Introduction to Metabolism: Energy and Enzymes

Vocabulary practice flashcards covering Chapter 8: Metabolism, thermodynamics, ATP coupling, and enzyme function and regulation.

First Law of Thermodynamics

The law of energy conservation stating that energy can be transferred and transformed, but it cannot be created or destroyed.

Second Law of Thermodynamics

The thermodynamic principle stating that every energy transfer or transformation increases the entropy (disorder) of the universe, with some energy being converted to thermal energy and released as heat.

Kinetic Energy

The energy of motion, which includes heat or thermal energy resulting from the random movement of molecules.

Potential Energy

The energy possessed by matter by virtue of its location or structure.

Chemical Energy

The potential energy available for release in chemical reactions, serving as the most important energy form for living organisms.

Bioenergetics

(1) The overall flow and transformation of energy in an organism. (2) The study of how energy flows through organisms.

Metabolism

The totality of an organism's chemical reactions, representing an emergent property of life that arises from orderly interactions between molecules.

Metabolic Pathway

A series of defined chemical steps in which a specific starting molecule is altered into a product, with each step catalyzed by a specific enzyme.

Catabolic Pathway (Catabolism)

A metabolic pathway that breaks down complex organic matter to harvest energy.

Anabolic Pathway (Anabolism)

A metabolic pathway that uses energy to construct complex macromolecules.

Exergonic Reaction

A chemical reaction that releases energy, in which the reactants have a higher potential energy than the products.

Endergonic Reaction

A chemical reaction that stores energy, in which the products have a higher potential energy than the reactants.

Equilibrium in Metabolism

A state reached by reactions in an isolated system where no work can be performed; the fact that metabolism as a whole is never at equilibrium is a defining feature of life.

ATP (Adenosine Triphosphate)

A molecule composed of adenine, ribose, and three phosphate groups that transports energy in the cell and powers most forms of cellular work.

Phosphorylation

The transfer of a high-energy phosphate group from ATP to another molecule or protein to perform chemical, mechanical, or transport work.

Energy Coupling

The use of an exergonic process (such as ATP hydrolysis, $\Delta G_{\text{ATP}} = -7.3\,\text{kcal/mol}$) to drive an endergonic process (such as glutamic acid conversion to glutamine, $\Delta G_{\text{Glu}} = +3.4\,\text{kcal/mol}$), yielding an overall exergonic net reaction ($\text{Net } \Delta G = -3.9\,\text{kcal/mol}$).

ATP Cycle

The cycle where catabolic reactions supply the energy needed to regenerate ATP from ADP and inorganic phosphate ($\text{P}_{\text{i}}$) to power endergonic cellular work.

Activation Energy ($E_{\text{A}}$)

The initial energy barrier that must be overcome before a chemical reaction can begin, preventing cells from spontaneously breaking down.

Enzyme

A macromolecule (typically a catalytic protein) that speeds up a chemical reaction by lowering its activation energy barrier.

Substrate

The specific reactant molecule that an enzyme binds to and acts upon.

Active Site

The pocket or groove on an enzyme's surface where the substrate interacts and catalysis takes place.

Induced Fit

The conformational changes in the shape of an enzyme or substrate upon binding that adjust the active site into a position to catalyze the reaction.

Competitive Inhibitor

A substance that reduces enzyme activity by directly competing with the substrate and blocking it from entering the active site.

Noncompetitive Inhibitor

A substance that reduces enzyme activity by binding away from the active site at an allosteric site, altering the enzyme's shape.

Allosteric Regulation

The control of an enzyme's activity through the binding of regulatory molecules (activators that stabilize the active form or inhibitors that stabilize the inactive form) at a site other than the active site.

Cooperativity

A form of allosteric activation in multisubunit enzymes where the binding of a substrate molecule to one active site stabilizes the active form across all other subunits.

Feedback Inhibition

A metabolic pathway regulation method where the pathway's end product (such as isoleucine) binds to an allosteric site on an early pathway enzyme (such as threonine deaminase) to halt synthesis when product is abundant.

Glyphosate

A broad-spectrum herbicide developed by Monsanto in 1970 and marketed as Roundup that acts as a competitive inhibitor of EPSP synthase.

EPSP Synthase (EPSPS)

An enzyme that catalyzes the formation of 5-enolpyruvylshikimate-3-phosphate from shikimate-3-phosphate and phosphoenolpyruvate, required for the synthesis of the aromatic amino acids phenylalanine, tyrosine, and tryptophan.

Roundup Ready Crops

Genetically modified crops (corn, soybeans, alfalfa, canola, sugar beets, and cotton) containing an EPSPS enzyme from Agrobacterium tumefaciens that allows fields to be sprayed with glyphosate without harming the crops.