Movement into Cells Human Biology Lecture 2 2024 PDF

Movement into Cells Human Biology Lecture 2 2024 Philip Poronnik Payne Scott Distinguished Professor School of Medical Sciences Faculty of Medicine and Health The story so far… we have learned that the cell is in effect a self contained ecosystem… But how does “stuff” get in and out ? The balloon is...

Movement into Cells Human Biology Lecture 2 2024 Philip Poronnik Payne Scott Distinguished Professor School of Medical Sciences Faculty of Medicine and Health The story so far… we have learned that the cell is in effect a self contained ecosystem… But how does “stuff” get in and out ? The balloon is a phospholipid bilayer… The plasma membrane Hydrophobic - Hydrophilic Caroline Giardina Lipid bilayers are impermeable to most essential molecules and ions Permeable to water molecules and a few other small, uncharged, molecules like oxygen and carbon dioxide. Lipid bilayers are NOT permeable to: ions such as K+, Na+, Ca2+, Cl-, HCO3 small hydrophilic molecules like glucose macromolecules like proteins and RNA Movement of molecules DIFFUSION: with time – due to random motion molecules become equally distributed i.e. to eliminate concentration gradients e.g. ink drop in water Osmosis - Water also diffuses The more solute (ie sugar or salt) in a given volume the higher the concentration of salt and the lower amount of water Water will always flow to where its concentration is lower Bulk flow of water through a semipermeable membrane into another aqueous compartment containing solute at a higher concentration (osmosis definition) Water wants to at equilibrium… same number of molecules in each compartment Remember - plasma membrane is SEMIpermeable!! TONICITY – osmotic pressure gradient A B C 1 M glucose 1 M lactose 0.1 M glucose 180g/l 342 g/l 18.0 g/l 180 g of glucose in ONE litre = 1M A:B = ISOtonic C:A/B = HYPOtonic A/B:C = HYPERtonic 3 times more sucrose molecules so LESS water molecules Water molecules move to equal the amount… 1 M sucrose 0.3 M sucrose Membrane Membranesemipermeable impermeable BUT Cell membranes are non-rigid… OSMOSIS = SALT SUCKS…. Red Blood Cells hypotonic 50 isotonic 300 hypertonic 500 mosmol https://sciencephotogallery.com/featured/1-red-blood-cells-in-the-rouleau-formation-dennis-kunkel-microscopyscience-photo-library.html Ion Transport OK – so now we get it !! This balloon stuff and dribs ands drabs of water And gas getting across – but what about the rest ?? https://phys.org/news/2021-03-mechanism-cellular-ion-channels.html Cell membrane contains “transmembrane” proteins / integral membrane proteins Some of these form pores through the membrane two broad categories 1. Channels – facilitated diffusion 2. Transporters – facilitated diffusion or active transport Ions and nutrients can move through these pores Glycine receptor Chloride channel Hyperekplexia Strychnine https://www.youtube.com/watch?v=nEJNmGHz4Gg Remember all that water in the gut and kidney ? Aquaporins - water channels Peter Agre – Nobel Prize for Chemistry 2004 Facilitated Diffusion Active transport ATP ATP Passive = DOWN a concentration gradient Active = AGAINST a concentration gradient Rate of movement through the pore Pores, channels SATURATE!!! Diabetes glucose ?? Concentration of Ion Ion channels CONDUCT charge!!! + + ++ + + + + + + + + + + + + + + + + + + + + + + + Electrochemical potential difference The Nobel Prize in Physiology or Medicine 1991 "for their discoveries concerning the function of single ion channels in cells Patch-clamping – Single Ion Channel Recording What are the ion concentrations outside the cell? We know from blood… So what about inside ?? Active Transport: Ubiquitous Sodium-Potassium Pump 140 mM 5 mM Na+ high Na+ low K+ low K+ high 10 mM 150 mM AKA – Na-K ATPase The Sodium Pump Sodium-Potassium Pump http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/eustruct/sppump.html Consequences of Na-K ATPase action Opposite movement of key ions Unequal movement of charge 3+ (NA) out and only 2+ (K) in ALL CELLS HAVE A NEGATIVE MEMBRANE POTENTIAL This is the electrochemical driving force!!! the relative contribution of any given ion is determined not only by its concentration gradient across the plasma membrane, but also by its relative membrane permeability https://www.cambridge.org/core/books/abs/basic-physiology-for-anaesthetists/nerve-actionpotential-and-propagation/31B6C11A49B20CC69D3EB1E5CCCFB208 Facilitated Diffusion Regulated movement of nutrients across the membrane Glucose Amino acids Often use Na+ gradient as driving force The Cell Getting In and Out The Ins and Outs Endocytosis Exocytosis Clathrin (receptor) Mediated Endocytosis CME is heavily implicated in nutrient uptake, signal transduction, synaptic vesicle recycling, maintenance of cell polarity, and antigen presentation Exocytosis Phagocytosis (engulfing particles) https://www.youtube.com/watch?v=ZKE8qK9UCrU https://www.youtube.com/watch?v=jaKQRRbkwds https://www.youtube.com/watch?v=YfQqrvTVI58 https://www.youtube.com/watch?v=Dl1ufW3cj4g https://www.youtube.com/watch?v=5DGwOJXSxqg&t=17s PLEASE WATCH!! Learning Objectives Explain how a single cell can survive and function in isolation. Distinguish the main structures and functions of a cell and its main organelles. Explain how cell membranes create compartmentalisation which regulate the flow of substances into and out of cells. Describe the passive diffusion of water across semi- permeable cell membranes and the role of aquaporins Describe how the cell uses the Na-K ATPase to create the electrochemical gradient that provides the energy for life Explain how larger molecules and particles get in and out of cells