Cell Biology Lecture Notes Ch.5-8 Exam 2 Study Plasma Membranes, Bioenergetics, Cellular Respiration, and Photosynthesis

Comprehensive vocabulary flashcards covering membrane structure and transport, thermodynamics, metabolic pathways, enzyme mechanics, cellular respiration, and photosynthetic adaptations from biology lecture notes and review activities.

Fluid Mosaic Model

A structural model of the cell membrane describing it as a dynamic mosaic of components—including a phospholipid bilayer, transmembrane proteins, an interior protein network, and cell surface carbohydrate markers—that move fluidly within the plane of the membrane.

Phospholipid Bilayer

The structural foundation of plasma membranes, composed of two layers of amphipathic phospholipids arranged with their polar hydrophilic heads (glycerol and phosphate group) oriented outward toward aqueous environments and nonpolar hydrophobic fatty acid tails pointing inward.

Integral Membrane Proteins

Proteins integrated completely into the lipid bilayer that possess one or more hydrophobic membrane-spanning regions composed of nonpolar amino acids and hydrophilic regions exposed to aqueous solutions on either side.

Peripheral Membrane Proteins

Membrane proteins that do not span the lipid bilayer but are attached to the interior or exterior membrane surfaces, often anchoring cytoskeleton fibers or interacting with integral proteins.

Cholesterol

A lipid steroid found within the fatty acid core of animal cell plasma membranes that acts as a fluidity buffer, preventing membranes from becoming overly rigid at low temperatures or excessively fluid at high temperatures.

Selective Permeability

A property of cellular membranes that allows some substances to pass freely, requires specific transport mechanisms for others, and completely excludes certain substances, thereby maintaining internal cellular homeostasis.

Simple Diffusion

The passive movement of small, nonpolar molecules (such as $O_2$ and $CO_2$) directly through the phospholipid bilayer from an area of higher concentration to an area of lower concentration without energy expenditure.

Facilitated Diffusion

Passive transport of polar molecules and ions down their concentration gradient through the membrane mediated by transmembrane proteins (channel or carrier proteins) without consuming cellular energy.

Aquaporins

Channel proteins embedded within biological membranes that facilitate the rapid, selective passage of water ($H_2O$) molecules into and out of the cell.

Osmosis

The net passive movement or diffusion of water across a selectively permeable membrane from a region of lower solute concentration (higher free water) toward a region of higher solute concentration (lower free water).

Tonicity

The capacity of an extracellular solution to alter a cell's volume by promoting the osmotic influx or efflux of water, categorized into hypotonic, hypertonic, and isotonic conditions.

Electrochemical Gradient

A combined spatial gradient consisting of both a chemical concentration gradient and an electrical charge differential across a membrane, characterized by a negatively charged interior cytoplasm relative to the extracellular fluid.

Sodium-Potassium Pump ($Na^+/K^+$ Pump)

An electrogenic primary active transport antiporter that hydrolyzes one molecule of $ATP$ to pump $3\,Na^+$ ions out of the cell and $2\,K^+$ ions into the cell against their respective concentration gradients.

Secondary Active Transport

The active transport of a substance against its concentration gradient (such as glucose or amino acids) coupled to the passive movement of an ion down an electrochemical gradient previously established by primary active transport.

Phagocytosis

A type of endocytosis ('cellular eating') in which the plasma membrane wraps around and engulfs large particulate matter, whole cells, or macromolecules to enclose them in an internal vacuole or vesicle.

Pinocytosis

A form of endocytosis ('cellular drinking') where the cell membrane invaginates to take in small droplets of extracellular fluid and dissolved solutes within small vesicles.

Receptor-Mediated Endocytosis

A selective bulk import pathway where specific target substances bind to receptor proteins clustered in membrane-coated pits, triggering the inward budding and pinching off of specialized vesicles.

Exocytosis

The bulk transport process by which intracellular vesicles fuse with the plasma membrane to release their contents into the extracellular environment.

Anabolic Reactions

Metabolic chemical reactions (such as dehydration synthesis) that assemble complex polymers from simpler monomeric subunits, requiring an input of energy.

Catabolic Reactions

Metabolic pathways (such as hydrolysis) that break down large, complex molecules into simpler products, releasing usable chemical energy.

First Law of Thermodynamics

The principle of conservation of energy stating that energy cannot be created or destroyed; it can only change form from one state to another (e.g., potential to kinetic), keeping total energy in the universe constant.

Second Law of Thermodynamics

The physical law stating that energy transformations proceed spontaneously toward greater entropy (disorder) in the universe, with a portion of usable free energy inevitably dissipated as heat.

Gibbs Free Energy ($\Delta G$)

The portion of a thermodynamic system's energy capable of performing cellular work, governed by the equation $\Delta G = \Delta H - T\Delta S$, where $\Delta H$ represents enthalpy change, $T$ is temperature in Kelvins, and $\Delta S$ is entropy change.

Endergonic Reaction

A non-spontaneous chemical reaction that requires a net input of free energy ($\Delta G > 0$), yielding products that possess greater free energy than the initial reactants.

Exergonic Reaction

A spontaneous chemical reaction that releases energy ($\Delta G < 0$), producing products that have lower free energy than the starting reactants.

Activation Energy ($E_a$)

The minimum amount of energy required to destabilize chemical bonds in reactants and force them into a high-energy, unstable transition state to initiate a reaction.

