General Biology: Cell Structure, Membrane Transport, Metabolism, and Cellular Respiration

Comprehensive vocabulary flashcards covering eukaryotic and prokaryotic cell biology, organelles, membrane structure and transport mechanisms, thermodynamic principles, enzyme kinetics and regulation, and cellular respiration pathways.

Resolution

The ability of a microscope to distinguish two small objects that are close together as separate points.

Scanning Electron Microscope (SEM)

A microscope that focuses an electron beam onto the surface of a specimen to provide a 3-D image of the cell surface.

Transmission Electron Microscope (TEM)

A microscope that passes an electron beam through a thin section of a cell to visualize and highlight internal subcellular structures.

Cryo-Electron Microscopy

A microscopy technique that preserves cell samples at low temperatures to allow visualization of protein complexes and subcellular structures without fixatives or preservatives.

Cell Fractionation

A technique in which cells are broken apart and centrifuged at different speeds to separate major organelles and subcellular components based on size and density.

Nuclear Lamina

A net-like array of protein filaments lining the inner surface of the nuclear envelope that helps maintain the shape of the nucleus.

Endomembrane System

A collection of interrelated cellular membranes connected directly or via transport vesicles, including the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and plasma membrane.

Smooth Endoplasmic Reticulum

A region of the endoplasmic reticulum that lacks bound ribosomes; it functions in lipid synthesis, carbohydrate metabolism, chemical detoxification, and calcium ion storage.

Rough Endoplasmic Reticulum

A region of the endoplasmic reticulum studded with ribosomes on its outer surface; it produces transport vesicles and synthesizes secretory proteins such as glycoproteins.

Golgi Apparatus

An organelle consisting of stacks of flat membranous sacs (cisternae) that modifies, manufactures, sorts, and packages ER products into transport vesicles.

Autophagy

The recycling process in which lysosomes use their hydrolytic enzymes to break down and digest damaged organelles and cellular components.

Central Vacuole

A large membranous sac found in mature plant cells that holds sap, stores inorganic ions, and plays an essential role in plant growth and water regulation.

Endosymbiont Theory

The evolutionary theory proposing that mitochondria and plastids (including chloroplasts) originated as prokaryotic cells engulfed by an ancestral eukaryotic host cell.

Cristae

Infoldings of the inner mitochondrial membrane that provide a large surface area for enzymes synthesizing $\text{ATP}$.

Peroxisome

A specialized single-membrane metabolic organelle containing oxidative enzymes that transfer hydrogen to oxygen, producing hydrogen peroxide ($\text{H}_2\text{O}_2$).

Centrosome

A structure located near the nucleus in animal cells functioning as a microtubule-organizing center, containing a pair of centrioles composed of nine sets of triplet microtubules in a ring.

Microfilaments

Solid rods composed of two intertwined strands of actin monomers that bear tension, support cell shape in the cortex, drive muscle contraction with myosin, and enable amoeboid movement and cytoplasmic streaming.

Intermediate Filaments

Fibrous protein polymers coiled into thick cables (often made of keratins) that reinforce cell shape, anchor the nucleus and other organelles, and form the nuclear lamina.

Plant Cell Wall Layers

Extracellular structural layers of plant cells including the outermost thin primary cell wall, a pectin-rich middle lamella between adjacent walls, and a thick secondary cell wall between the plasma membrane and primary wall.

Extracellular Matrix (ECM)

A complex network of macromolecules secreted by animal cells, mainly composed of glycoproteins such as collagen, proteoglycans, and fibronectin, which bind to cell-surface integrins.

Plasmodesmata

Microscopic open channels traversing plant cell walls that connect the cytoplasm of adjacent cells, allowing the passage of water, solutes, proteins, and RNA.

Tight Junctions

Cell-to-cell junctions in animal epithelial tissues where neighbor cell membranes are pressed together tightly to establish a continuous barrier that prevents fluid leakage.

Desmosomes

Anchoring junctions that fasten animal cells together into strong, tear-resistant sheets, reinforced by intermediate filaments.

Gap Junctions

Communicating junctions between animal cells that provide cytoplasmic channels for the direct diffusion of ions, sugars, and small molecules.

Fluid Mosaic Model

The structural model of cell membranes describing them as a fluid phospholipid bilayer embedded with a mosaic of proteins, glycoproteins, glycolipids, and cholesterol.

Cholesterol (Membrane Buffer)

A steroid lipid found in animal cell membranes that modulates membrane fluidity by restraining phospholipid motion at warm temperatures and preventing tight tail packing at cool temperatures.

Aquaporin

A channel protein composed of four identical subunits that facilitates the rapid diffusion of water molecules across biological membranes at rates exceeding $3\times 10^9$ molecules per second.

Tonicity Effects on Animal Cells

The osmotic response of an animal cell causing it to swell and lyse in a hypotonic solution, remain stable in an isotonic solution, and lose water to become shriveled in a hypertonic solution.

Plasmolysis

The phenomenon in walled cells (plants and fungi) placed in a hypertonic medium, in which water is lost and the plasma membrane pulls away from the cell wall.

Facilitated Diffusion

The passive transport of polar molecules or ions across a biological membrane down their concentration gradient, assisted by channel or carrier transport proteins without energy expenditure.

