membranes chapter 11-1 1 cellular membranes 3 compartmentalization intracellular compartments 1. receiving info membrane receptors recognition and interaction with other cells. import and export of molecules movement of molecules between compartments intracellular compartments 3. capacity for movement and expansion changes in membrane shape addition of membrane basic structure trilaminar appearance phospholipid bilayer proteins interspersed basic structure fluid-mosaic model D fluid of lipid and protein ECM 50 nm CYTOPLASM
lipid composition lipid components bound to proteins by non-covalent bonds hydrophobic interactions movement amphipathic lipids phosphoglycerides phosphatidylcholine sphingomyelin glycolipids cholesterol in animals choline phosphate glycerol fatty acids loxoscelism action of venoms Loxosceles sp. sphingomyelinase-d acts on sphingolipids sphingomyelin fluidity liquid layer phospholipids move flex/rotate lateral shift transverse diffusion flip-flop liquidity depends on temp depends on lipids cholesterol smaller lipid sterol less amphipathic only found in animals fluidity low temps (maintains fluidity) prevents packing higher temps (reduces fluidity) hinders movement of lipids
membrane fluidity factors for fluidity tail length unsaturated vs. saturated cholesterol temperature/pressure trans- cis- adding lipids selective rearrangement ER - addition of new PL various enzymes add phospolipids scramblases (energy independent flippases) randomly distribute phospholipids Golgi - flippases - flip specific phospholipids to cytosolic side maintains assymmetry chemical composition asymmetry of membrane lipids inner and outer membranes have different lipids phosphatidylcholine membrane carbohydrates - glycocalyx glycoprotein oligosaccharide glycolipid fluidity Lipid rafts Outer layer contains specialized regions Cholesterol and sphingolipids pack together form highly ordered microdomains lipid rafts cell-surface receptors GPI-anchored proteins
dynamic properties self-sealing dynamic properties movement fusion division intregral proteins transmembrane proteins amphipathic hydrophilic hydrophobic monolayer-associated α-helix attach with only to inner leaflet by an α- helix integral proteins lipid-anchored proteins (Glycophosphatidylinositol) GPI-linked proteins inner-leaflet proteins peripheral proteins protein-attached completely outside membrane attached by weak bonds
protein movements control of protein mobility proteins move slowly limited by cytoskeleton other proteins extracellular materials distribution of proteins membrane domains / cell polarity epithelia apical membrane lateral membrane basal membrane copyright 01 Pearson Education, Inc. proteins membrane protein functions tranporters ion channels anchors receptors enzymes transport / permeability SMALL NON- POLAR SMALL POLAR MOLECULES O, CO, N, NO, etc. HO, ethanol, glycerol, etc. EASILY FAIRLY EASILY net flux difference in influx and efflux what can move across lipid bilayer?? polarity size charge LARGE POLAR MOLECULES amino acids, glucose, nucleosides VERY SLOWLY IONS H +, Na +, Ca +, K +, Cl -, HCO3 - BLOCKED
transport / permeability transport / permeability membrane transport proteins channels - passive transporters diffusion channels channelmediated transportermediated transporters energy plasma membrane concentration gradients transport mechanisms diffusion requires requires permeability and gradient ions -> electrochemical gradient uncharged solutes -> concentration gradient active transport against gradient uses ATP plasma membrane PASSIVE ACTIVE concentration gradients PASSIVE ACTIVE diffusion channelmediated transportermediated energy transporters active transport facilitated diffusion passive specific saturable regulated transmembrane pumps coupled pumps ATP-driven pumps Light-driven pumps ATPASE electrochemical gradients COUPLED PUMP LIGHT-DRIVEN PUMP
coupling transport co-transport also called secondary transport indirect use of ATP can be symport or antiport UNIPORT SYMPORT ANTIPORT pumps ATP-driven pumps (transport ATPases) P-type directly phosporylated pump ions ABC transporters (ATP-binding cassette) ATPase domains pump small molecules V-type (vacuolar) hydrolyze ATP pump protons COUPLED TRANSPORT active transport sodium-potassium pump major electrogenic pump membrane bound enzyme 3 Na + active transport proton pumps H + ATPase main electrogenic pump for plants, fungi, bacteria E1 conformation E conformation Ca+ Soil particle Mg+ Ca+ high Na + low K + Na + K + ATP low Na + high K + K + copyright 01 Pearson Education, Inc. H O + CO H CO 3 Root hair HCO + 3 Cell wall H+ H+ copyright 01 Pearson Education, Inc.
active transport H + /K + ATPase controls production of stomach acid gastic pits pepsinogen HCl pepsin osmosis diffusion of water water crosses plasma membrane quickly aquaporins clusters of 4 monomers only conduct water hyperosmotic hypoosmotic isoosmotic parietal cell chief cell H + Cl - copyright 01 Pearson Education, Inc. osmosis contractile vacuoles plant cells osmosis hyperosmotic -- plasmolysis hypoosmotic -- turgid Water potential moves from high water potential to low water potential pure water --> ψ = 0 solutes --> negative pressure --> positive negative pressure? protozoans contractile vacuoles diffusion of ions ion channels selective bidirectional diffusion can be gated or ungated most are ungated gated-channels voltage-gated ligand-gated (chemically gated) mechanically-gated
potassium channels potassium channels KV channels 6 membrane-associated helices pore domain voltage-sensing domain Eukaryotic KV channels 4 subunits 6 membrane-associated helices pore domain voltage-sensing domain S4 outside cell S6 pore cytosol N P vertebrate KV channel REST (closed) OPEN INACTIVATED membrane potential membrane potential gated channels can convey signals mechanically and voltage-gated channels Mimosa pudica neurons cell body dendrites axon schwann cell axon axon myelin sheath axon hillock myelin sheath S5 S1 S S3 S4 voltage-sensing
Membrane potential (mv) membrane potential resting potential Nernst equation (calculates equilibrium potential) [ion] outside Eion = RT / zf (log ) [ion] inside EK = -90 mv actual resting potential (around -70mV) graded potentials - relative to stimulus hyperpolarization depolarization usually caused by Na + influx membrane potential action potential all or none Extracellular fluid +50 0 50 100 Key Action potential Threshold Time 1 Na + 3 RISING PHASE 4 DEPOLARIZATION all sodium channels open some sodium channels open Sodium channel Potassium channel K + Resting potential 3 4 5 1 REPOLARIZATION inactivation gates close Plasma membrane Cytosol Inactivation loop 5 UNDERSHOOT 1 RESTING STATE axons membrane potential impulse propagation refractory period saltatory conduction nodes of ranvier 1 Action potential Axon Plasma membrane synapses Electrical Synapses Chemical Synapses Postsynaptic chemically-gated channels Na+ Cytosol Action potential Na+ 3 Action potential Na+
membrane potential neurotransmitters bind with receptors on postsynaptic cell different types of receptors - different cells eliminated by enzymes and reuptake