Metabolism, Energy, and Enzymes

A complete set of vocabulary practice flashcards covering Chapter 8: Introduction to Metabolism, including bioenergetics, thermodynamics, enzyme kinetics, cofactor interactions, and metabolic regulation.

Metabolism

The totality of an organism's chemical reactions that transforms matter and energy, governed by the laws of thermodynamics.

Catabolism

The metabolic pathway that breaks down larger, complex molecules into smaller ones, releasing the chemical energy stored in their bonds.

Anabolism

The metabolic pathway that consumes energy to build larger, complex molecules from simpler building blocks.

Metabolic Pathway

A sequence of enzymatically catalyzed chemical reactions in a cell, organized as chains or cycles, where each step converts a specific precursor into a subsequent product.

Kinetic Energy

The energy associated with the relative movement of matter, including radiant, mechanical, electrical, and thermal forms.

Potential Energy

Stored energy that matter possesses because of its location or spatial arrangement, such as energy stored in molecular chemical bonds.

Chemical Energy

A form of potential energy stored in chemical bonds that is released when bonds are broken and formed during chemical reactions.

First Law of Thermodynamics

The principle of conservation of energy stating that energy can be transformed and converted from one form to another, but it cannot be created or destroyed.

Second Law of Thermodynamics

The physical law stating that every energy transfer or transformation increases the entropy, or disorder, of a closed system such as the universe.

Entropy

A quantitative measure of randomness or molecular disorder in a system.

Spontaneous Process

A chemical or physical process that occurs without the net addition of external energy, such as passive diffusion down a concentration gradient.

Nonspontaneous Process

A process that requires an input of external energy to proceed, such as active transport against a concentration gradient.

Gibbs Free Energy ($\Delta G$)

A measure of the usable chemical energy in a system; a negative $\Delta G$ indicates that energy is released and the reaction occurs spontaneously.

Reduction Potential ($\Delta E$)

A measure of the tendency of a chemical species to acquire electrons; the more negative the change in potential, the greater the amount of energy released.

Electron Donor

A reduced molecule (termed a reducing agent in chemistry), such as glucose, that donates electrons in a redox metabolic reaction.

Terminal Electron Acceptor

An oxidized molecule (termed an oxidizing agent in chemistry), such as oxygen, that acts as the final recipient of electrons in cellular respiration.

Exergonic Reaction

An energy-yielding chemical reaction (also referred to as exothermic) with a negative $\Delta G$ or $\Delta E$ that is characteristic of catabolic pathways.

Endergonic Reaction

An energy-absorbing chemical reaction (also referred to as endothermic) with a positive $\Delta G$ or $\Delta E$ that powers anabolic pathways.

Energy Coupling

The cellular strategy of using the energy released from an exergonic catabolic process to directly power an endergonic anabolic process.

Adenosine Triphosphate (ATP)

The primary energy-transfer molecule in the cell, composed of an adenine nucleotide with three attached phosphates, releasing approximately $7.3\,\text{kcal/mol}$ upon bond breakdown.

Phosphorylated Intermediate

A recipient molecule that is covalently bonded to a phosphate group transferred from ATP, temporarily raising its free energy and reactivity to drive an anabolic reaction.

Catalyst

A chemical agent that increases the rate of a chemical reaction without being consumed or permanently altered by the process.

Enzyme

A biological macromolecule (predominantly proteins, but also catalytic RNA molecules like ribozymes) that acts as a catalyst by lowering the energy barriers of cellular reactions.

Active Site

The specific catalytic region or groove on an enzyme molecule where the substrate binds to undergo a chemical reaction.

Substrate

The specific target reactant upon which an enzyme acts.

Activation Energy ($E_a$)

The initial investment of energy required to contort reactant molecules so their chemical bonds can break and start a reaction.

Denaturation

A process in which an enzyme loses its native three-dimensional structure and catalytic function due to conditions such as excessive heat or non-optimal pH.

Optimum Temperature

The species-dependent temperature at which an enzyme demonstrates its highest catalytic activity (approximately $37^\circ\text{C}$ for human enzymes).

Optimum pH

The specific pH at which an enzyme functions with maximal efficiency, commonly falling between pH 6 and 8 for most human cellular enzymes.

$$V_{\max}$$

The maximum rate of an enzyme-catalyzed reaction observed when the substrate concentration saturates all available active sites.

Competitive Inhibitor

A regulatory or inhibitory molecule that blocks substrate binding by competing directly for the active site of an enzyme.

Noncompetitive Inhibitor

An inhibitor that binds to an enzyme at a location other than the active site, inducing a conformational change that alters the active site shape and prevents catalysis.

Cofactor

A nonprotein molecule or inorganic metal ion (such as magnesium, manganese, iron, copper, or zinc) required for an enzyme to function properly.

Coenzyme

An organic cofactor, frequently synthesized from vitamins, that aids catalytic function or serves as an electron carrier (e.g., $\text{NAD}^+$, $\text{NADP}^+$, and $\text{FAD}$).

Apoenzyme

The inactive protein component of an enzyme that requires an activating cofactor or coenzyme to form a complete catalytic unit.

Holoenzyme

The complete, catalytically active enzyme complex consisting of the apoenzyme joined with its necessary cofactor or coenzyme.

Water-Soluble Vitamins

Vitamins, such as vitamin B and vitamin C, that dissolve in water, pass readily out of the body in urine, and must be replenished regularly through diet.

Fat-Soluble Vitamins

Vitamins, including vitamins A, D, E, and K, that are absorbed along with dietary lipids and stored in adipose tissues of the body.

Scurvy

A disease caused by vitamin C deficiency that disrupts collagen production, scar tissue maintenance, and iron utilization, leading to bleeding gums, skin blotches, and cell death.

Rickets

A disease resulting from vitamin D deficiency or insufficient ultraviolet light exposure that causes progressive bone weakening.

Pellagra

A nutritional deficiency disease caused by insufficient vitamin B3 (niacin) that leads to extreme sensitivity to sunburn.

Allosteric Regulation

The regulatory mechanism in which a molecule binds to an enzyme at an allosteric site rather than the active site, either stabilizing an active conformation (activation) or an inactive conformation (inhibition).

Cooperativity

A type of allosteric regulation in multisubunit proteins where the binding of a substrate to one subunit stabilizes active conformations in all other subunits, thereby increasing catalytic activity across the complex.

Feedback Inhibition

A control mechanism in which the end product of a metabolic pathway binds allosterically to an early enzyme in the sequence, inhibiting its activity and shutting down the pathway when product levels are sufficient.