2. Movement in and out of the cell membrane

3. Fluid compartments in our bodies are separated by membranes

4. Composition of body fluids Greater number of osmotically active particles

5. Some organisms have a CELL WALL Plants (cellulose) Algae (polysaccharide) Fungi (chitin) Prokaryotes(peptidoglycan)

6. Why have a cell wall? 1.Mechanical support 2.Protection 3.Cell-cell communication 4.Maintenance of structure (turgor) 5.Prevent water loss

7. Membranes 2007-2008

8. Where are membranes located? Plasma membrane (double membrane) Membrane-bound organelles (single or double) Secret Universe Introduction to cell membrane Introduction to cell membrane

9. Why do we need plasma membranes made Our cells inhabit an aqueous environment …but they must let ‘stuff’ (nutrients, ions, molecules,waste products) in and out …..and they need to communicate with each other… How is this achieved?....

10. Functions of the Cell membrane 1.Protective barrier 2.Cell-Cell signalling 3.Transport of nutrients, products and waste products 4.Localisation of function within organelles 5.Semi-permeable: controls entry and exit of substances 6.Self-sealing! 7.Flexible, mobile fluid mosaic Cell membrane function

11. Let’s meet the components of the cell membrane Phospholipid bilayer Cholesterol Carbohydrates (glycoproteins) Proteins

12. Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads

13. Membrane Proteins Proteins determine a membrane ’ s specific functions Cell membrane & organelle membranes each have unique collections of proteins Channels, pumps, receptors

14. NH 2 H+H+ COOH Cytoplasm Retinal chromophore Nonpolar (hydrophobic)  -helices in the cell membrane H+H+ Porin monomer  -pleated sheets Bacterial outer membrane proton pump channel in photosynthetic bacteria water channel in bacteria function through conformational change (shape change) Examples

15. Membrane glycoproteins (carbohydrates) ‘Chemical identification cards’ Play a key role in cell-cell recognition ability of a cell to distinguish one cell from another – Antigens basis for rejection of foreign cells by immune system

16. Let’s Review… Let's build a membrane from scratch… And now…let’s make a membrane!

17. Movement across the Cell Membrane

18. How do things get into and out of our cells? PASSIVE MECHANISMS These don’t require energy Simple diffusion Facilitated diffusion Osmosis ACTIVE MECHANISMS These require energy (usually ATP) to transport substances (often against their concentration gradient) Endocytosis/ exocytosis Protein pumps (cotransport)

19. Active Mechanisms: Endocytosis and Exocytosis A simple one... Animation Animation 2 Endocytosis/ exocytosis are import/export of materials by infolding/outfolding of the cell membrane

20. How do things get into and out of our cells? PASSIVE MECHANISMS These don’t require energy Simple diffusion Facilitated diffusion Osmosis ACTIVE MECHANISMS These require energy (usually ATP) to transport substances (often against their concentration gradient) Endocytosis/ exocytosis Protein pumps (cotransport)

21. Simple diffusion…in the real world Gas exchange in the lungs Gas exchange in plants

22. Simple Diffusion 2nd Law of Thermodynamics governs biological systems: the universe tends towards disorder (entropy) Diffusion : movement of small, soluble particles from high  low concentration

23. Diffusion Movement is from HIGH to LOW concentration “ passive transport ” no energy needed diffusionosmosis movement of water

24. Factors affecting diffusion 1.Temperature 2.Surface area for diffusion 3.Distance for diffusion 4.(size of particle) 5.(charged or uncharged)

25. Diffusion in the real world Diffusion animation 2 Gas exchange at the alveoli — oxygen from air to blood, carbon dioxide from blood to air. Gas exchange for photosynthesis — carbon dioxide from air to leaf, oxygen from leaf to air. Gas exchange for respiration — oxygen from blood to tissue cells, carbon dioxide in opposite direction. Transfer of neurotransmitter substance at a nerve synapse. Osmosis — diffusion of water through a semipermeable membrane.

26. Facilitated Diffusion Facilitated diffusion is diffusion of specific molecules through protein channels in the cell membrane – no energy is required open channel = fast transport facilitated = with help high low

27. Channels for facilitated diffusion Membrane becomes semi-permeable with protein channels : specific channels allow specific material across cell membrane inside cell outside cell sugaraa H2OH2O salt NH 3

28. Which substances are transported by facilitated diffusion? Glucose Urea Amino acids Animation

29. Factors affecting the rate of facilitated diffusion are the same as for simple diffusion 1.Temperature 2.Surface area for diffusion 3.Distance for diffusion

30. Osmosis A special case: facilitated diffusion of water molecules across a semi- permeable membrane

31. Osmosis is facilitated diffusion of water Facilitated diffusion of water from high concentration of water to low concentration of water across a semi-permeable membrane

32. Examples of Osmosis in Biology Absorption of water by plant roots. Re-absorption of water in the kidney. Re-absorption of tissue fluid into blood capillaries. Absorption of water in the GI tract

33. Water passes through special water pores - Aquaporins

34. Aquaporins Structure, function and dynamics of aquaporins Structure, function and dynamics of aquaporins Peter Agre John Hopkins Roderick MacKinnon Rockefeller

35. Water moves across a membrane from the hypotonic solution to the hypertonic solution Animation of osmosis 1 Animation of osmosis 2: why water balance matters Animation of osmosis 2: why water balance matters

36. Comparing ‘water concentration’ of different solutions Direction of osmosis is determined by comparing total solute concentrations on either side of the membrane: Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water hypotonichypertonic water net movement of water

37. freshwaterbalancedsaltwater

38. Water potential? It can be confusing to talk about the concentration of water molecules, since ‘concentration’ is usually reserved for a solute (e.g. glucose, Instead we use the term water potential High water potential = lots of water (high water concentration/ low solute concentration LOW water potential = little water (low water concentration/high solute concentration) Water moves from a region of high water potential to a region of low water potential

39. Low water potential (relatively few water molecules compared to solute molecules) High water potential (relatively many water molecules compared to solute molecules)

41. How do things get into and out of our cells? PASSIVE MECHANISMS These don’t require energy Simple diffusion Facilitated diffusion Osmosis ACTIVE MECHANISMS These require energy (usually ATP) to transport substances (often against their concentration gradient) Protein pumps Endocytosis (cotransport)

42. Active transport 1: Protein pumps Active transport uses energy (ATP) to transport substances AGAINST a concentration gradient into/out of the cell The energy is used to change the shape of the ‘protein pump’ and thus import/export specific molecule Animation protein pumps in plants ATP low high

43. Active transport in the real world Re-absorption of glucose, amino acids and salts in the kidney. Sodium/potassium pump in cell membranes (especially nerve cells) Uptake of nutrients (e.g. nitrate ions)in plant root hair cells

44. Transport summary simple diffusion facilitated diffusion active transport ATP