Campbell Biology: Chapters 7-10 (Membrane Function, Metabolism, Cellular Respiration, and Photosynthesis)

Vocabulary practice flashcards covering cell membrane structure and selective permeability, bioenergetics and enzyme kinetics, cellular respiration stages and fermentation, and the light reactions and Calvin cycle of photosynthesis.

Fluid Mosaic Model

A model of cell membrane structure depicting the membrane as a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids.

Amphipathic Molecule

A molecule that possesses both a hydrophilic ('water-loving') region and a hydrophobic ('water-fearing') region, such as a phospholipid.

Membrane Fluidity Regulation by Hydrocarbon Tails

Membranes rich in unsaturated fatty acids remain fluid at lower temperatures because kinks in the tails prevent tight packing, whereas saturated fatty acid tails pack closely together, making membranes more viscous.

Cholesterol (in Animal Membranes)

A steroid membrane component in animal cells that acts as a fluidity buffer: it restrains phospholipid movement at warm temperatures (such as $37^\circ\text{C}$) and hinders tight packing at cool temperatures.

Integral Proteins

Membrane proteins that penetrate the hydrophobic interior of the lipid bilayer; those that span the entire membrane are termed transmembrane proteins.

Peripheral Proteins

Membrane proteins that are not embedded in the lipid bilayer, but are loosely bound to the surface of the membrane.

Glycolipids and Glycoproteins

Carbohydrates covalently bonded to lipids or proteins, respectively, on the extracellular surface of the plasma membrane that function as identification markers in cell-cell recognition.

Selective Permeability

A property of cellular membranes that allows some substances to cross more easily than others, permitting nonpolar molecules ($\text{O}_2$, $\text{CO}_2$, hydrocarbons) to cross rapidly while impeding ions and polar molecules.

Aquaporins

Channel proteins in the plasma membrane that specifically facilitate the rapid diffusion and passage of water ($\text{H}_2\text{O}$) molecules.

Diffusion

The spontaneous movement of particles of any substance down their concentration gradient so that they spread out evenly into available space without energy investment.

Osmosis

The diffusion of free water across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water, determined by solute concentrations that cannot cross the membrane relative to the intracellular fluid.

Active Transport

The movement of a substance across a cell membrane against its concentration gradient, mediated by specific carrier proteins and requiring energy expenditure, usually via ATP hydrolysis.

Sodium-Potassium Pump

A transport protein that hydrolyzes ATP to actively pump three $\text{Na}^+$ ions out of animal cells and two $\text{K}^+$ ions into the cell against their respective concentration gradients.

Electrogenic Pump

An active transport protein that generates voltage across a membrane by creating a net transfer of charge, such as the sodium-potassium pump in animals or the proton pump ($\text{H}^+$) in plants, fungi, and bacteria.

Cotransport

A mechanism in which the downhill diffusion of an energetically favored solute is coupled to the uphill transport of a second substance against its own concentration gradient.

Phagocytosis

A form of endocytosis ('cellular eating') where a cell engulfs large particles or whole cells by extending pseudopodia around them and packaging them within a food vacuole.

Pinocytosis

A form of endocytosis ('cellular drinking') where extracellular droplets are nonspecifically taken up into tiny coated vesicles formed from plasma membrane invaginations.

Receptor-Mediated Endocytosis

Targeted bulk uptake of specific solutes triggered when extracellular ligands bind to cell-surface receptors clustered in coated pits, pinching off to form coated vesicles.

Catabolic Pathways

Metabolic pathways that release energy by breaking down complex molecules into simpler compounds, such as cellular respiration breaking down glucose.

Anabolic Pathways

Metabolic pathways that consume energy to synthesize complex molecules from simpler precursors, such as assembling proteins from amino acids.

First Law of Thermodynamics

The principle of conservation of energy stating that energy can be transferred and transformed, but it cannot be created or destroyed.

Second Law of Thermodynamics

The physical law stating that every energy transfer or transformation increases the entropy (molecular disorder or randomness) of the universe.

Gibbs Free Energy ($G$)

The portion of a biological system's energy that can perform work when temperature and pressure are uniform throughout the system.

Exergonic vs. Endergonic Reactions

An exergonic reaction proceeds with a net release of free energy ($\Delta G < 0$) and is spontaneous, whereas an endergonic reaction absorbs free energy ($\Delta G > 0$) from its surroundings and is nonspontaneous.

Energy Coupling

The cellular strategy of using an exergonic process to drive an endergonic one, most commonly mediated by the hydrolysis of ATP.

