Bioenergetics, Enzymes, Cellular Respiration, and Photosynthesis

Comprehensive practice flashcards covering thermodynamics, enzyme kinetics, cellular respiration pathways, and photosynthesis based on student lecture notes and slides.

Kinetic Energy

The energy of motion possessed by moving objects, particles, or waves; includes mechanical, electrical, thermal, radiant (electromagnetic), and sound energy.

Potential Energy

Stored energy or energy of position waiting to be released and converted into kinetic energy; includes chemical energy stored in molecular bonds, gravitational energy, nuclear energy, and elastic energy.

First Law of Thermodynamics

The Law of Conservation of Energy, stating that energy cannot be created or destroyed, only transferred or transformed ($\Delta E = Q + W$); living cells must capture energy from external sources (such as food or light) rather than creating it.

Second Law of Thermodynamics

The principle stating that every energy transfer or transformation increases the entropy (disorder) of the universe, with a portion of usable energy inevitably dissipating as unusable heat.

Entropy ($S$)

A quantitative measure of disorder or randomness in a system representing unusable energy; natural processes lead to an increase in entropy unless work is actively invested.

Enthalpy ($H$)

The total energy content of a thermodynamic system, defined by the relationship $H = G + TS$, where $G$ is free energy, $T$ is absolute temperature in Kelvin ($\text{K}$), and $S$ is entropy.

Free Energy ($G$)

The portion of a system's total energy that is available to perform cellular work (such as building proteins or moving substances) at uniform temperature and pressure.

Exergonic Reaction

A spontaneous chemical reaction that releases usable free energy into its surroundings, characterized by a negative change in free energy ($\Delta G < 0$).

Endergonic Reaction

A non-spontaneous chemical reaction that requires an input of free energy, resulting in products that store more free energy than the reactants ($\Delta G > 0$).

Catabolism (Catabolic Pathways)

Metabolic pathways that break down large, energy-rich molecules into smaller molecules, releasing usable energy stored in temporary carriers such as $\text{ATP}$ and $\text{NADH}$.

Anabolism (Anabolic Pathways)

Biosynthetic metabolic pathways that assemble complex macromolecules from simpler precursors, requiring an input of energy typically supplied by $\text{ATP}$ or $\text{NADPH}$.

Energy Coupling

The cellular mechanism of linking an exergonic catabolic reaction to an endergonic anabolic reaction, using the energy released by breakdown to drive synthesis.

ATP Hydrolysis

The exergonic breakdown of adenosine triphosphate into adenosine diphosphate and inorganic phosphate ($\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i$), yielding $\Delta G = -7.3\,\text{kcal/mol}$ under standard conditions to power cellular work.

Activation Energy ($E_a$)

The initial investment of energy required to contort chemical bonds in reactant molecules to initiate a chemical reaction; biological catalysts (enzymes) speed up reactions by lowering this barrier.

Substrate

The specific reactant molecule upon which an enzyme acts and binds at its active site.

Competitive Inhibition

A mode of enzyme regulation where an inhibitor molecule directly mimics the substrate and binds to the active site, physically blocking the substrate from entering.

Noncompetitive Inhibition

Inhibition in which a molecule binds to an allosteric site away from the active site, inducing a conformational shape change in the enzyme that prevents it from functioning effectively.

Allosteric Site

A specific regulatory receptor site on an enzyme located separate from the active site, where the binding of effector molecules alters the enzyme's conformation and catalytic activity.

Feedback Inhibition

A negative feedback mechanism wherein the end product of a metabolic pathway allosterically inhibits an enzyme that catalyzes an earlier step in the pathway, preventing excess production.

Covalent Modification

The rapid regulation of enzyme activity through the addition or removal of chemical groups, such as phosphorylation via kinase enzymes or dephosphorylation via phosphatase enzymes.

Compartmentalization

The spatial segregation of enzymes and their specific substrates inside membrane-bound organelles to control reaction timing and prevent inappropriate interactions.

Cyanide

A potent noncompetitive metabolic poison that halts aerobic cellular respiration at the cellular level by blocking mitochondrial electron transport, causing asphyxiation despite abundant oxygen.

Substrate-Level Phosphorylation

The direct synthesis of $\text{ATP}$ by an enzyme transferring a phosphate group directly from a phosphorylated metabolic intermediate to $\text{ADP}$.

Chemiosmosis

The process of generating $\text{ATP}$ by establishing an electrochemical proton gradient across a membrane, which then powers $\text{ATP}$ synthase as protons flow back down the gradient by facilitated diffusion.

Aerobic Respiration

The oxygen-dependent catabolic breakdown of organic substrates (yielding $\text{CO}_2$ and $\text{H}_2\text{O}$) producing approximately $36\text{ to }38\,\text{ATP}$ per glucose molecule.

Lactic Acid Fermentation

An anaerobic pathway occurring in animal muscles and certain bacteria where pyruvate is reduced to lactic acid to reoxidize $\text{NADH}$ to $\text{NAD}^+$, generating a net yield of only $2\,\text{ATP}$ via glycolysis.

Alcohol Fermentation

An anaerobic pathway in yeast where pyruvate is converted to acetaldehyde with the release of $\text{CO}_2$, and acetaldehyde is reduced to ethanol to regenerate $\text{NAD}^+$ for glycolysis.

Photon

A discrete packet or quantum of electromagnetic energy with an energy content inversely proportional to its wavelength; capable of exciting orbital electrons in photosynthetic pigments.

Chlorophyll a

The primary photosynthetic pigment possessing a methyl ($-\text{CH}_3$) group that imparts a blue-green color; absorbs violet-blue and red light while reflecting green light.

Chlorophyll b

An accessory photosynthetic pigment possessing a carbonyl/formyl ($-\text{CHO}$) group that imparts a yellow-green or olive color, absorbing slightly shifted blue and red wavelengths.

Thylakoid Membrane

Interconnected flattened membranous sacs in the chloroplast, arranged in stacks called grana, where chlorophyll is embedded and the light-dependent reactions of photosynthesis take place.

Stroma

The dense fluid-filled space within the chloroplast surrounding the thylakoid membranes, serving as the site for the synthesis of carbohydrates during the light-independent reactions.

Stomata

Specialized microscopic pores on leaves flanked by guard cells that regulate transpirational water loss and gas exchange ($\text{CO}_2$ intake and $\text{O}_2$ release).