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Cell membrane

Cell membrane. Phospholipids. Phosphate. “attracted to water”. Phosphate head hydrophilic Fatty acid tails hydrophobic Arranged as a bilayer. Fatty acid. “repelled by water”. Aaaah, one of those structure–function examples. Arranged as a Phospholipid bilayer.

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Cell membrane

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  1. Cell membrane

  2. Phospholipids Phosphate “attracted to water” • Phosphate head • hydrophilic • Fatty acid tails • hydrophobic • Arranged as a bilayer Fatty acid “repelled by water” Aaaah, one of thosestructure–function examples

  3. Arranged as a Phospholipid bilayer • Serves as a cellular barrier / border sugar H2O salt polar hydrophilic heads nonpolar hydrophobic tails impermeable to polar molecules polar hydrophilic heads lipids waste

  4. Cell membrane defines cell • Cell membrane separates living cell from aqueous environment • thin barrier = 8nm thick • Controls traffic in & out of the cell • allows some substances to cross more easily than others • hydrophobic (nonpolar) vs. hydrophilic (polar)

  5. Permeability to polar molecules? • Membrane becomes semi-permeable via protein channels • specific channels allow specific material across cell membrane inside cell H2O aa sugar salt outside cell NH3

  6. Cell membrane is more than lipids… • Transmembrane proteins embedded in phospholipid bilayer • create semi-permeabe channels lipid bilayer membrane protein channelsin lipid bilyer membrane

  7. Many Functions of Membrane Proteins “Channel” Outside Plasma membrane Inside Transporter Enzymeactivity Cell surfacereceptor “Antigen” Cell adhesion Cell surface identity marker Attachment to thecytoskeleton

  8. Membrane Proteins • Proteins determine membrane’s specific functions • cell membrane & organelle membranes each have unique collections of proteins • Classes of membrane proteins: • peripheral proteins • loosely bound to surface of membrane • ex: cell surface identity marker (antigens) • integral proteins • penetrate lipid bilayer, usually across whole membrane • transmembrane protein • ex: transport proteins • channels, permeases (pumps)

  9. Glycoprotein Glycolipid Transmembrane proteins Peripheral protein Filaments ofcytoskeleton Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Extracellular fluid Phospholipids Cholesterol Cytoplasm 1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model

  10. Membrane carbohydrates • Play a key role in cell-cell recognition • ability of a cell to distinguish one cell from another • antigens • important in organ & tissue development • basis for rejection of foreign cells by immune system

  11. Movement across the Cell Membrane

  12. Diffusion • 2nd Law of Thermodynamicsgoverns biological systems • universe tends towards disorder (entropy) • Diffusion • movement from HIGHLOW concentration

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

  14. 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 “The Bouncer”

  15. Getting through cell membrane • Passive Transport • Simple diffusion • diffusion of nonpolar, hydrophobic molecules • lipids • HIGH  LOW concentration gradient • Facilitated transport • diffusion of polar, hydrophilic molecules • through a protein channel • HIGH  LOW concentration gradient • Active transport • diffusion against concentration gradient • LOW  HIGH • uses a protein pump • requires ATP ATP

  16. Transport summary simplediffusion facilitateddiffusion ATP activetransport

  17. How about large molecules? • Moving large molecules into & out of cell • through vesicles & vacuoles • endocytosis • phagocytosis = “cellular eating” • pinocytosis = “cellular drinking” • exocytosis exocytosis

  18. Endocytosis fuse with lysosome for digestion phagocytosis non-specificprocess pinocytosis triggered bymolecular signal receptor-mediated endocytosis

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

  20. hypotonic hypertonic Concentration of water • Direction of osmosis is determined by comparing total solute concentrations • Hypertonic - more solute, less water • Hypotonic - less solute, more water • Isotonic - equal solute, equal water water net movement of water

  21. Managing water balance • Cell survival depends on balancing water uptake & loss freshwater balanced saltwater

  22. Do you understand 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

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