Week 5

Vocabulary practice flashcards covering membrane structure, phospholipid behavior, transport mechanisms, signal transduction, and cell scaling parameters.

Phospholipid

A lipid molecule composed of a polar, hydrophilic phosphate head and two non-polar, hydrophobic fatty acid tails.

Amphipathic

Describing a molecule that possesses both hydrophilic (water-attracted) and hydrophobic (water-repelled) regions, such as a phospholipid molecule.

Micelle

A spherical structure formed by phospholipids in water where hydrophilic heads face outward toward the aqueous solution and hydrophobic tails cluster inward, excluding water from the core.

Liposome

A spherical vesicle enclosed by a continuous phospholipid bilayer that encapsulates an aqueous central compartment.

Integral Protein

A permanently embedded membrane protein that penetrates the lipid bilayer, categorized as polytopic if spanning across the bilayer or monotopic if embedded in only one surface.

Peripheral Protein

A membrane protein temporarily associated with the inner or outer surface of the phospholipid bilayer or attached to integral proteins.

Glycoprotein

A protein attached to an oligosaccharide chain, involved in cell recognition by the immune system and serving as a hormone receptor.

Cholesterol

A steroid lipid in animal cell membranes containing a polar hydroxyl group, carbon rings, and a non-polar hydrocarbon tail; it regulates membrane fluidity and reduces permeability to hydrophilic solutes.

Davson-Danielli Model

A historical model of cell membrane structure proposing a central phospholipid bilayer sandwiched between two continuous outer layers of peripheral proteins.

Freeze-Fracture Technique

A cell preparation method involving rapid freezing and fracturing along lines of weakness in the membrane core, revealing globular structures inside the bilayer that falsified the Davson-Danielli model.

Singer-Nicholson Fluid Mosaic Model

The modern cell membrane model describing a fluid phospholipid bilayer wherein diverse proteins are embedded and capable of lateral movement.

Fluorescent Antibody Tagging

An experimental technique using red and green fluorescent antibody markers on membrane proteins to demonstrate lateral protein mobility after fusing human and mouse cells.

Passive Transport

The movement of molecules or ions across a biological membrane down a concentration gradient without requiring cellular energy.

Diffusion

The net passive movement of particles from an area of higher concentration to an area of lower concentration.

Facilitated Diffusion

The passive transport of polar, charged, or large molecules across a membrane down their concentration gradient via specific transmembrane channel or carrier proteins.

Aquaporin

A specialized integral transmembrane protein channel that speeds the movement of water molecules across the cell membrane.

Osmosis

The passive movement of water molecules across a selectively permeable membrane from an area of low solute concentration to high solute concentration.

Hypertonic Solution

A solution containing a higher concentration of solutes and lower concentration of water relative to the cell, causing net movement of water out of the cell.

Hypotonic Solution

A solution containing a lower concentration of solutes and higher concentration of water relative to the cell, causing net movement of water into the cell.

Isotonic Solution

A solution having an equal concentration of solutes and water relative to the cell, resulting in no net movement of water across the membrane.

Plasmolysis

The shrinking of a plant cell cytoplasm away from its cell wall when placed in a hypertonic solution due to osmotic water loss.

Turgid

The firm, swollen condition of a plant cell resulting from water entering the cell via osmosis when exposed to a hypotonic environment.

Active Transport

The movement of substances across a cell membrane against their concentration gradient (from low to high concentration), requiring cellular energy in the form of ATP.

ATP Hydrolysis

A chemical reaction using water to split ATP into ADP and an inorganic phosphate ion, releasing energy to drive cellular processes.

Primary Active Transport

Active transport that directly utilizes energy derived from the hydrolysis of ATP to pump molecules or ions against their concentration gradient.

Secondary Active Transport

Active transport where the required energy is derived from energy stored in the form of concentration differences of a second solute.

Proton Pump

An electrogenic transmembrane transport protein that uses ATP to pump hydrogen ions ($\text{H}^+$) out of the cell, generating voltage and a concentration gradient.

Cotransport Systems

Transmembrane transport mechanisms categorized as Uniport (moves one solute), Symport (moves two solutes in the same direction), or Antiport (moves two solutes in opposite directions).

Sodium-Potassium Pump

A primary active transport protein pump in animal cells that uses one ATP to pump three sodium ions ($3\,\text{Na}^+$) out of the axon and two potassium ions ($2\,\text{K}^+$) into the axon per cycle.

Endocytosis

An active cellular transport process where the plasma membrane invaginates to take substances into the cell within vesicles.

Exocytosis

An active transport process where intracellular vesicles fuse with the plasma membrane to export materials out of the cell.

Forms of Endocytosis

The three modes of endocytic uptake: Phagocytosis ('cell eating' of solid particles), Pinocytosis ('cell drinking' of fluid), and Receptor-Mediated Endocytosis (selective uptake via coated pits).

Regulated Secretion

Exocytosis that occurs in response to a specific stimulus or trigger, such as extracellular calcium ions ($\text{Ca}^{2+}$) triggering neurotransmitter release.

Constitutive Secretion

Exocytosis that occurs continuously in cells regardless of external signals, depending on the general function of the cell.

Membrane Potential

The electrical voltage measured across a cell membrane created by an unequal distribution of cations and anions.

Electrogenic Pump

A specialized transport protein that generates an electrical voltage across a membrane by transferring net charge across it.

G Protein-Coupled Receptor (GPCR)

A cell-surface transmembrane receptor that responds to signal molecules by activating a G protein bound by GTP.

Ligand-Gated Ion Channel

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

Phosphorylation Cascade

A signal transduction pathway in which a series of protein kinases sequentially phosphorylate and activate one another to produce a cellular response.

Cyclic AMP (cAMP)

A small intracellular second messenger molecule converted from ATP by adenylyl cyclase that activates protein kinase A during GPCR signaling.

Surface-Area-to-Volume Ratio (SA:Vol)

The proportion of a cell's outer boundary surface to its inner space; as cell volume increases, this ratio decreases, reducing transport and diffusion efficiency.

Paramecium

A single-celled organism that carries out all essential functions of life within one cell using organelles such as a contractile vacuole, oral groove, and cilia.