Cell Biology, Transport, Metabolism, and Communication

A comprehensive vocabulary review deck covering large biological molecules, membrane transport mechanisms, energy and cellular metabolism, and cell communication pathways based on introductory biology lectures.

Information Flow

The transmission and reception of information occurring when a cell receives a signal from its external environment and responds with biochemical changes that affect its functions.

Ligand

A signalling molecule that binds specifically to a receptor protein to initiate cell communication.

Cell Signalling Stages

The three sequential steps of cell communication consisting of reception (ligand binding to receptor), transduction (converting the signal into a relayable form), and cellular response (activation of cellular activity).

Signal Transduction

The multi-step process that converts a received extracellular signal into a specific form that can trigger a cellular response.

Second Messengers

Small, non-protein, water-soluble molecules or ions—such as $\text{cAMP}$, $\text{IP}_3$, and $\text{Ca}^{2+}$—that relay signals inside the cell during transduction.

G-Protein Coupled Receptor (GPCR)

A cell-surface transmembrane receptor that works with the assistance of a G protein to activate intracellular enzymes or pathways upon ligand binding.

Ligand-Gated Ion Channel Receptor

A membrane receptor containing a region that acts as a gate, opening or closing in response to the binding of a specific signalling molecule to allow or block the passage of ions.

Endocrine Signalling

Long-distance cell communication where hormones are secreted into body fluids to reach distant target cells.

Paracrine Signalling

A form of local cell signalling where molecules released by a cell diffuse through extracellular fluid to affect nearby target cells.

Autocrine Signalling

A form of cell signalling in which a cell secretes a chemical messenger that binds to receptors on its own surface, affecting itself.

Phospholipase C

An intracellular enzyme activated by a G protein that cleaves the membrane lipid $\text{PIP}_2$ into the second messengers $\text{IP}_3$ and $\text{DAG}$.

TrpM5

A cation channel in taste cells opened by cytosolic $\text{Ca}^{2+}$ influx, resulting in membrane depolarization.

Panx1 Hemichannel

A membrane channel in taste cells opened by depolarization and $\text{Ca}^{2+}$ action, allowing $\text{ATP}$ to flow out of the cell to stimulate nearby neurons.

Sweet Taste Transduction Pathway

A complex signalling cascade where sweet tastants bind to GPCR heterodimers ($\text{T1R2}$ + $\text{T1R3}$), activating phospholipase C, releasing cytosolic $\text{Ca}^{2+}$, opening $\text{TrpM5}$ and $\text{Panx1}$ channels, and releasing $\text{ATP}$.

Metabolism

The totality of an organism's chemical reactions, consisting of catabolic and anabolic pathways that manage the material and energy resources of the cell.

Anabolic Pathways

Non-spontaneous, endergonic metabolic pathways that consume energy to build complex molecules from simpler ones.

Catabolic Pathways

Spontaneous, exergonic metabolic pathways that release energy by breaking down complex molecules into simpler compounds.

Endergonic Reaction

A non-spontaneous chemical reaction that absorbs energy from its surroundings, characterized by a positive change in free energy ($\Delta G > 0$).

Exergonic Reaction

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

Potential and Kinetic Energy Transformation

The conversion between energy stored in matter due to its position or structure (potential energy) and energy associated with the relative motion of objects (kinetic energy).

Cellular Respiration

The catabolic pathway of ATP production in which organic fuel molecules like glucose are broken down in a series of exergonic redox reactions.

Substrate-Level Phosphorylation

The direct transfer of a phosphate group from an organic substrate molecule to ADP to form ATP by an enzyme, as occurs in glycolysis and the citric acid cycle.

Oxidative Phosphorylation

The production of ATP using energy derived from the redox reactions of an electron transport chain and chemiosmosis across a membrane.

Chemiosmosis

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

Passive Transport

The movement of substances across a biological membrane down their concentration gradient without requiring an input of cellular energy.

Facilitated Diffusion

The passive transport of polar molecules or ions across a membrane down their concentration gradient mediated by channel or carrier proteins.

Active Transport

The movement of a substance across a cell membrane against its concentration gradient, requiring energy input (usually ATP hydrolysis) and carrier proteins.

Sodium-Potassium Pump (\text{Na}^+/\text{K}^+ Pump)

An electrogenic transport protein that uses ATP hydrolysis to actively pump three $\text{Na}^+$ ions out of the cell for every two $\text{K}^+$ ions pumped into the cell.

Cotransport

A process in which the active transport of one solute is coupled to and indirectly driven by the downhill diffusion of another solute whose concentration gradient is maintained by a primary pump.

Tight Junctions

Intercellular junctions between adjacent epithelial cells that seal the extracellular space, preventing solute leakage and maintaining distinct apical and basal membrane domains.

Apical Membrane

The surface domain of an epithelial cell that faces an open space or lumen, often specialized with microvilli to increase membrane surface area for absorption or detection.

Basal Membrane

The surface domain of an epithelial cell oriented away from the lumen toward underlying tissues and blood capillaries.

Functional Groups

Specific reactive configurations of atoms attached to carbon skeletons that confer unique chemical properties, shape, and reactivity to organic molecules.

Glycosidic Linkage

A covalent bond formed between two monosaccharide units by a dehydration reaction.

Phospholipids

Amphipathic lipid molecules composed of a hydrophilic head (glycerol and phosphate) and two hydrophobic fatty acid tails, serving as the essential building blocks of cell membranes.

Phospholipid Bilayer

A two-layered arrangement of phospholipids that self-assembles in aqueous environments, positioning hydrophilic heads outward toward water and hydrophobic tails inward.

Saturated Fatty Acid

A fatty acid having no double bonds between carbon atoms in its hydrocarbon chain, allowing molecules to pack tightly into a solid at room temperature.

Unsaturated Fatty Acid

A fatty acid containing one or more double bonds in its hydrocarbon chain, creating kinks that prevent tight packing and keep it liquid at room temperature.

Primary Structure

The specific, linear sequence of amino acids linked by peptide bonds in a polypeptide chain, encoded by genetic information.

Secondary Structure

Localized, repetitive coiling or folding patterns within a polypeptide backbone (such as $\alpha$-helices and $\beta$-pleated sheets) stabilized by hydrogen bonds.

Tertiary Structure

The overall three-dimensional shape of a polypeptide chain resulting from interactions among various amino acid side chains (R groups).

Quaternary Structure

The overall protein structure formed by the association of two or more individual polypeptide subunits into a functional complex.

Transthyretin

A transport protein with a quaternary structure composed of four identical polypeptide subunits that functions in transporting thyroxine and retinol in the bloodstream.