ATP Cycle

The continual cellular cycle wherein $ATP$ is hydrolyzed into $ADP$ and inorganic phosphate ($P_i$) by $ATP$ hydrolase to release energy for cellular work, and resynthesized from $ADP$ and $P_i$ by $ATP$ synthase using catabolic energy.

Induced Fit

A model of enzyme-substrate interaction wherein the binding of a substrate induces a dynamic conformational shift in the enzyme's active site, aligning catalytic residues to lower activation energy.

Competitive Inhibition

A mechanism of enzyme inhibition where an inhibitor molecule structurally mimics the substrate and competes directly for occupancy of the active site, reducing reaction rates without altering the maximum velocity ($V_{\max}$).

Noncompetitive Inhibition

A form of enzyme regulation where an inhibitor binds to an allosteric site away from the active site, inducing a conformational change that lowers catalytic efficiency and decreases the maximal rate ($V_{\max}$).

Feedback Inhibition

A biochemical regulation mechanism in which the final end product of a multi-step metabolic pathway allosterically inhibits an enzyme that catalyzes an earlier, upstream step in the pathway.

Redox Reaction

A coupled chemical reaction involving the transfer of electrons from one species to another, consisting of oxidation (loss of electrons) and reduction (gain of electrons).

Substrate-Level Phosphorylation

The direct synthesis of $ATP$ by transferring a high-energy phosphate group from a phosphorylated metabolic intermediate substrate directly to $ADP$, occurring in glycolysis and the citric acid cycle.

Oxidative Phosphorylation

The production of $ATP$ powered by chemiosmosis, in which an electrochemical proton gradient generated across the inner mitochondrial membrane by the electron transport chain drives $ATP$ synthesis via $ATP$ synthase.

Glycolysis

A ten-step anaerobic metabolic pathway occurring in the cytosol that cleaves one $6$-carbon glucose molecule into two $3$-carbon pyruvate molecules, with a net yield of $2\,ATP$ and $2\,NADH$.

Pyruvate Oxidation

The aerobic transition stage occurring in the mitochondrial matrix where each $3$-carbon pyruvate is decarboxylated and oxidized to a $2$-carbon acetyl group attached to coenzyme A, yielding $1\,CO_2$ and $1\,NADH$ per pyruvate.

Citric Acid Cycle

An eight-step cyclic pathway in the mitochondrial matrix that oxidizes acetyl-CoA into $CO_2$, producing $1\,ATP$, $3\,NADH$, and $1\,FADH_2$ per turn ($2\,ATP$, $6\,NADH$, and $2\,FADH_2$ per glucose molecule).

Electron Transport Chain (Cellular Respiration)

A sequence of multiprotein electron carriers (Complexes I–IV) and shuttles (ubiquinone, cytochrome c) embedded in the inner mitochondrial membrane that pump protons into the intermembrane space as electrons travel to terminal oxygen ($O_2$).

Fermentation

An anaerobic pathway that allows glycolysis to proceed in the absence of oxygen by using an organic molecule as a terminal electron acceptor to re-oxidize $NADH$ back to $NAD^+$.

Phosphofructokinase (PFK)

The primary regulatory allosteric enzyme of glycolysis that catalyzes the conversion of fructose-$6$-phosphate to fructose-$1,6$-bisphosphate, stimulated by high $ADP$/$AMP$ and inhibited by high $ATP$, citrate, or low pH.

Light-Dependent Reactions

Photosynthetic reactions occurring within the thylakoid membranes of chloroplasts that capture solar photon energy to split water ($H_2O$), release oxygen ($O_2$), and synthesize $ATP$ and $NADPH$.

Photosystem II (PSII)

A multiprotein light-harvesting complex in thylakoid membranes that absorbs photon energy to excite electrons into an electron transport chain and carries out the photolysis of water ($H_2O \rightarrow 2\,H^+ + 2\,e^- + \frac{1}{2}O_2$) to replace lost electrons.

Calvin Cycle

The stroma-localized, light-independent pathway of photosynthesis comprising carbon fixation, reduction, and $RuBP$ regeneration, utilizing $ATP$ and $NADPH$ to synthesize glyceraldehyde-$3$-phosphate ($G3P$) from $CO_2$.

RuBisCO

Ribulose-$1,5$-bisphosphate carboxylase/oxygenase; the stroma enzyme that catalyzes the primary carbon-fixation reaction by attaching $CO_2$ to ribulose-$1,5$-bisphosphate ($RuBP$), but can also fix $O_2$ during photorespiration.

Photorespiration

An energetically wasteful pathway in plants occurring when RuBisCO binds oxygen ($O_2$) rather than carbon dioxide ($CO_2$), yielding $2$-phosphoglycolate and consuming $ATP$ and $NADPH$ without producing sugars.

$C_4$ Pathway

A photosynthetic adaptation providing spatial separation of carbon fixation between mesophyll cells (using PEP carboxylase to form a $4$-carbon acid) and bundle-sheath cells (where $CO_2$ is released around RuBisCO) to minimize photorespiration.

CAM Photosynthesis

Crassulacean Acid Metabolism; a photosynthetic adaptation that temporally separates gas exchange and carbon usage by opening stomata at night to fix $CO_2$ into malic acid stored in vacuoles, and closing stomata by day to decarboxylate acids for the Calvin cycle.

Comparative Photosynthetic Adaptations

Distinct evolutionary strategies for carbon fixation: $C_3$ plants fix $CO_2$ directly via RuBisCO in mesophyll cells, $C_4$ plants utilize spatial separation between mesophyll and bundle-sheath cells, and CAM plants rely on temporal night-versus-day separation.