Lecture 11: Energy, Enzymes, and Metabolism

Vocabulary practice flashcards covering bioenergetics, thermodynamics, metabolic pathways, free energy calculations, ATP structure and hydrolysis, enzyme catalysis, and enzyme regulation mechanisms.

Bioenergetics

The study of energy flow through a living system or ecosystem.

Metabolism

The sum of all chemical reactions that take place inside a living organism.

Metabolic Pathways

A series of interconnected chemical reactions in a cell that convert one or more initial reactants into ultimate products.

Anabolic Reactions

Metabolic pathways that require an input of energy to synthesize larger, complex molecules from smaller ones.

Catabolic Reactions

Metabolic pathways that release energy by breaking down large, complex molecules into smaller molecules.

Kinetic Energy

The type of energy associated with objects or particles in motion.

Potential Energy

The energy stored in matter due to its position, arrangement, or chemical bonds that has the potential to perform work.

Gibbs Free Energy ($G$)

The amount of usable energy available to perform work in a system during a chemical reaction.

Gibbs Free Energy Change Equation

The mathematical formula $ΔG = ΔH - T ΔS$, where $ΔH$ represents the change in total enthalpy/system energy, $T$ is absolute temperature in Kelvin, and $ΔS$ is the change in entropy.

Exergonic Reactions

Spontaneous chemical reactions that release energy, yielding products with less free energy than the reactants ($ΔG < 0$).

Endergonic Reactions

Non-spontaneous chemical reactions that require an input of energy, yielding products with more free energy than the reactants ($ΔG > 0$).

Activation Energy

The initial threshold energy required for a chemical reaction to contort reactant molecules into an unstable transition state so bonds can break or form.

Transition State

A high-energy, contorted, and highly unstable state of reactant molecules during a chemical reaction that allows bonds to be broken or created.

First Law of Thermodynamics

The physical law stating that energy cannot be created or destroyed, but can only be transferred or transformed from one form to another.

Second Law of Thermodynamics

The physical law stating that energy transfers are not completely efficient, resulting in unusable energy lost as heat and an increase in overall system entropy (disorder).

ATP (Adenosine Triphosphate)

The primary energy currency molecule of cells, consisting of an adenine base, a ribose sugar, and three bound phosphate groups.

Phosphorylation

The chemical transfer of a terminal phosphate group ($PO_4^{3-}$) from ATP to another molecule, coupling exergonic energy release to drive endergonic processes.

ATP Hydrolysis Energy Yields

The exact energy yield released upon cleavage of phosphate groups, where the first and second phosphate groups yield $7.3\,kcal/mol$ each, and the third yields $3.4\,kcal/mol$.

Sodium-Potassium Pump

An active transport integral membrane protein that uses ATP hydrolysis energy to pump $3\,Na^+$ ions out of the cell and $2\,K^+$ ions into the cell.

Catalysts

Substances, such as enzymes, that speed up chemical reaction rates by lowering the activation energy without being consumed by the reaction.

Induced Fit

A model of enzyme-substrate interaction where a mild conformational shift in the active site shape occurs upon substrate binding to maximize catalytic efficiency.

Competitive Inhibitors

Inhibitor molecules that structurally resemble the substrate and directly compete for binding at the active site of an enzyme.

Noncompetitive Inhibitors

Inhibitors that bind to an enzyme at a site other than the active site, slowing down the overall reaction rate by altering enzyme function.

Allosteric Regulation

Enzyme regulation where allosteric inhibitors modify the active site to decrease substrate binding, while allosteric activators modify the active site to increase substrate affinity.

Cofactors

Inorganic ions, such as $Fe^{2+}$, $Mg^{2+}$, or $Zn^{2+}$ (e.g., $Zn^{2+}$ required by DNA polymerase), that are necessary for proper enzyme function.

Coenzymes

Non-protein organic helper molecules, such as ATP, $NADH^+$, and dietary vitamins, required to assist enzyme activity.

Feedback Inhibition

A metabolic pathway control mechanism where the final end product binds to and inhibits an enzyme operating at an earlier step in the pathway.