Active Transport

The energy-requiring movement of a substance across a biological membrane against its concentration or electrochemical gradient, mediated by specific carrier proteins using $\text{ATP}$.

Membrane Potential

The voltage difference across a cell plasma membrane resulting from an unequal distribution of ions, usually making the intracellular face negatively charged relative to the outside.

Electrochemical Gradient

The combined gradient of concentration (chemical force) and electric charge (electrical force) that determines the passive diffusion direction of ions across a membrane.

Electrogenic Pump

An active transport protein that generates a net voltage across a membrane while translocating ions, such as the animal sodium-potassium pump ($\text{Na}^+/\text{K}^+$ ATPase) or the plant/fungal proton pump.

Cotransport

A mechanism in which the downhill diffusion of one substance drives the uphill active transport of another substance against its concentration gradient across a membrane.

Pinocytosis

A form of bulk endocytosis in which the cell non-specifically gulps droplets of extracellular fluid into tiny vesicles lined with coat proteins.

Receptor-Mediated Endocytosis

A selective bulk transport process in which extracellular ligands bind specific membrane receptors, causing clustering in coated pits that invaginate to form coated vesicles.

Catabolic Pathway

A metabolic pathway that releases free energy by breaking down complex molecules into simpler compounds, such as cellular respiration.

Anabolic Pathway

A biosynthetic metabolic pathway that consumes energy to build complicated molecules from simpler ones, such as protein synthesis.

First Law of Thermodynamics

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

Second Law of Thermodynamics

The thermodynamic principle stating that every energy transfer or transformation increases the entropy of the universe, with some energy inevitably converted to heat.

Free Energy ($\Delta G$)

The portion of a biological system's energy that can perform work under uniform temperature and pressure, defined by $\Delta G = \Delta H - T\Delta S$.

Exergonic Reaction

A spontaneous chemical reaction with a net release of free energy ($\Delta G < 0$) in which products have less free energy than reactants.

Endergonic Reaction

A non-spontaneous chemical reaction that absorbs free energy from its surroundings ($\Delta G > 0$), yielding products richer in free energy than reactants.

Energy Coupling

The use of an exergonic process to drive an endergonic process, primarily mediated through the hydrolysis of $\text{ATP}$.

Phosphorylated Intermediate

A molecule that has covalently received a phosphate group from $\text{ATP}$, rendering it less stable and more reactive than the unphosphorylated molecule.

Activation Energy ($E_A$)

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

Induced Fit

The slight conformational change of an enzyme's active site upon substrate binding that positions catalytic chemical groups into an optimal orientation to perform the reaction.

Coenzyme

An organic cofactor, such as vitamins or their derivatives, required by an enzyme to assist in catalysis.

Competitive Inhibitor

A substance that reduces enzyme activity by binding directly to the active site in competition with the substrate, mimicking its shape.

Noncompetitive Inhibitor

A substance that impedes enzyme activity by binding to a location away from the active site, inducing a conformational change that reduces catalytic efficiency.

Allosteric Regulation

The modulation of enzyme activity occurring when a regulatory molecule binds to a specific non-active site, stabilizing either an active or inactive conformation of the protein.

Feedback Inhibition

A regulatory mechanism in which the end-product of a metabolic pathway allosterically inhibits an enzyme acting early in that same pathway to avoid wasting chemical resources.

Oxidation

The complete or partial loss of electrons from a substance in a redox reaction, accompanied by an increase in oxidation state.

Reduction

The complete or partial addition of electrons to a substance in a redox reaction, accompanied by a decrease in oxidation state.

$$\text{NAD}^+$$

Nicotinamide adenine dinucleotide, an organic coenzyme and oxidizing agent that accepts two electrons and one proton ($\text{H}^+$) to become $\text{NADH}$ during respiration.

Glycolysis

The cytosolic ten-step anaerobic breakdown of one glucose molecule into two molecules of pyruvate, yielding a net of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Substrate-Level Phosphorylation

The enzyme-catalyzed direct transfer of a phosphate group from an organic substrate molecule to $\text{ADP}$, generating $\text{ATP}$.

Pyruvate Oxidation

The oxidative conversion of pyruvate into acetyl $\text{CoA}$ in the mitochondrial matrix (or prokaryotic cytosol), releasing $\text{CO}_2$ and producing $\text{NADH}$.

Citric Acid Cycle

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

Oxidative Phosphorylation

The production of $\text{ATP}$ using energy derived from the redox reactions of an electron transport chain and driven by chemiosmosis across the inner mitochondrial membrane.

Chemiosmosis

An energy-coupling mechanism that utilizes the proton-motive force generated by an electron transport chain to drive the synthesis of $\text{ATP}$ via $\text{ATP}$ synthase.

Alcohol Fermentation

An anaerobic catabolic pathway in which pyruvate from glycolysis is converted to acetaldehyde and then reduced by $\text{NADH}$ to ethanol, releasing $\text{CO}_2$ and regenerating $\text{NAD}^+$.

Lactic Acid Fermentation

An anaerobic catabolic pathway in which pyruvate is directly reduced by $\text{NADH}$ to form lactate without the release of $\text{CO}_2$, regenerating $\text{NAD}^+$ for continued glycolysis.