Phospholipids:
Key components of the membrane.
Arranged in a bilayer, forming the fundamental structure.
Fluid Mosaic Model: Proteins float in or on the fluid lipid bilayer.
Components of Membrane:
Phospholipid Bilayer: Flexible matrix, acts as a permeability barrier.
Transmembrane Proteins: Integral membrane proteins extending across the lipid bilayer.
Interior Protein Network: Peripheral membrane proteins supporting the structure.
Cell Surface Markers: Glycoproteins and glycolipids that identify cells.
Components:
Glycerol: A three-carbon molecule.
Fatty Acids: Two nonpolar, hydrophobic fatty acids.
Phosphate Group: Polar and hydrophilic, forming the head.
Bilayer Formation:
Spontaneously forms with fatty acids facing inward and phosphate heads facing outward.
Fluidity Characteristics:
Lateral Movement: Phospholipids move laterally ~107 times per second.
Flip-Flop Movement: ~Once per month, where phospholipids switch layers.
Factors Influencing Fluidity:
Saturated vs Unsaturated Fatty Acids:
Unsaturated fatty acids introduce kinks, preventing tight packing, leading to increased fluidity.
Cholesterol: Acts as a buffer for fluidity depending on temperature.
Functions:
Transporters: Move substances across the membrane.
Enzymes: Catalysts for reactions.
Cell-Surface Receptors: Communicate signals.
Identity Markers: Help cells recognize each other.
Adhesion Proteins: Attach cells to each other or extracellular matrix.
Cytoskeleton Attachment: Contributes to the shape and structure of the cell.
Integral Membrane Proteins:
Span the lipid bilayer with nonpolar regions inside and polar regions protruding outward.
Transmembrane Domain: Contains hydrophobic amino acids typically arranged in alpha helices.
Passive Transport:
No Energy Required: Movement down a concentration gradient.
Diffusion: Molecules move from high to low concentrations until equilibrium is reached.
Facilitated Diffusion:
Molecules that cannot easily cross membranes move through protein channels or carriers.
Channel Proteins: Form hydrophilic channels for ions.
Carrier Proteins: Specific to the solute, change shape to transport it.
Active Transport:
Energy Required: Moves substances against their concentration gradients using ATP.
Example: Sodium-Potassium Pump: Moves Na+ out of the cell and K+ into the cell.
Definition: Net diffusion of water across a selectively permeable membrane towards higher solute concentration.
Types of Solutions:
Hypertonic: Higher solute concentration leading to water loss in cells.
Hypotonic: Lower solute concentration leading to water intake and possible cell lysis.
Isotonic: Equal solute concentrations; no net movement.
Mechanism: Large quantities or molecules use vesicles to cross membranes.
Exocytosis: Expulsion of materials from the cell.
Endocytosis: Intake of materials into the cell through invagination of the plasma membrane.
Types of endocytosis:
Phagocytosis: Engulfing of particles.
Pinocytosis: Intake of fluids.
Receptor-Mediated Endocytosis: Specific molecules bind to receptors to trigger a vesicle formation.