Energy and Enzymes Lecture 4–5

Vocabulary flashcards covering essential terms from the Energy and Enzymes lecture, including principles of thermodynamics, metabolism, ATP, redox reactions, and enzyme structure and regulation.

Energy

The capacity to do work; expressed in kilojoules (kJ) or kilocalories (kcal).

Work

Any change in the state or motion of matter caused by energy.

Potential Energy

Energy stored because of position or state (e.g., drawn bow, chemical bonds).

Kinetic Energy

Energy of motion that performs work (e.g., moving arrow, heat).

Chemical Energy

Potential energy stored in chemical bonds, such as those in food molecules.

Metabolism

All chemical reactions occurring in an organism.

Metabolic Pathway

Series of enzyme-controlled reactions in which the product of one reaction is the substrate for the next.

Catabolic Pathway

Metabolic pathway that releases energy by breaking complex molecules into simpler ones.

Anabolic Pathway

Metabolic pathway that consumes energy to build complex molecules from simpler ones.

Thermodynamics

The study of energy and its transformations.

First Law of Thermodynamics

Energy cannot be created or destroyed, only transformed or transferred.

Second Law of Thermodynamics

Every energy conversion increases entropy; usable energy decreases as heat is dispersed.

Entropy (S)

A measure of disorder or randomness; higher for dispersed heat, lower for organized energy.

Heat

Kinetic energy of randomly moving particles, often produced during energy conversions.

Enthalpy (H)

Total potential (bond) energy of a system.

Free Energy (G)

Portion of a system’s energy that can perform work under biochemical conditions.

ΔG

Change in free energy; calculated as ΔG = ΔH − TΔS.

Exergonic Reaction

Spontaneous reaction that releases free energy (ΔG < 0).

Endergonic Reaction

Reaction that requires an input of free energy (ΔG > 0).

Activation Energy (EA)

Energy required to break existing bonds and initiate a chemical reaction.

Coupled Reactions

Pairing of an exergonic reaction with an endergonic reaction so that the overall process is energetically favorable.

ATP (Adenosine Triphosphate

Primary energy currency of the cell; releases energy when hydrolyzed to ADP + Pi.

ADP (Adenosine Diphosphate)

Product of ATP hydrolysis; can be phosphorylated to regenerate ATP.

Phosphorylation

Transfer of a phosphate group, often coupling ATP hydrolysis to endergonic processes.

ATP Cycle

Continuous formation and hydrolysis of ATP, linking catabolic and anabolic reactions.

Redox Reaction

Reaction involving transfer of electrons; includes oxidation and reduction.

Oxidation

Loss of electrons (or hydrogen) from a substance.

Reduction

Gain of electrons (or hydrogen) by a substance.

Electron Carrier

Molecule that transfers electrons (often as H atoms) in redox reactions.

NAD⁺ (Nicotinamide Adenine Dinucleotide)

Electron carrier reduced to NADH during cellular respiration.

NADH

Reduced form of NAD⁺; donates electrons to the electron transport chain.

NADP⁺

Electron carrier reduced to NADPH; mainly used in photosynthesis.

NADPH

Reduced form of NADP⁺; provides reducing power for biosynthetic reactions.

FAD (Flavin Adenine Dinucleotide)

Electron carrier reduced to FADH₂ in metabolic pathways.

FADH₂

Reduced form of FAD; donates electrons during cellular respiration.

Cytochrome

Iron-containing protein that transfers electrons in electron transport chains.

Enzyme

Biological catalyst, usually a protein, that speeds up reactions without being consumed.

Apoenzyme

Protein portion of an enzyme, inactive without its cofactor.

Cofactor

Non-protein helper (metal ion or organic molecule) required for enzyme activity.

Coenzyme

Organic cofactor (often derived from vitamins) that temporarily carries electrons or chemical groups.

Active Site

Region on an enzyme where the substrate binds and catalysis occurs.

Substrate

Reactant molecule on which an enzyme acts.

Enzyme-Substrate Complex

Temporary association between enzyme and substrate during catalysis.

Lock and Key Model

Early model proposing enzymes have rigid active sites that fit substrates exactly.

Induced Fit Model

Current model where substrate binding induces a conformational change in the enzyme, enhancing catalysis.

Optimal Temperature

Temperature at which an enzyme’s catalytic activity is highest.

Optimal pH

pH value at which an enzyme’s activity is maximal.

Competitive Inhibition

Reversible inhibition where an inhibitor competes with the substrate for the active site.

Noncompetitive Inhibition

Reversible inhibition where an inhibitor binds to an allosteric site, altering the active site.

Allosteric Site

Site on an enzyme other than the active site where regulators bind, affecting activity.

Feedback Inhibition

Regulatory mechanism where the end product of a pathway inhibits an earlier enzyme.

Irreversible Inhibition

Permanent inactivation of an enzyme by covalent binding of an inhibitor.

Multienzyme Complex

Assembly of several enzymes that catalyze sequential steps of a pathway, passing intermediates directly.

Gene Control (of Enzymes)

Regulation of enzyme concentrations through switching genes on or off.

Concentration Gradient

Difference in solute concentration across a space; represents potential energy for diffusion.

Saturation (Enzyme)

State in which increasing substrate concentration no longer increases enzyme reaction rate.

Catalase

Enzyme that rapidly decomposes hydrogen peroxide; exhibits one of the highest catalytic rates known.

Phosphoanhydride Bond

High-energy bond between phosphate groups in ATP whose hydrolysis releases energy.

Hydrolysis of ATP

Reaction ATP + H₂O → ADP + Pi + energy (ΔG ≈ −32 kJ/mol).

Conformational Change

Alteration in protein shape, often induced by ligand binding, crucial for enzyme function.

Temperature Denaturation

Loss of enzyme structure and activity due to excessive heat breaking intramolecular bonds.

pH Denaturation

Loss of enzyme activity as extreme pH disrupts ionic and hydrogen bonds stabilizing protein structure.

Electron Transport Chain

Series of redox carriers that transfer electrons, releasing energy to form ATP.

Phosphate Group (Pi)

Inorganic phosphate released upon ATP hydrolysis or added during phosphorylation reactions.