Cell membrane lecture.pptx

Life Sciences Membrane, Transporters, and Osmosis Dr Ramin Farahani School of Medical Sciences Acknowledgments Dr Belal Chami The University of Sydney Page 1  Learning Objectives – List the functions of biological membranes – Differentiate the different classes of membrane transport proteins...

Life Sciences Membrane, Transporters, and Osmosis Dr Ramin Farahani School of Medical Sciences Acknowledgments Dr Belal Chami The University of Sydney Page 1  Learning Objectives – List the functions of biological membranes – Differentiate the different classes of membrane transport proteins – Explain fluid balance and osmosis – Define isotonic/hypotonic/hypertonic solutions The University of Page Sydney 2  Fluid balance The University of Page Sydney 3  Body fluid balance and distribution Movement of water in body needs to be controlled Swelling Dehydration The University of Page Sydney 4  Biological Membranes – barrier for water movement A barrier between the inner and outer surface Boundaries among organelles / inner compartments Control the movement of substances into and out of cells Regulate the composition within individual cells Control the flow of information between cells (recognizing or sending signals) Capture and release energy (e.g. mitochondria) Cell adhesion Synthesize steroids etc. The University of Page Sydney 5  Structure and Function of Plasma Membrane Bi-layer: 2 layers of phospholipids Phosphate group (head) + 2 chains of fatty acids (lipid tails) Head = hydrophilic (water loving); Tail = hydrophobic (water fearing) Amphipathic Allow cell to interact with watery environment but remain water resistant Selective permeability – some molecules are allowed in while others are kept out Permeable to lipid-soluble substances (e.g. O2) Impermeable to charged molecules (e.g. ions) The University of Page Sydney 6 6  Body fluid compartments - Intracellular fluid ~25 L Plasma membrane - Interstitial fluid ~ 12 L Blood vessel - Plasma ~ 3 L - Extracellular fluid ECF = plasma + interstitial fluid The University of Page 7 Sydney  Water movement and osmosis – Osmosis: Water moves through a semi-permeable membrane – Passive transport to equalize the concentration of a solution – Osmotic pressure OP – Created by a concentration difference of dissolved substances between two sides of a bio- membrane – Hydrostatic pressure – Movement of water stops – The size of the solute particles does not influence osmosis – Equilibrium is reached once sufficient water has moved to equalize the solute The University of Page 8 concentration on both sides Sydney  Movement across biological membranes – Passive movement – Follow the concentration gradient – Does not require energy – Driving forces: Concentration gradient – diffusion / facilitated diffusion Electrical potential – only for charged particles – Active transport – Against the concentration gradient – Require energy – Endocytosis, exocytosis The University of Page 9 Sydney  Diffusion and facilitated diffusion – Diffusion: Passive movement across membranes – Movement of solute to form equilibrium – Facilitated diffusion: diffusion for substances that cannot cross lipid bi-layer due to size/charge/polarity – Movement is still down a concentration gradient – Carrier proteins The University of Page Sydney 10  Membrane Proteins – Transport proteins – Enzymes – Intercellular junctions – Cell-cell recognition – Receptors – Adhesion to extracellular matrix The University of Page Sydney 11  Membrane Transport Proteins Channels – Membrane proteins that allow passive movement of solutes through membrane down their concentration gradient – Ions (ion channels) – Water (aquaporins) – Specific or nonselective – Gated: open or closed in response to local changes – Ligand-gated: signal molecule, can be external (e.g. neurotransmitter, hormone) or internal (Ca2+, cAMP, lipids etc.) – Voltage-gated: alterations in membrane potentials The University of Page – Mechanical stretch (cell movement) Sydney 12 1  Aquapor ins – Small, integral membrane proteins – Expressed throughout the animal and plant kingdoms – Form pores that allow passage movement of water by osmosis – Plumbing system for cells Peter Agre 2003 Nobel Prize The University of Page Sydney 13  Membrane Transport Proteins Pumps – Active transport, against concentration gradient – Catalyse the hydrolysis of ATP to ADP – Use energy – E.g. Na+/K+-ATPase (move 3 Na+ out and 2 K+ into the cell) and electrolyte balances – Important for controlling movement of water – concentration gradient The University of Page Sydney 14  Membrane Transport Proteins Carriers/Transporters – Facilitated diffusion or active transport – Bind specific molecule and then transfer it across the membrane – Protein conformation changes – The affinity of binding site for the bound substance changes – Three groups: Uniporter: only one substance Symporter: binding of more than one Antiporter: exchange Co-transport The University of Page Sydney 15  Cellular Transport Exocytosis – Exo – Out; Cyto – cell; sis – state, process, action – Vesicles containing material for export – Waste removal – Secrete hormones The University of Page Sydney 16  Cellular Transport Endocytosis – Endo – In – The reverse of exocytosis – Take in material – White blood cell engulfing bacteria/viruses The University of Page Sydney 17  Water imbalance - oedema – Accumulation of excess water in the tissues – Water leakage from capillaries The University of Page Sydney 18  Intravenous fluid therapy – Maintain the body fluid and electrolytes balance – Various types of fluid – purpose The University of Page Sydney 19  Osmo sis Isotonicity – Iso – equal, same; Tonos - streching – Concentration of dissolved substances is the same in solution as in the cell – The same OP for both sides – Isotonic solution of animal cells – a 0.9% w/v NaCl solution (saline) – body fluids – Most IV therapy solutions The University of Page Sydney 20  Osmo sis Hypotonicity – Hypo – under, below – Outside solution has lower OP (less solute) than cell interior – Water moves into cell – 0.45% saline – true dehydration (lost water only, without losing any electrolytes) The University of Page Sydney 21  Osmo sis Hypertonicity – Hyper – above – Outside solution has higher OP (more solute) than cell interior – Water moves out of cell – 3% Saline – Hyponatraemia (low sodium) – Patients who need electrolytes but are already on fluid overload (i.e. heart failure, severe oedema) The University of Page Sydney 22 Osmosis and I.V. therapy Q: What would happen if pure water was given via I.V.?  Re-cap questions – What is the basic structure of all biomembranes? – Can you list the functions of plasma membrane? – How it maintains discrete extracellular fluid and intracellular fluid composition and cell volume? The University of Page Sydney 24