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7.3 Cell Boundaries

7.3 Cell Boundaries. Fluid compartments in our bodies are separated by membranes. Composition of body fluids. Greater number of osmotically active particles. Some organisms have a CELL WALL. Plants (cellulose) Algae (polysaccharide) Fungi (-chitin) Prokaryotes(peptidoglycan).

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7.3 Cell Boundaries

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  1. 7.3 Cell Boundaries

  2. Fluid compartments in our bodies are separated by membranes

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

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

  5. Why have a cell wall? • Mechanical support • Protection • Cell-cell communication • Maintenance of structure (turgor) • Prevent water loss

  6. Membranes

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

  8. 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?....

  9. Functions of the Cell membrane • Protective barrier • Cell-Cell signalling • Transport of nutrients, products and waste products • Localisation of function within organelles • Semi-permeable: controls entry and exit of substances • Self-sealing! • Flexible, mobile fluid mosaic Cell membrane function

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

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

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

  13. Porin monomer H+ Retinal chromophore b-pleated sheets NH2 Bacterial outer membrane Nonpolar (hydrophobic) a-helices in the cell membrane COOH Cytoplasm H+ Examples water channel in bacteria proton pump channel in photosynthetic bacteria function through conformational change (shape change)

  14. 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

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

  16. Movement across the Cell Membrane

  17. 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)

  18. 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

  19. Diffusion Movement is from HIGH to LOW concentration • “passive transport” • no energy needed movement of water diffusion osmosis

  20. Let’s watch some an animation of diffusion Diffusion animation 2

  21. inside cell outside cell Diffusion through phospholipid bilayer What molecules can get through directly? • fats & other lipids • What molecules can NOT get through directly? • polar molecules • H2O • ions • salts, ammonia • large molecules • starches, proteins lipid salt NH3 sugar aa H2O

  22. high low Facilitated Diffusion Diffusion through protein channels • channels move specific molecules across cell membrane • no energy needed facilitated = with help open channel = fast transport

  23. Channels for facilitated diffusion Membrane becomes semi-permeable with protein channels : specific channels allow specific material across cell membrane inside cell H2O aa sugar salt outside cell NH3

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

  25. OsmosisMovement of water across the cell membrane

  26. Osmosis is facilitated diffusion of water Facilitated diffusion of water from high concentration of water to low concentrationof wateracross a semi-permeable membrane

  27. hypotonic hypertonic Concentration of water 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 water net movement of water

  28. freshwater balanced saltwater

  29. Osmosis… .05 M .03 M Cell (compared to beaker)  hypertonic or hypotonic Beaker (compared to cell)  hypertonic or hypotonic Which way does the water flow?  in or out of cell

  30. Water passes through special water pores - Aquaporins

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

  32. Active Transport

  33. low high Active Transport Cells may need to move molecules against concentration gradient • shape change transports solute from one side of membrane to other • protein “pump” • “costs” energy = ATP conformationalchange ATP “The Doorman”

  34. Transport summary simplediffusion facilitateddiffusion ATP activetransport

  35. Endocytosis • A simple one... • McGRaw Hill phagocytosis

  36. Exocytosis • Protein produced by the ribosomes enter the lumen of the ER • Protein exits the ER and enters the cis or trans side of the Golgi aparatus • Protein is modified through Golgi, and vesiculated • Vesicle moves to and fuses with the plasma membrane • Exocytosis

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