بسم الله الرحمن الرحيم

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 Member of American Society of Physiology

3. Test Yourself which of the following compartments, Na+ ions have the lowest concentration? • Interstitial fluid. • Plasma. • Intracellular fluid. • Lymph. Biophysics , Abdelaziz Hussein

4. Test Yourself Which mechanism is the main regulator of water intake? • Changes in ECF PH. • Urine formation. • Small changes in ECF volume. • Thirst. Biophysics , Abdelaziz Hussein

5. Test Yourself Cell membrane : • Consists almostly of protein . • Consists almostly of fat . • Is non selectively permeable membrane • None of the above. Biophysics , Abdelaziz Hussein

6. Test Yourself • The gap junction : • are absent in cardiac muscle . • are present but of little functional importance in cardiac muscle . • are absent in smooth muscle . • none of the above is might . Biophysics , Abdelaziz Hussein

7. Transport through the Cell Membrane Biophysics , Abdelaziz Hussein

8. Transport through the Cell Membrane Biophysics , Abdelaziz Hussein

9. 1. Passive Transport (diffusion) Low concentration High concentration Biophysics , Abdelaziz Hussein

10. 1. Passive Transport (diffusion) • Def. • It is movement of substances across the cell membrane down its electrochemical gradient. Biophysics , Abdelaziz Hussein

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

12. 2. Active Transport • Def. • It is movement of substances across the cell membrane against its electrochemical gradient. Biophysics , Abdelaziz Hussein

13. 3. Vesicular Transport • Def. • It is the process by which large sized substances are engulfed by the cell membrane to be either; • Pushed inside the cell (endocytosis) or • Pushed outside the cell (exocytosis) Biophysics , Abdelaziz Hussein

14. 3. Vesicular Transport

15. Diffusion

16. Diffusion

17. Diffusion It is movement of substances across the cell membrane down its electrochemical gradient due to the continuous random motion of its particles Biophysics , Abdelaziz Hussein

18. Diffusion Low concentration High concentration Biophysics , Abdelaziz Hussein

19. Diffusion It is divided into 3 subtypes: Simple diffusion. Facilitated diffusion. Osmosis (water only) Biophysics , Abdelaziz Hussein

20. Simple Diffusion Def It is movement of substances across the cell membrane down its electrochemical gradient by simple movement without the necessity of binding with carrier proteins Mechanisms: It occurs either through; Interstices of the lipid bilayer. Watery proteins channels. Biophysics , Abdelaziz Hussein

21. Simple Diffusion Lipid Interstitices Protein Channels

22. Simple Diffusion

23. Simple Diffusion • Characters: • It is characterized by; • Occurs down an electro-chemical gradient • Passive i.e. no external energy is required. Biophysics , Abdelaziz Hussein

24. Simple Diffusion Characters: c) It is not rate-limiting i.e. linear with concentration gradients. d) The diffusion process is not saturable. Biophysics , Abdelaziz Hussein

25. Diffusion through Lipid bilayers Biophysics , Abdelaziz Hussein

26. a. Diffusion of Lipid soluble substances • Mechanism: • Lipid soluble substance comes in contact with the membrane at one side and dissolved in the lipid matrix and transported to the other side • Rate of diffusion: • Its rate of diffusion is determined mainly by its lipid solubility • Example : • O2, nitrogen, CO2 diffusion Biophysics , Abdelaziz Hussein

28. b. Diffusion of water Water diffuses through lipid bilayer of the membrane at high rate like bullets due to; Small size. Very high kinetic energy Biophysics , Abdelaziz Hussein

29. C. Diffusion of water soluble substances • Urea diffusion • Is about 1000 times less than that of water • Its diameter is only 20% greater than that of H2O • Glucose • Is about 10,000 times less than that of water • Its diameter is only 3 times that of H2O) • Na and K ions diffusion: • Is about one million times less rapidly than does water • So, their transport must occur through protein channels Biophysics , Abdelaziz Hussein

31. Protein Channels

32. Simple Diffusion Through The Protein Channels

33. Diffusion through the Protein Channels Protein channels are watery pathways through the interstices of the protein molecules These channels are characterized by 1) Selective permeability 2) Gating of protein channels Biophysics , Abdelaziz Hussein

34. Selective Permeability of Protein Channels Most, but not all, protein channels are highly selective for the transport of one or more specific ions or molecules 1. Its diameter 2. Its shape Biophysics , Abdelaziz Hussein

35. Selective Permeability of Protein Channels • 3. Nature of the electrical charges of its inside surfaces • +ve charged channels for the passage of –ve charged particles. • -ve charged channels for the passage of +ve charged particles • Example: • Na channels for Na • K channels for K Biophysics , Abdelaziz Hussein

36. Gating of Protein Channels Many of the protein channels can be opened or closed by gates: Structure of gates The gates are extensions of the transport protein molecules close over the opening of the channel • Produce conformational change in the shape of protein molecule Biophysics , Abdelaziz Hussein

37. AS Biology, Cell membranes and Transport

38. Voltage gated Na Channels • Have 2 gates • Outer m gate • Inner h gate -Both m and h gate must be open for Na to flow through the Na channels Biophysics , Abdelaziz Hussein

39. Voltage gated Na Channels -When m gate is open → the channel is activated and Na ions can pass through it -When h gate is closed→ the channel is inactivated. Biophysics , Abdelaziz Hussein

40. K channels • Has one gate on the extracellular side (n gate). • n gate must be open for K+ to flow through the K+ channel Biophysics , Abdelaziz Hussein

41. THANKS