Structure and Function of Plasma Membranes - Vocabulary Flashcards

Vocabulary-style flashcards covering key terms related to plasma membranes, transport mechanisms, and osmoregulation from the lecture notes.

Phospholipid

Amphiphilic lipid with two fatty acid (nonpolar) tails, a glycerol backbone, and a phosphate-containing polar head; forms the phospholipid bilayer.

Phospholipid Bilayer

Two layers of phospholipids with polar heads facing outward and hydrophobic tails facing inward.

Fluid Mosaic Model

Membrane structure modeled as a mosaic of lipids, proteins, cholesterol, and carbohydrates that gives the membrane a fluid character; proposed by Singer and Nicolson (1972).

Integral Membrane Protein

Proteins embedded throughout the bilayer; often hydrophobic in regions and contribute to transport, receptors, enzymes, etc.

Peripheral Membrane Protein

Proteins attached to the membrane surface, not embedded in the bilayer.

Amphipathic/Amphipathic Molecule

Molecule that has both hydrophilic (water-loving) and hydrophobic (water-fearing) regions, like phospholipids.

Channel Protein

Transmembrane protein that forms a pore for specific ions or polar molecules to diffuse down their gradient; can be always open or gated.

Aquaporin

A channel protein specialized for rapid water diffusion across the membrane.

Carrier Protein

Transmembrane protein that binds a specific substance and changes shape to shuttle it across the membrane; can be bidirectional.

GLUTs (Glucose Transport Proteins)

Carrier proteins that specifically transport glucose across the membrane.

Glycoprotein

Protein with carbohydrate chains attached; located on the exterior surface of the membrane and involved in cell recognition.

Glycolipid

Lipid with carbohydrate chains attached; located on the exterior membrane surface and contributes to the glycocalyx.

Cholesterol (membrane)

Sterol in the fatty acid layer that buffers membrane fluidity, keeping membranes fluid at low temps and more rigid at high temps.

Membrane Asymmetry

The inner and outer surfaces of the plasma membrane differ in composition and protein orientation.

Osmosis

Diffusion of water across a membrane from higher water concentration to lower water concentration, driven by solute differences.

Diffusion

Movement of molecules from high to low concentration; in membranes, small nonpolar molecules can diffuse through the lipid bilayer.

Facilitated Diffusion

Passive transport of substances down their concentration gradient via channel or carrier proteins.

Passive Transport

Movement of substances down their gradient that requires no energy input.

Active Transport

Movement of substances against their concentration or electrochemical gradient, requiring energy (ATP or ions/electrochemical gradients).

Primary Active Transport

Direct use of energy (usually ATP hydrolysis) to move substances against their gradient.

Na+/K+ Pump

Primary active transport pump that moves 3 Na+ out and 2 K+ in; electrogenic and helps maintain membrane potential.

Electrochemical Gradient

Combined effect of concentration gradient and electrical gradient across the membrane; drives transport processes.

Proton Gradient

Gradient of H+ ions across a membrane generated by proton pumps; can drive ATP synthesis or transport.

Symporter

Carrier that moves two different substances in the same direction across the membrane.

Antiporter

Carrier that moves two different substances in opposite directions across the membrane.

Uniporter

Carrier that transports a single type of molecule or ion across the membrane.

Endocytosis

Bulk transport into the cell via vesicle formation; includes phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Phagocytosis

Cellular eating; membrane engulfs large particles into a vacuole.

Pinocytosis

Cellular drinking; membrane invaginates to form vesicles that internalize extracellular fluid.

Receptor-Mediated Endocytosis

Selective uptake of specific molecules via receptors on the membrane that trigger vesicle formation.

Exocytosis

Process by which vesicles fuse with the plasma membrane to release contents outside the cell.

Turgor Pressure

Pressure exerted by the plasma membrane against the cell wall in plants; essential for growth.

Plasmolysis

Detachment of the plasma membrane from the cell wall due to hypertonic extracellular solutions.

Osmoregulation

Regulation of solute concentrations and water balance; occurs in plants, protists, marine animals, and vertebrates.

Isotonic

Extracellular solution with the same osmolarity as the cytosol; no net water movement.

Hypertonic

Extracellular solution with higher osmolarity than cytosol; water moves out of the cell.

Hypotonic

Extracellular solution with lower osmolarity than cytosol; water moves into the cell.

Osmolarity

Total solute concentration of a solution (permeable and nonpermeable solutes).

Contractile Vacuole

Organelle in freshwater protists that pumps water out to prevent bursting.

Electrogenic Pump

Pump that contributes to the charge difference across the membrane (e.g., Na+/K+ pump).

ATP Hydrolysis

Catabolic reaction that releases energy used by primary active transport and other cellular processes.

CD4 Receptor Glycoprotein

T-cell receptor glycoprotein that can recognize HIV as self, illustrating membrane protein roles in immune recognition.