Chapter 7-Life on the edgePlasma membrane is the boundary that separates the living cell from its surround.Cellular Permeability: Certain things cross easily other can’t.-Membrane Proteins6-FunctionsTransportEnzymatic ActivitySignal transductionCell-Cell RecognitionIntercellular Joining.Attachment to the cytoskeleton and extracellular matrix.-Concept 7.2 Cell must exchange with its surrounding.Plasmas membrane regulates molecular traffic.Control input (glucose) needed.Control output (urea, waste) not needed.-Permeability of the lipid bilayerHydrophobic molecule can move through membrane easily.Gases such as O2 and CO2 can cross, as well as lipids.Polar molecules, sugars, can’t cross easily cross, because of hydrophobic layer of membrane.-Transport proteinsAllow passage of hydrophilic substances across membrane.Channel proteins: Hydrophilic channel that certain molecules or ions can use as a tunnel.Bypasses the hydrophobic region.Aquaporin’s: Facilitate the passage of water.Carrier Proteins: bind to molecules change shape to shuttle them across the membrane.Transport protein is specific to one substance.Glucose only not fructose.-Concept 7.3: Passive transport is diffusion with no energy investment.Diffusion: Molecules spreading evenly into the available space.Although each molecule is random, diffusion can move in one direction.At dynamic equilibrium, rate of ions entering = rate of ions leaving cell.Substances diffuse down the concentration gradient.Movement is unaffected by the concentration of other substances.No work must be done to move substances down the concentration gradient.Diffusion is passive transport.- Delta G, Spontaneous, and exergonic.Simple diffusion is the movement of gases, and lipids through the phospholipid layer.Facilitated diffusion: For larger molecules helps from proteins to pass membrane.No energy.-Facilitated Diffusion: Passive TransportSpeed the passive movement of molecules across the plasma membrane.Transport proteinsChannel Proteins.AquaporinIon ChannelCarrier ProteinsSome diseases are caused by the malfunctions of specific transport systems, for example the kidney disease Cystinuria.Cysteine not transported back into kidney cells (lacks carrier protein)Remains in urine, and crystalizes.-Concept 7.4: Active TransportMove against diffusion, needs energy.-Active energyActive transport uses ATP, not spontaneous, + Delta G.Preformed by carrier proteins.Sodium Potassium Pump: Terminal phosphate to carrier protein.-How ion pumps maintain membrane potentialVoltage difference is created by differences in the distribution of positive and negative ions across a membrane.Electrogenic pump: transport protein that generates voltage across membrane and stores energy that can be tapped for cellular work.Sodium potassium pump.Proton pump, used by fungi, plants and bacteria.Co-Transport: Active transport of a solute indirectly transports another.-ExocytosisTransport vesicles migrate to the membrane, fuse with it, and release theircontents.Moves out large number of molecules.Many secretory cells use exocytosis to export their products.Hormone secreting cells, enzymes from cells of the digestive tract. -EndocytosisCell takes in macromolecules by forming vesicles from the plasma membrane.3 TypesPhagocytosis (Cellular Eating)Pinocytosis (Cellular Drinking)Receptor-Mediated endocytosisPhagocytosis: cell engulfs a particle in a vacuole.Vacuole fuses with lysosomes to digest the particle.Filled with digestive enzyme used to destroy the particle.Pinocytosis: Cell drinking.Receptor-Mediated endocytosis, binding of ligands to receptors triggers vesicle formation.A ligand is any molecule that binds specifically to a receptor site.Ex: Human cells use receptor-mediated endocytosis to take in cholesterol.Hypercholesterolemia: inherited disease where LDL receptors are defective, cholesterol is not taken into the cells leads to atherosclerosis-OsmosisDiffusion of H2O across a selectively permeable membraneWater moves from high to low solute concentration till its equal.2 solutions of Na Cl one is .5M, the other is 2.5M. if a water permeable membrane separates the two solutions, water will move from the .5M solution to the 2.5M solution till equilibrium is reached.-Water Balance of CellsTonicity: Ability of a surrounding solution to cause a cell to gain or lose water.The membrane has an effect on Tonicity.Isotonic Solution: Solute outside the cell is same as in the cell.Hypertonic Solution: Cell loses water; Cell shrivelsHypotonic Solution: Cell gains water; Cell expands.Hypertonic Solutions and Hypotonic Solutions create osmotic problems forcells.Osmotic Regulation: Control of solute and water concentrations.Protist Paramecium: Hypertonic compared to its pond environment, has a contractile vacuole that acts as a pump.Cell wall helps maintain water balance.Plant cell in hypotonic solutions swell till the walls are turgid, in a hypertonic solution becomes flaccid, this can lead to an effect called plasmolysis.-Concept 7.1 Cellular membranes are fluid mosaics of lipids and proteins.Phospholipids are the most abundant lipid in the plasma membrane. Amphipathic Molecules are phospholipid containing a hydrophobic regionand hydrophilic region.Fluid mosaic Model: Membrane is a fluid structure with a mosaic of variousproteins and lipids.-Membrane Models1915: Membranes from red blood cells (erythrocytes) were analyzed and composed of phospholipids and proteins.1925: Garter and Grendel reasoned that the membrane is composed of a phospholipid bilayer.1935: Hugher Davison and James Derrick proposed a sandwich model in which the phospholipid bilayer lies between two globular proteins.1972: S. J. Singer and G. Nicolson proposed that the membrane is a mosaic of proteins dispersed within a lipid bilayer.Freeze Fracture studies of the plasma membrane supported the fluid mosaic model.Splice the membrane along the middle of the phospholipid bilayer. -Fluidity of MembranesPhospholipids in the plasma membrane can move within the bilayer, such as across or even flip with one on the opposite side of the bilayer.As temperatures cool, membranes move from fluid to solid, the lipids determine the temperature that solidifies
View Full Document
Unlocking...