Test Yourself: Understanding Biophysics Concepts in Physiology

1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58

2. BIOPHYSICS By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology

3. Test Yourself • Which of the following best describe the process of diffusion : • a) A " downhill " process . • b) An " uphill " process . • c) A process by which only large molecular weight proteins may move across biological membrane . • d) require metabolic energy . • e) depends on the balance between hydrostatic pressure and oncotic pressure of plasma protein Biophysics , Abdelaziz Hussein

4. Intercellular Junctions

5. Tight Junctions Epithelium Lumen Basolateral border Luminal or apical border

6. Tight Junctions Basolateral membrane Apical membrane Tight Junctions

7. Leaky Tight Junctions Na H2O Na Lumen H2O Capillary

8. Tight Tight Junctions Na H2O Na Lumen H2O Capillary

9. Gap Junctions

11. Gap Junctions Lumen Capillary

12. Gap Junctions Impulse Impulse

13. Some Types of Ion Channels Biophysics , Abdelaziz Hussein

14. Types of Gated Ion Channels

15. 1. Ligand-gated or chemical-gated ion channels Ion Ligand Receptor Gate Biophysics , Abdelaziz Hussein

16. 1. Ligand-gated or chemical-gated ion channels Biophysics , Abdelaziz Hussein

17. 1. Ligand-gated or chemical-gated ion channels Biophysics , Abdelaziz Hussein

18. 1. Ligand-gated or chemical-gated ion channels Biophysics , Abdelaziz Hussein

19. 1. Ligand-gated or chemical-gated ion channels Def., • Channels are closely associated with a membrane receptors Mechanism: • When the chemical agent binds to its receptor, it causes a conformational change in the channel →open the channel Biophysics , Abdelaziz Hussein

20. 1. Ligand-gated or chemical-gated ion channels Selectivity: • nonselective ion channels i.e. conduct more than one type of similarly charged ions + + Biophysics , Abdelaziz Hussein

21. 1. Ligand-gated or chemical-gated ion channels Example: • Cholinergic receptor at the motor end plate of sk. Ms → permits the passage of Na into and K out of the ms cell • Important in generation of motor end plate potential Biophysics , Abdelaziz Hussein

23. 2. Voltage-gated ion channels Ion Gate Biophysics , Abdelaziz Hussein

24. 2. Voltage-gated ion channels + + + + + + + + + + + + + + ++_ + ++ + +++ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Biophysics , Abdelaziz Hussein

25. 2. Voltage-gated ion channels _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ + + + + + + + + + + + + + + ++_ + ++ + +++ Biophysics , Abdelaziz Hussein

26. 2. Voltage-gated ion channels _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ + + + + + + + + + + + + + + ++_ + ++ + +++ Biophysics , Abdelaziz Hussein

27. 2. Voltage-gated ion channels Def., • Channelsopen by changes in cell membrane potential Mechanism • When the membrane potential reach certain level→ triggers the movement of +vely charged amino-acids in the α- subunits which form the ion conducting shaft of the channel→ cause conformational change in the channel→ open it Biophysics , Abdelaziz Hussein

28. 2. Voltage-gated ion channels Biophysics , Abdelaziz Hussein

29. 2. Voltage-gated ion channels Selectivity: • ion selective channel i.e. conduct only one ion Example: • Voltage gated Na, K and Ca channels • Important in generation of action potential Biophysics , Abdelaziz Hussein

31. Facilitated Diffusion

32. Facilitated Diffusion Def • It is the diffusion of substances across the cell membrane (down electrochemical gradient) which needs the presence of carrier proteins→ carrier mediated diffusion. Biophysics , Abdelaziz Hussein

33. Facilitated Diffusion Mechanisms: • When the substance binds to its transport carrier protein→ it undergoes a reversible conformational change→ it transports the substance across the membrane downits concentration gradient. Biophysics , Abdelaziz Hussein

34. Facilitated Diffusion

35. Facilitated Diffusion Rate • Is limited because it depends on the availability of a definite No. of carrier proteins Characters • 1) It occurs down an electrochemical gradient • 2) It is passive i.e. no energy is required. • 3) It requires the presence of a transport carrier protein. Biophysics , Abdelaziz Hussein

36. Facilitated Diffusion Characters • 4) It is rate-limiting and saturable because it depends on the availability of a definite number of carrier or channel proteins Biophysics , Abdelaziz Hussein

37. Facilitated Diffusion Example: • Glucose transporters (GLUT) which transports glucose into RBCs, ms cells and adipose tissue Biophysics , Abdelaziz Hussein

38. Factors affecting Net Rate of Diffusion (Fick's law of diffusion)

39. Diffusion Fick’s Law of diffusion- M = Ds.A.DC x Adolph Fick 1829-1901 diffusion animation

40. Fick's law of diffusion • The important to the cell (for a substance diffuse in both directions) is not the total substance diffusing in both directions but the difference between these two (net rate of diffusion in one direction).

41. Fick's law of diffusion • Factors affecting net rate of diffusion • Concentration gradient for the solute. • Diffusion Coefficient or permeability coefficient of the membrane. • Membrane surface area. Rate of diffusion is directly proportional to these factors. 4. Membrane thickness or distance, the rate of diffusion is inversely proportional to the thickness of the membrane.

42. Fick's law of diffusion Fick's law: • D = diffusion coefficient. • A = area of membrane (cm2). • X = thickness of the membrane (cm). • C in and C out = the concentration of the material on the inside and outside of the membrane, respectively (mmol/L or mmol/cm3). • The -ve sign indicates that the material is moving down its concentration gradient

43. Active Transport

44. 2. Active Transport ATP Low concentration High concentration Biophysics , Abdelaziz Hussein

45. 2. Active Transport Def., Is the movement of substances across the cell membranes against an electrochemical gradient. Types: Abdelaziz Hussein

46. 2. Active Transport 1) Primary active transport → obtain its energy directly from the hydrolysis of ATP e.g. Na-K Pump, Ca ATPase, H-K ATPase 2) Secondary active transport → use the energy stored in the Na concentration gradient e.g.Na-glucose co-transport and Na-Ca exchange Abdelaziz Hussein

47. ADP • K+ = 4 mEq/L • Na+= 140 mEq/L ATP Na+ K+ • K+ = 140 mEq/L • Na+= 14mEq/L Na+ K+ ICF ECF High glucose Glucose Na+ Low Glucose Glucose Na+

49. 2. Active Transport • 2) Characters: • Occurs against the electrochemical gradient • Active i.e. energy is required. • Requires the presence of a transport carrier protein→ so exhibits; • Stereospecificity • Saturation • Competition • Rate limiting Abdelaziz Hussein

50. 2. Active Transport Abdelaziz Hussein