.

Open system

A system in which energy and matter can be transferred between the system and its surroundings; organisms are open systems.

First Law of Thermodynamics

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

Second Law of Thermodynamics

States that every energy transfer or transformation increases the entropy (disorder) of the universe.

Entropy

A measure of disorder or randomness within a system.

Spontaneous processes

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

Free energy ($\Delta G$)

Energy that can do work when temperature and pressure are uniform, as in a living cell.

$$\Delta G = \Delta H - T\Delta S$$

The equation for the change in free energy, where $\Delta H$ is the change in enthalpy, $T$ is the temperature in Kelvin, and $\Delta S$ is the change in entropy.

Exergonic reaction

A reaction that proceeds with a net release of free energy and is spontaneous ($\Delta G < 0$).

Endergonic reaction

A reaction that absorbs free energy from its surroundings and is nonspontaneous ($\Delta G > 0$).

Energy coupling

The use of an exergonic process to drive an endergonic one, most often mediated by ATP in cells.

ATP (adenosine triphosphate)

The cell’s energy shuttle, composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups.

Phosphorylation

The transfer of a phosphate group from ATP to another molecule, such as a reactant.

Phosphorylated intermediate

The recipient molecule that receives a phosphate group during phosphorylation.

Catalyst

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

Enzyme

A catalytic protein that speeds up metabolic reactions by lowering energy barriers.

Activation energy ($E_A$)

The initial energy needed to start a chemical reaction, also known as the free energy of activation.

Substrate

The specific reactant that an enzyme acts on.

Enzyme-substrate complex

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

Active site

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

Induced fit

The change in shape of the active site of an enzyme so that it binds more snugly to the substrate, enhancing its ability to catalyze the reaction.

Cofactors

Nonprotein enzyme helpers that may be inorganic (metal ions) or organic.

Coenzyme

An organic cofactor, such as a vitamin.

Competitive inhibitors

Substances that reduce the productivity of enzymes by blocking substrates from entering active sites.

Noncompetitive inhibitors

Substances that bind to a part of an enzyme other than the active site, causing the enzyme to change shape and making the active site less effective.

Allosteric regulation

The term used to describe any case in which a protein's function at one site is affected by the binding of a regulatory molecule to a separate site.

Cooperativity

A form of allosteric regulation where the binding of one substrate molecule to an active site primes the enzyme to act on additional substrate molecules more readily.

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.