MembranesMembranes

What is the relationship between What is the relationship between the mosaic structure of the cell the mosaic structure of the cell membrane and it’s function?membrane and it’s function?

Osmosis and diffusion effects on biological Osmosis and diffusion effects on biological organismsorganisms

Integral proteinIntegral protein CholesterolCholesterol Cell to cell communicationCell to cell communication Active/passive transportActive/passive transport Exocytosis/ endocytosisExocytosis/ endocytosis

Cell membraneCell membrane

Happened early in evolution.Happened early in evolution. Separate cell from its surroundingsSeparate cell from its surroundings Selective permeability: allows only certain Selective permeability: allows only certain

things to crossthings to cross

Cell membranesCell membranes

Membranes: fluid mosaics of lipids and Membranes: fluid mosaics of lipids and proteinsproteins

Amphipathic molecule: phospholipids have Amphipathic molecule: phospholipids have both a hydrophilic (head) and hydrophobic both a hydrophilic (head) and hydrophobic (tail) region also membrane proteins(tail) region also membrane proteins

Hydrophobic portions are hidden in the Hydrophobic portions are hidden in the middle of the bilayer membranemiddle of the bilayer membrane

Lateral movementLateral movement

Proteins and lipids can move laterally within Proteins and lipids can move laterally within the membranethe membrane

Seem to move with specific Seem to move with specific direction….driven along cytoskeletal fibers direction….driven along cytoskeletal fibers by motor proteins.by motor proteins.

Membranes must be fluid to work properly.Membranes must be fluid to work properly. Salad oilSalad oil Cholesterol hinders closeness of the Cholesterol hinders closeness of the

phospholipids making membrane slightly phospholipids making membrane slightly less fluid but maintaining fluidness into lower less fluid but maintaining fluidness into lower temperatures.temperatures.

Membranes differMembranes differ

Membranes with different functions differ in Membranes with different functions differ in their makeup.their makeup.

Mitochondria have more embedded proteinsMitochondria have more embedded proteins

Membrane transportMembrane transport

Hydrophobic not charge can dissolve + Hydrophobic not charge can dissolve + partially crosspartially cross

Hydrophilic: more difficultHydrophilic: more difficult

Cell Wall: plantsCell Wall: plants

Cell wall: Cell wall: – CelluloseCellulose– ProteinsProteins– PolysaccharidesPolysaccharides– Pectin (starch)Pectin (starch)

Cell MembraneCell Membrane

Cell Membrane (animal)Cell Membrane (animal)– Phospholipid bilayerPhospholipid bilayer– Imbedded proteins: protein channelsImbedded proteins: protein channels– CholesterolCholesterol– Glycoproteins: cell to cell recognitionGlycoproteins: cell to cell recognition

Membrane transportMembrane transport

Hydrophobic: no charge, non polarHydrophobic: no charge, non polar If small: CO2, O2 can dissolve and cross If small: CO2, O2 can dissolve and cross

easilyeasily

Hydrophilic: polar: more difficult H2O, Hydrophilic: polar: more difficult H2O, glucoseglucose

Passive transportPassive transport

Passive transport = diffusion, osmosis, Passive transport = diffusion, osmosis, facilitated diffusion (uses transport protein)facilitated diffusion (uses transport protein)

Diffusion = tendency of molecules to spread Diffusion = tendency of molecules to spread out due to their kinetic energy.out due to their kinetic energy.

Substances will diffuse down their Substances will diffuse down their concentration gradient concentration gradient

Unaffected by the concentration of other Unaffected by the concentration of other substances.substances.

Membrane transport: FacilitatedMembrane transport: Facilitated

Facilitated diffusion: H2O, glucoseFacilitated diffusion: H2O, glucose Transport Proteins: may be hydrophilic Transport Proteins: may be hydrophilic

insideinside Carrier: may physically move substrateCarrier: may physically move substrate Aquaporins: for H2OAquaporins: for H2O May be substrate specific or may just span May be substrate specific or may just span

the membranethe membrane

Membrane Transport: facilitatedMembrane Transport: facilitated

Transport protein:Transport protein:– Protein channel: Protein channel:

Ion channels usually gated. Need chemical or Ion channels usually gated. Need chemical or electrical stimuluselectrical stimulus

– Protein carrierProtein carrier

OsmosisOsmosis

Osmosis = diffusion of water: passiveOsmosis = diffusion of water: passive Water down its Water down its concentration gradientconcentration gradient Hypotonic to HypertonicHypotonic to Hypertonic

less solute(more water) less solute(more water) more solute more solute

Cell wall: lets in only so much water until cell Cell wall: lets in only so much water until cell is turgid (healthy for plant)is turgid (healthy for plant)

Animal cell with no wall will burst if put in Animal cell with no wall will burst if put in hypotonic solution.hypotonic solution.

Active transportActive transport

Sodium – potassium pumpSodium – potassium pump Pumping solutes against their concentration Pumping solutes against their concentration

gradient.gradient. Cell: inside K+ high Na+ lowCell: inside K+ high Na+ low Must use energy to maintain this balanceMust use energy to maintain this balance ATP: phos. Group might bind directly to the ATP: phos. Group might bind directly to the

transport protein transport protein

Na+ K+ pumpNa+ K+ pump

Na+ binds with protein: causes ATP to ADPNa+ binds with protein: causes ATP to ADP The added phosphate changes protein The added phosphate changes protein

shapeshape So, protein spits Na+ out the other side and So, protein spits Na+ out the other side and

grabs K+grabs K+ K+ binding releases the PhosphateK+ binding releases the Phosphate 3 Na+ out and 2 K+ in3 Na+ out and 2 K+ in

Voltage Voltage

Cell membrane have voltageCell membrane have voltage Membrane potential = electrical potential Membrane potential = electrical potential

energy due to the charges in and out of cell energy due to the charges in and out of cell ( - inside + outside)( - inside + outside)

Animal: electrogenic pump (Na+, K+)Animal: electrogenic pump (Na+, K+) Plants: use proton pumpPlants: use proton pump

2 forces drive diffusion2 forces drive diffusion Membrane potential = electrical energyMembrane potential = electrical energy Concentration gradient = chemical energyConcentration gradient = chemical energy

Cotransport Cotransport

Plant pumps H+ outPlant pumps H+ out When it diffuses back in it can carry sucrose When it diffuses back in it can carry sucrose

with it. (even against concentration gradient)with it. (even against concentration gradient)

ExocytosisExocytosis

Exocytosis: vesicle fuses with cell Exocytosis: vesicle fuses with cell membrane to release it secretions outsidemembrane to release it secretions outside

Endocytosis Endocytosis

Membrane forms vesicle with something Membrane forms vesicle with something from outsidefrom outside

1. phagocytosis: pseudopodium1. phagocytosis: pseudopodiumthen fuse with lysosomethen fuse with lysosome

2. pinocytosis: wrap around drop of 2. pinocytosis: wrap around drop of extracellular fluidextracellular fluid

3. receptor mediated: humans- cholesterol 3. receptor mediated: humans- cholesterol ligand: any molecule that binds to receptorligand: any molecule that binds to receptor