Chapter Eight: Energy, Enzymes, and Metabolism

Vocabulary flashcards based on lecture notes regarding biological energy transformations, thermodynamics, ATP cycle, and enzyme function and regulation.

Energy

The capacity to do work, or the capacity to change.

Potential energy

Stored energy existing as chemical bonds, concentration gradients, or charge imbalances (e.g., membrane potential).

Kinetic energy

The energy of movement, such as heat or mechanical energy.

Metabolism

The sum total of all chemical reactions occurring in an organism.

Anabolic reactions (Anabolism)

Metabolic reactions where complex molecules are made from simple molecules; these require energy input and store energy in chemical bonds.

Catabolic reactions (Catabolism)

Metabolic reactions where complex molecules are broken down into simpler ones, resulting in the release of energy.

First Law of Thermodynamics

The principle that energy is neither created nor destroyed; total energy before and after a conversion remains the same.

Second Law of Thermodynamics

The principle that when energy is converted, some of it becomes unavailable to do work, leading to increased disorder.

Enthalpy ($H$)

The total energy in a system, defined by the formula $H = G + TS$, where $G$ is free energy, $T$ is absolute temperature, and $S$ is entropy.

Free Energy ($G$)

The usable energy in a system available to perform work.

Entropy ($S$)

A measure of the disorder or randomness in a system.

Change in Free Energy ($\Delta G$)

The difference in free energy between products and reactants, calculated as $\Delta G = G_{\text{products}} - G_{\text{reactants}}$ or $\Delta G = \Delta H - T\Delta S$.

Exergonic reactions

Reactions that release free energy ($-\Delta G$), typically associated with catabolism and a decrease in complexity.

Endergonic reactions

Reactions that consume free energy ($+\Delta G$), typically associated with anabolism and an increase in complexity or order.

Chemical equilibrium

A state where the forward and reverse reactions are balanced and there is no net change, meaning $\Delta G = 0$.

ATP (adenosine triphosphate)

A nucleotide that captures and transfers free energy; it releases between $-7.3\,kcal/mol$ to $-14\,kcal/mol$ when hydrolyzed.

Enzymes

Proteins that act as catalysts to speed up chemical reactions by lowering the energy barrier without being altered by the reaction.

Activation energy ($E_a$)

The amount of energy required to start a reaction by changing reactants into unstable transition state intermediates.

Substrates

The specific reactant molecules that bind to the active site of an enzyme.

Active site

The specific region of an enzyme where substrates bind and the chemical reaction occurs.

Enzyme-substrate complex ($ES$)

The intermediate formed when an enzyme binds to its substrate, represented by the formula $E + S \rightarrow ES \rightarrow E + P$.

Induced fit

A change in the shape of an enzyme's active site upon substrate binding that improves its catalytic ability.

Prosthetic groups

Non-amino acid groups that are permanently bound to enzymes.

Cofactors

Inorganic ions that some enzymes require in order to function.

Coenzymes

Small carbon-containing molecules that are not permanently bound to enzymes and are used up during the chemical reaction.

Turnover

The number of substrate molecules converted to product per unit of time when an enzyme is fully saturated.

Inhibitor

A molecule that binds to an enzyme and slows down the reaction rate; can be naturally occurring or artificial.

Competitive inhibitors

Molecules that bind noncovalently to the active site of an enzyme, preventing the substrate from binding.

Non-competitive inhibitors

Molecules that bind to a region other than the active site, causing the enzyme to change shape so the active site is unavailable.

Allostery

A regulatory mechanism where an effector binds to a site other than the active site, stabilizing either the active or inactive form of the enzyme.

Feedback inhibition (End-product inhibition)

A process where the final product of a metabolic pathway allosterically inhibits the enzyme that catalyzes the commitment step.

Commitment step

The first reaction in a metabolic pathway, after which the rest of the reactions happen in sequence.

Protein kinase

An enzyme that activates another enzyme by adding a phosphate group (phosphorylation).

Protein phosphatase

An enzyme that removes a phosphate group from an enzyme, often making it inactive again.

Isozymes

Groups of enzymes that catalyze the same reaction but have different amino acid compositions and different physical properties like optimal temperature.