Membrane Dynamics: Movement and Potential

1. Membrane Dynamics: Movement and Potential

2. Mass Balance in the Body Intake Excretion (through intestine,lungs, skin) (by kidneys, liver,lungs, skin) BODYLOAD Metabolism toa new substance Metabolicproduction Law of Mass Balance Intake ormetabolicproduction Excretion ormetabolicremoval Existingbody load – + Mass balance =

3. Homeostasis

4. Homeostasis

5. Mass Balance and Homeostasis • Clearance • Rate at which a molecule disappears from the body • Mass flow = concentration  volume flow • Homeostasis  equilibrium • Osmotic equilibrium • Chemical disequilibrium • Electrical disequilibrium

6. Map of Membrane Transport

7. Diffusion • Diffusion is the net movement of particles from an area of higher particle concentration to an area of lower particle concentration. • Net movement = flux • Both the size and direction of movement is concentration-dependent.

8. Simple Diffusion Extracellular fluid Membrane surface area Concentration outside cell Molecular size Lipid solubility • Fick’s law of diffusion Concentration gradient Membrane thickness Composition of lipid layer Concentration inside cell Intracellular fluid Fick's Law of Diffusionsays: surface area • concentration gradient • membrane permeability Rate of diffusion membrane thickness Membrane permeability lipid solubility Membrane permeability molecular size Changing the composition of the lipid layer can increase or decrease membrane permeability.

9. Simple Diffusion

10. Two classes of compounds move by simple diffusion • Lipid soluble compounds • Small ions which move through protein channels a. channels are selective b. channels can be regulated

11. Membrane Transport Proteins

12. Channel Proteins: Gated • Usually closed • Often highly Selective (size, charge) • Chemical (e.g. intracellular messengers) • Temperature • Mechanical/tension • Electric (voltage) signals • Consist of subunits • Ion channels: e.g. K+, Na+, Ca2+ Leak channels open all time e.g. allow water, ions movement

13. Gating of Channel Proteins

14. Active Transport • Can transport against a concentration gradient • Requires energy input (ATP to ADP, P) • Two forms: • primary active transport • secondary active transport

16. Primary Active Transport 1 1 ECF ATP ADP ADP 5 2 3 Na+ from ICF bind ICF 2 K+ released into ICF ATPase is phosphorylated with Pi from ATP. Protein changes conformation. 3 Na+ released into ECF 2 K+ from ECF bind 4 3

17. Secondary Active Transport • Mechanism of the SGLT Transporter 1 Na+ binds to carrier. 3 Glucose binding changes carrier conformation. Intracellular fluid Lumen of intestine or kidney SGLT protein [Na+] low [glucose] high [Na+] high [glucose] low 4 Na+ released into cytosol. Glucose follows. 2 Na+binding creates a site for glucose.

18. Energy Transfer in Living Cells Glucose Energy is imported into the cell as energy stored in chemical bonds of nutrients such as glucose. Glucose Glycolysis ATP Pyruvate Metabolism The chemical bond energy is converted into high-energy bonds of ATP through the process of metabolism. Heat CA cycle H2O ETS CO2 Primary active transport Na+ The energy in the high-energy phosphate bond of ATP is used to move K+ and Na+ against their concentration gradients. This creates potential energy stored in the ion concentration gradients. ATP K+ ATP O2 ADP+Pi High [K+] Low [K+] Low [Na+] High [Na+] Secondary active transport Na+ K+ The energy of the Na+ gradient can be used to move other molecules across the cell membrane against their concentration gradients. 2 Cl– KEY CA cycle ETS = Citric acid cycle = Electron transport system

19. Membrane Transport Proteins

21. Carrier Proteins: Proteins are Required for Carrier-mediated Transport • Specificity • Saturation • Competition

22. Carrier-Mediated Transport Competition

23. Carrier-Mediated Transport Saturation

25. Phagocytosis: important in immune cells

26. Vesicular Transport

27. Polarized cell transporting epithelia

28. Transepithelial Transport of Glucose

29. Transcytosis

30. 46-61% body weight is water • How is water distributed in body?

31. Osmosis and Tonicity • Net diffusion of water from an area of low solute concentration to an area of higher solute concentration when movement of solute is prevented by a membrane.

33. Tonicity • Tonicity depends on the relative concentrations of nonpenetrating solutes

34. Osmolarity • Total number of osmotically active particles • Osmolarity = molar conc x # particles of solute in solution • (1 mM glucose) x 1 particle =1 mOs glucose • (1 mM NaCl) x 2 particles = 2 mOs NaCl

35. Tonicity • Describes only number of non-penetrating solutes 300 mM NaCl = 600 mOs NaCl Hypertonic solution Water moves out; cell shrinks 300 mOs Isotonic = same as cell; size stable Hypotonic = less than cell; cells lyse

36. NaCl, protein: non-penetrating • Urea: penetrating

37. The cell membrane enables separation of electrical charge in the body Resting membrane potential is the electrical gradient between ECF and ICF Resting membrane potential is the electrical gradient between ECF and ICF

39. Resting Membrane Potential Intracellular fluid -70 mV Extracellular fluid 0 mV

40. Terminology associated with changes in membrane potential

41. Equilibrium Potential • Nernst EquationEion = 61 x log [ion]out z [ion]in Z is electrical charge on ion • E for K+ = -90 mV • E for Na+ = +60 mV

43. Tonicity Problems RBC in a solution, what will happen to the cell? • 300 mOs NaCl ? • 300 mOs NaCl + 100 mOs urea? • 300 mOs NaCl + 100 mOs protein? • 300 mOs NaCl + 300 mOs urea?

44. Kidney Dialysis urea NaCl, proteins NaCl, proteins urea urea

45. Movement across Membranes