Phosphorylated Intermediate

A molecule that has covalently received a phosphate group transferred from ATP, making it less stable, richer in free energy, and more reactive.

Activation Energy ($E_A$)

The initial investment of energy required to contort reactant molecules into an unstable transition state so chemical bonds can break and start a reaction.

Induced Fit

The slight change in shape of an enzyme's active site upon substrate binding that positions catalytic chemical groups to enhance reaction catalysis.

Competitive Inhibitors

Enzyme inhibitors that closely mimic the substrate's structure and reversibly bind to the active site, directly competing with the substrate for access.

Noncompetitive Inhibitors

Inhibitors that bind to an alternative site on an enzyme away from the active site, inducing a shape change that reduces catalytic efficiency.

Allosteric Regulation

The regulation of an enzyme's activity resulting from a regulatory molecule binding to a specific site outside the active site, stabilizing either its active or inactive conformation.

Feedback Inhibition

A regulatory mechanism in which the terminal product of a metabolic pathway allosterically inhibits an enzyme catalyzing an early step in that same pathway.

Redox Reactions

Chemical oxidation-reduction reactions involving the transfer of one or more electrons, where oxidation denotes electron loss and reduction denotes electron gain.

$\text{NAD}^+$ / $\text{NADH}$

A coenzyme functioning as an electron carrier in cellular respiration; nicotinamide adenine dinucleotide accepts two electrons and one proton ($\text{H}^+$) to cycle between oxidized ($\text{NAD}^+$) and reduced ($\text{NADH}$) states.

Substrate-Level Phosphorylation

The direct enzymatic transfer of a phosphate group from an organic substrate intermediate to ADP, occurring during glycolysis and the citric acid cycle.

Glycolysis

A ten-step cytoplasmic pathway that splits one glucose molecule into two molecules of pyruvate, generating a net output of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Pyruvate Oxidation

The enzymatic conversion of pyruvate into acetyl CoA within the mitochondrion by pyruvate dehydrogenase, releasing $\text{CO}_2$ and producing $\text{NADH}$.

Citric Acid Cycle

An eight-step metabolic cycle in the mitochondrial matrix that oxidizes acetyl CoA derived from pyruvate, producing $1\,\text{ATP}$, $3\,\text{NADH}$, $1\,\text{FADH}_2$, and $2\,\text{CO}_2$ per turn.

ATP Synthase

A multi-subunit membrane enzyme complex consisting of a rotor, stator, internal rod, and catalytic knob that utilizes proton gradient energy to drive the phosphorylation of ADP to ATP.

Chemiosmosis

An energy-coupling mechanism that uses energy stored in the form of a hydrogen ion ($\text{H}^+$) gradient across a membrane to drive cellular work, such as ATP synthesis.

Alcohol Fermentation

An anaerobic catabolic pathway in which pyruvate is converted to ethanol in two steps, releasing $\text{CO}_2$ and oxidizing $\text{NADH}$ back to $\text{NAD}^+$.

Lactic Acid Fermentation

An anaerobic pathway in which pyruvate is directly reduced by $\text{NADH}$ to form lactate and regenerate $\text{NAD}^+$ without producing $\text{CO}_2$.

Phosphofructokinase

An allosteric pacemaker enzyme of glycolysis inhibited by ATP and citrate, and stimulated by AMP, coordinating the pace of cellular respiration.

Photoautotrophs

Organisms that use light energy to drive the synthesis of organic molecules from carbon dioxide and water, serving as the primary producers of the biosphere.

Chloroplast

A photosynthetic organelle bounded by a double membrane containing dense fluid (stroma) and interconnected membranous sacs (thylakoids) arranged in grana.

Photosystem

A light-capturing unit located in the thylakoid membrane consisting of a reaction-center complex surrounded by several light-harvesting complexes containing pigment molecules.

Linear Electron Flow

The primary light-reaction pathway in thylakoid membranes involving both PS II and PS I, which splits $\text{H}_2\text{O}$ to produce ATP, NADPH, and release $\text{O}_2$.

Cyclic Electron Flow

An alternative light-driven electron pathway using only Photosystem I and the cytochrome complex to synthesize ATP without generating NADPH or releasing oxygen.

Rubisco

Ribulose bisphosphate carboxylase-oxygenase, the enzyme that catalyzes the first phase of the Calvin cycle by attaching $\text{CO}_2$ to ribulose bisphosphate (RuBP).

Calvin Cycle

An anabolic photosynthetic pathway occurring in the stroma that utilizes ATP and NADPH from the light reactions to reduce $\text{CO}_2$ into glyceraldehyde 3-phosphate (G3P).