Understanding Cell Membranes & Transport Processes in Human Physiology

1. Human Physiology: Unit-1 Cell Membranes transport across cell and membrane BY DR BOOMINATHAN Ph.D. M.Sc.,(Med. Bio, JIPMER), M.Sc.,(FGSWI, Israel), Ph.D (NUS, SINGAPORE), PDF (USA) PONDICHERRY UNIVERSITY IV Lecture 9/August/2012 Source: Collected from various sources on the internet and modified by Dr Boominathan Ph.D.

2. Cell Membranes& Movement Across Them

3. Cell (plasma) membrane • Cells need an inside & an outside… • separate cell from its environment • cell membrane is the boundary IN food - sugars - proteins - Lipids -salts -O2 -H2O OUT waste - ammonia - salts - CO2 - H2O products - proteins cell needs materials in & products or waste out

4. Building a membrane • How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? LIPIDS Remember: oil & water don’t mix!! What substance do you know that doesn’t mix with water?

5. inside cell outside cell Lipids of cell membrane • Membrane is made of special kind of lipid • phospholipids • Membrane is a double layer • phospholipid bilayer “attracted to water” phosphate lipid “repelled by water”

6. Semi-permeable membrane • Cell membrane controls what gets in or out • Need to allow some materials — but not all — to pass through the membrane • semi-permeable • only some material can get in or out So what needs to get across the membrane? lipids aa O2 H2O salt sugar waste

7. inside cell outside cell Crossing the cell membrane • What molecules can get through the cell membrane directly? • fats and oils can pass directly through lipid salt waste but… what about other stuff? sugar aa H2O

8. Cell membrane channels • Need to make “doors” through membrane • protein channels allow substances in & out • specific channels allow specific material in & out • H2O channel, salt channel, sugar channel, etc. inside cell H2O aa sugar salt outside cell waste

9. How do you build a semi-permeable cell membrane? • Channels are made of proteins • proteins both “like” water & “like” lipids bi-lipid membrane protein channelsin bi-lipid membrane

10. Protein channels • Proteins act as doors in the membrane • channels to move specific molecules through cell membrane HIGH LOW

11. Movement through the channel • Why do molecules move through membrane if you give them a channel? HIGH ? LOW ?

12. Molecules move from high to low • Diffusion • move from HIGH to LOW concentration

13. Diffusion • Move from HIGH to LOW concentration • passive transport • no energy needed diffusion of water diffusion osmosis

14. Diffusion (without energy-simple) • Move from HIGH to LOW Which way will Lipid substances move? Lipid Lipid inside cell LOW HIGH Lipid Lipid Lipid outside cell Lipid Lipid Lipid

15. Facilitated Diffusion • Move from HIGH to LOWthrough a channel sugar sugar sugar sugar inside cell sugar sugar LOW Which way will sugar move? HIGH outside cell sugar sugar sugar sugar sugar sugar sugar

16. Diffusion • Move from HIGH to LOW concentration • directly through membrane • simple diffusion • no energy needed • help through a protein channel • facilitated diffusion (with help) • no energy needed HIGH LOW

17. inside cell inside cell outside cell outside cell Simple vs. facilitated diffusion simple diffusion facilitated diffusion lipid H2O protein channel H2O

18. Active transport • Cells may need molecules to move against concentration “hill” • need to pump “uphill” • from LOW to HIGHusing energy • protein pump • requires energy • ATP ATP

20. Transport summary simplediffusion facilitateddiffusion ATP activetransport

21. OsmosisMovement of Water Across Cell Membrane

22. Osmosis • Water is very important, so we talk about water separately • Osmosis • diffusion of water from HIGH concentration of water to LOW concentration of water • across a semi-permeable membrane

23. Keeping water balance • Cell survival depends on balancing water uptake & water loss freshwater balanced saltwater

24. 1 Keeping right amount of water in cell • Freshwater • a cell in fresh water • high concentration of water around cell • cell gains water • example: Paramecium • problem: cells gain water,swell & can burst • water continually enters Paramecium cell • solution: contractile vacuole • transports water out of cell Burst freshwater No problem,here

25. 2 Keeping right amount of water in cell I’m shrinking,I’m shrinking! • Saltwater • a cell in salt water • low concentration of water around cell • cell loses water • example: shellfish • problem: cell loses water • in plants: plasmolysis • in animals: shrinking cell • solution: take up water saltwater I willsurvive!

