membranes membrane functions basic structure membrane functions chapter 11-12

Transcription

1 membranes chapter - membrane functions Ca + hormone IP H + HO compartmentalization intracellular compartments scaffold for biochemical activities organize enzymes selectively permeable membrane allows control of movement of substances ADP membrane functions 6 5 hormone IP Ca + ADP H HO transporting solutes facilitate the movement of substances between compartments external signalling receptors respond to stimuli intracellular interaction recognize and interact with cells energy transduction photosynthesis respiration basic structure trilaminar appearance phospholipid bilayer proteins interspersed 50 nm

2 lipid bilayer fluid-mosaic model glycoprotein oligosaccharide glycolipid membrane composition lipid components bound to proteins by non-covalent bonds hydrophobic interactions movement amphipathic lipids phosphoglycerides sphingolipids cholesterol in animals phospholipids cholesterol smaller lipid less amphipathic only found in animals sterol fluidity hinders movement of lipids fluidity liquid layer phospholipids move lateral shift transverse diffusion liquid-crystal or gel depends on temp depends on lipids D fluid selective rearrangement ER - addition of new PL scramblases

3 fluidity structure depends on temperature tightly packed lipids become more solid altering lipid structure affects fluidity trans- cis- 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 movement fusion division chemical composition asymmetry of membrane lipids inner and outer membranes have different lipids phosphatidylcholine membrane carbohydrates oligosaccharide glycolipid glycoprotein

4 membrane proteins integral proteins amphipathic hydrophilic hydrophobic membrane proteins peripheral proteins completely outside membrane attached by weak bonds membrane proteins lipid-anchored proteins (Glycophosphatidylinositol) GPI-linked proteins inner-leaflet proteins protein movements control of protein mobility proteins move slowly limited by cytoskeleton other proteins extracellular materials copyright 0 Pearson Education, Inc.

5 distribution of proteins membrane domains / cell polarity epithelia apical membrane lateral membrane basal membrane transport / permeability net flux difference in influx and efflux transport mechanisms passive active non-mediated transporter mediated O glucose ADP + P O glucose transport / permeability diffusion requires permeability electrochemical / concentration gradient osmosis diffusion of water water crosses plasma membrane quickly aquaporins passive active non-mediated transporter mediated O glucose O glucose ADP + P hypotonic hypertonic isotonic

6 osmosis plant cells osmosis hyperosmotic -- plasmolysis hypoosmotic -- turgid Water moves from high water to low water pure water --> ψ = 0 solutes --> negative pressure --> positive negative pressure? diffusion of ions ion channels selective bidirectional diffusion can be gated or ungated gated-channels voltage-gated potassium channels potassium channels potassium channels Eukaryotic KV channels 6 membrane-associated helices pore domain voltage-sensing domain S4 Eukaryotic KV channels 6 membrane-associated helices pore domain voltage-sensing domain outside cell S S S S4 S5 P S6 voltage-sensing cytosol pore REST (closed) OPEN INACTIVATED

7 glucose facilitated diffusion passive specific saturable regulated active transport sodium-potassium pump major electrogenic pump membrane bound enzyme E conformation E conformation high low low high copyright 0 Pearson Education, Inc. active transport proton pumps H + ase main electrogenic pump for plants, fungi, bacteria active transport H + / ase controls production of stomach acid H O + CO Soil particle Ca Ca + + Mg + H CO HCO + H + H + gastic pits pepsinogen HCl pepsin Root hair Cell wall parietal cell chief cell H + Cl - copyright 0 Pearson Education, Inc. copyright 0 Pearson Education, Inc.

8 coupling transport co-transport also called secondary gated channels most channels are gated - mechanical, chemical, voltage Mimosa pudica transport indirect use of can be symport or antiport neurons cell body dendrites axon resting Nernst equation [ion] outside Eion = RT / zf (log [ion] inside ) EK = -90 mv actual resting (around -70mV) graded s - relative to stimulus hyperpolarization depolarization usually caused by Na+ influx schwann cell axon axon myelin sheath myelin sheath axon hillock

9 Membrane (mv) action all or none +50 Key Action RISING PHASE 4 all sodium channels open REPOLARIZATION inactivation gates close impulse propagation refractory period saltatory conduction nodes of ranvier Action Axon Plasma membrane Cytosol 0 50 Threshold 4 Action 5 Resting DEPOLARIZATION some sodium channels open 00 Time Extracellular fluid Sodium channel Potassium channel Plasma membrane Action Cytosol Inactivation loop 5 UNDERSHOOT RESTING STATE synapses Electrical Synapses Chemical Synapses Postsynaptic chemically-gated channels neurotransmitters bind with receptors on postsynaptic cell different types of receptors - different cells eliminated by enzymes and reuptake