Fluid Mosaic ModelPhospholipids form a bilayer which is like a“lake” in which a variety of proteins “float.”
Phospholipids BilayerForms Spontaneously in waterVary in fatty acid chain length, degree of saturation, and phosphategroupsMembranes may be up to 25 percent cholesterolFlexible allowing lateral movementof moleculesFluidity depends on temperatureand lipid composition.
Components of the Fluid Mosaic Model• Lipids – Phospholipids/ Cholesterol• Proteins – Intergral – Peripheral• Carbohydrates
Membrane Bounds ProteinsTwo types of membrane proteins:• Peripheral membrane proteins lack exposed hydrophobic groups and do not penetrate the bilayer.• Integral membrane proteins have hydrophobic and hydrophilic regions or domains.
Transmembrane Proteins• Type of integral protein• Extend all the way through the phospholipid bilayer.
Selective PermeabilitySome substances can Passive transport:pass through, but not no outside energyothers required (diffusion).What can pass:- Small Active transport:- Uncharged energy requiredExamples?
DiffusionThe process ofrandom movementtoward equilibriumIt is the net movementfrom regions ofgreater concentrationto regions of lesserconcentration.
What Controls the Speed of Diffusion?- Diameter of the molecules or ions- Temperature of the solution- Concentration Gradient- Electrochemical Gradient- When a cell is involved you also have to consider movement across a membrane.
Simple DiffusionSmall molecules pass directly throughthe lipid bilayer.Water and lipid-soluble molecules candiffuse across the membrane.Electrically charged and polar moleculescan NOT pass through easily.
OsmosisThe Diffusion of WaterOsmosis depends on the number ofsolute particles present, not the type ofparticles.
Hypertonic Solutions: High Solute Concentrations Cell Shrinks
Hypotonic Solutions: Low Solute Concentrations Cell Lyses in Animal CellsSwells in Plant Cells (Turgor Pressure)
Isotonic Solutions: Equalsolute/water concentration Cell Remains the Same
Facilitated DiffusionPassive Transport across a membrane usingan integral membrane proteinChannel proteins: have a central pore linedwith polar amino acids.Carrier proteins: membrane proteins that bindsome substances and speed their diffusionthrough the bilayer.
Channel ProteinsSpecificityBest Example areIon ChannelsMost are “Gated”Ligand-Gated Rate and direction of ion movement through channels depends on the concentration gradient and the distribution of electrical charge.Voltage Gated
Membrane PotentialA charge imbalance across a membrane.Represents lots of potential energySignals volatge-gated channels to openCritical to ATP production during CellularRespiration or Photosynthesis
Carrier ProteinsPassive TransportDirectly binds to moleculeThen Changes shape to move the molecule across the membrane
Active TransportRequire EnergyMove moleculesAGAINST theconcentration gradientUniportersSymportersAntiporters
Large Molecule TransportEndocytosis: bring Exocytosis: Movematerial into the cell material out of the cellusing vesicles using vesicles