26. 3 Keeping right amount of water in cell • Balanced conditions • no difference in concentration of water between cell & environment • cell in equilibrium • example:blood • problem: none • water flows across membrane equally, in both directions • volume of cell doesn’t change That’sbetter! balanced I couldbe better…

27. CELLS

28. Chemical compositions of extracellular and intracellular fluids Downloaded from: StudentConsult (on 15 August 2012 04:30 AM)

29. Na-K Channel: How it Works • A type of active transport. • 3 sodium ions move out of cell • 2 potassium ions move into cell. • ATP is needed as each of these ions are moving against their conc. gradient. • Mostly used in cardiac muscle and nervous tissue. Maintains Na+K gradient concentration. • Huge amount of ATP goes into this NaK channel.

30. Sodium –Potassium Channel Figure 3.11

31. Sodium-Potassium Channel A molecule of ATP is used with each “swap of Na/K ions

32. Endocytosis (phagocytosis-Cell Eating) • This is Vessicle transport during which the entire plasma membrane folds inward allowing large particles into the cell. • Ex; the cell is ingesting microbes , perhaps?

33. AS Biology, Cell membranes and Transport Cell Membrane - Function - Endocytosis The cell membrane can also engulf structures that are much too large to fit through the pores in the membrane proteins this process is known as endocytosis. In this process the membrane itself wraps around the particle and pinches off a vesicle inside the cell. In this animation an ameba engulfs a food particle.

35. Exocytosis • The opposite of ENDOcytosis. Large particles are leaving the cell. (digested microbes for example).

37. Receptor- Mediated Endocytosis Viruses are species –specific , and receptor specific, transmitted via receptor-mediated endocytosis.

38. AS Biology, Cell membranes and Transport Vesicle-mediated transport Vesicles and vacuoles that fuse with the cell membrane may be utilized to release or transport chemicals out of the cell or to allow them to enter a cell. Exocytosis is the term applied when transport is out of the cell.

39. Cell Membrane (Transport) Notes • Cell Membrane and Cell Wall: • ALLcells have a cell membrane made of proteins and lipids protein channel Layer 1 Cell Membrane Layer 2 lipid bilayer protein pump Cell Membrane Cell Wall • SOME cells have cell membranes andcell walls – ex: plants, fungi and bacteria

40. Plant cells have a cell wall made of cellulose – that cellulose is fiber in our diet • Bacteria and fungi also have cell walls, but they do not contain cellulose • Cell membranes and cell walls are porous allowing water, carbon dioxide, oxygen and nutrients to pass through easily

41. Function of the Cell Membrane: • Cell membrane separates the components of a cell from its environment—surrounds the cell • “Gatekeeper” of the cell—regulates the flow of materials into and out of cell—selectively permeable • Cell membrane helps cells maintain homeostasis—stable internal balance

42. Passive Transport • A process that does not require energy to move molecules from a HIGH to LOW concentration • Diffusion • Facilitated Diffusion • Osmosis

43. outside of cell inside of cell • Diffusion is the movement of small particles across a selectively permeablemembrane like thecell membrane until equilibrium is reached. • These particles move from an area of high concentrationto an area of low concentration.

44. Diffusion HIGH to LOW concentration

45. Osmosis is the diffusion of water through a selectively permeable membrane like the cell membrane • Water diffuses across a membrane from an area of high concentration to an area of low concentration. Semi-permeable membrane is permeable to water, but not to sugar

48. Glucose molecules outside of cell inside of cell • Facilitated Diffusion is the movement of larger molecules like glucose through the cell membrane – larger molecules must be “helped” • Proteins in the cell membrane form channels for large molecules to pass through • Proteins that form channels (pores) are called protein channels

50. Hypertonic Solutions: contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel. Hypotonic Solutions: contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffusesinto the cell, causing the cell to swell and possibly explode. Isotonic Solutions: contain the same concentration of solute as another solution (e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water diffusesinto and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.