Bio 1020 Exam 2 Lazenby - Cell Membranes

Self-sealing property

Membranes automatically reseal when broken or pinched.

Vesicle formation

Created when regions of membrane are pinched off by protein contractile rings.

Fusion

Occurs when two membrane surfaces come into close contact, mixing contents of two separate lumens.

Vesicle-plasma membrane fusion

Releases materials to outside the cell (exocytosis).

Integral proteins

Amphipathic (hydrophobic + hydrophilic regions), firmly bound; removable only by detergents.

Transmembrane proteins

Span entire bilayer and often have hydrophobic α-helices in spanning regions.

Peripheral proteins

Not embedded in membrane; attached ionically or by H-bonds to hydrophilic parts of integral proteins or lipid heads.

Asymmetry of Membranes

Protein composition differs on each side; cytoplasmic side usually has more proteins.

Functions of Membrane Proteins

Includes enzymatic activity, transport regulation, and cell signaling.

Selective Permeability

Membranes allow some molecules to pass while blocking others.

Diffusion

Movement of molecules from high → low concentration (down gradient) driven by random motion.

Osmosis

Movement of water across a selectively permeable membrane affected by solutes.

Osmotic pressure

Tendency of water to move into a solution.

Isotonic

Equal solute concentrations with no net water movement.

Hypertonic

Higher solute concentration causing water to move out → cell shrinks.

Hypotonic

Lower solute concentration causing water to move in → cell swells/bursts (animal).

Turgor Pressure

Pressure of the cell membrane against the cell wall due to water uptake, preventing bursting and maintaining rigidity.

Facilitated Diffusion

Movement down concentration gradient with help of transport proteins, requiring no energy.

Active Transport

Moves substances against concentration gradient (low → high) and requires energy (ATP).

Cotransport

One ion moves down its gradient, releasing energy that drives another molecule up its gradient.

Exocytosis

Vesicles fuse with plasma membrane → release material outside cell.

Endocytosis

Vesicle forms from plasma membrane → brings material into cell.

Phagocytosis

Cell 'eating' of large particles (e.g., bacteria).

Pinocytosis

'Cell drinking' of dissolved materials.

Receptor-mediated endocytosis

Specific molecules bind to receptors → trigger coated vesicle formation.

Signal Transduction

Receptor proteins bind signaling molecules outside the cell, triggering an internal cascade.

Anchoring Junctions (Desmosomes)

Hold cells tightly together, merging cytoskeletons, strong but allow material passage between cells.

Tight Junctions

Seal off spaces between cells, preventing passage between cells.

Gap Junctions

Allow direct communication between cells through cylindrical protein channels.

Plasmodesmata

Allow communication & transport between plant cells through channels in cell walls.