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Chapter 7

Chapter 7. Membrane Structure/ Function and Cell Transport Ms. Gaynor AP Biology. Overview of Cell Membrane. The plasma (cell) membrane the boundary that separates living cell from its nonliving surroundings Also called the phospholipid bilayer.

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Chapter 7

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  1. Chapter 7 Membrane Structure/ Function and Cell Transport Ms. Gaynor AP Biology

  2. Overview of CellMembrane • The plasma (cell) membrane • the boundary that separates living cell from its nonliving surroundings • Also called the phospholipid bilayer

  3. The plasma membrane exhibits selective permeability. It is semi-permeable • It allows some substances to cross it more easily than others Wow… it’s so detailed!

  4. Cellular membranes are made of 2 types of lipids and proteins • LIPID #1: Phospholipids • most abundant lipid in membrane • They are amphipathic • have both hydrophobic and hydrophilic regions

  5. WATER Hydrophilic head Hydrophobic tail WATER Figure 7.2 Phospholipid Bilayer • Phosphate Groups in “head” (- charge) • 2 Fatty Acids in “tail” (hydrocarbon) NO WATER

  6. Hydrophobic region of protein Phospholipid bilayer Hydrophobic region of protein • In 1972, scientists • Proposed that membrane proteins are mixed in and individually inserted into the phospholipid bilayer Hey, that looks like a sandwich!

  7. Fluid Mosaic Model of the cell membrane Polar heads love water & dissolve. Membrane movement animation Non-polar tails “hide” from water. Carbohydrate cell markers Proteins

  8. Lateral movement (~107 times per second) Flip-flop (~ once per month) (a) Movement of phospholipids Figure 7.5 A The Fluidity of Membranes • Phospholipids in the plasma membrane • Can move within the bilayer • Proteins are larger & drift (move) less

  9. Another view…

  10. Fluid Viscous Unsaturated hydrocarbon tails with kinks Saturated hydro- Carbon tails (b) Membrane fluidity Figure 7.5 B • Temperature decreases  so does fluidity • Hydrocarbon tails in phospholipids • Affects fluidity of the plasma membrane • Need to have some unsaturated fatty acid tails Fluidity is enhanced

  11. Cholesterol (c) Cholesterol within the animal cell membrane LIPID #2:steroid “cholesterol” has different effects on membrane fluidity at different temperatures (only in animal cells) -lower temps  lowers lipid movement  lowers fluidity- cholesterol in membrane  hinders (stops) solidification **acts as a temp “buffer”

  12. Glycoprotein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Microfilaments of cytoskeleton Peripheral protein Cholesterol Integral protein CYTOPLASMIC SIDE OF MEMBRANE Membrane Proteins and Their Functions • A membrane • Includes different proteins embedded in the fluid lipid bilayer Fibers of extracellular matrix (ECM) 2 major types of membrane proteins

  13. CYTOPLASMIC SIDE a Helix Figure 7.8 1. Integral proteins Wait…what’s that word for a polar & nonpolar molecule? • Penetrate the hydrophobic core of the lipid bilayer • Are often transmembrane proteins, completely spanning the membrane Span of 1+ stretches of Nonpolar amino acids EXTRACELLULAR SIDE

  14. 2. Peripheral proteins • Are appendages loosely bound to the surface of the membrane

  15. Transport. (a) Enzymatic activity. (b) Enzymes (c) Signal Signal transduction. Receptor An overview of six major functions of membrane proteins

  16. Cell-cell recognition. (d) Glyco- protein Intercellular joining (e) (f) Attachment to cytoskeleton & extracellular matrix (ECM) ECM

  17. REVIEW….

  18. Why have Carbohydrates on Cell Membrane proteins? • Cell-cell recognition • Is a cell’s ability to distinguish one type of neighboring cell from another • It’s their “ID” tag

  19. Membrane carbohydrates • Usually short, branched carbohydrates • Interact (bind) with the surface molecules of other cells • Function as cell “markers” • Ex: Blood types (A, B, AB, and O)

  20. 2 different types membrane carbohydrates • Glycolipids • Carbohydrates covalently attached to lipids • Glycoproteins • Carbohydrates covalently attached to proteins (most abundant)

  21. Review… Animations of membrane structure

  22. Chapter 7 Cell Transport Ms. Gaynor AP Biology

  23. Remember…Cell Membranes are FLUID MOSAIC MODELSLET’S REVIEW THE CELL MEMBRANE • http://www.hippocampus.org/Biology • Click on “Membranes and Transport” • Listen to animation #1 and #2 (8 minutes long)…get ready!!!

  24. Membrane structure LEADS TO selective permeability • A cell must exchange materials with its surroundings • a process controlled by the selectively permeableplasma membrane

  25. Cell Transport • Means moving things INTO and OUTof the cell • Cells need to take in • Food, gases, water • Get rid of waste products (excretion) • Give out such useful substances as hormones and enzymes (secretion).

  26. Permeability and Cell Transport • Hydrophobic (non polar) molecules • Are lipid soluble (can dissolve) • can pass through membrane easily • Ex: Hydrocarbons, CO2, O2 • Hydrophilic (Polar) molecules • Are NOT lipid soluble (can’t dissolve) • Lipid INsoluble • Do not cross membrane easily • Ex: Na+, Cl- , Glucose/ other sugars • NOTE: CHARGED molecules need “help” to cross membrane

  27. Weee! high low This is going to be hard! high low Types of Cellular Transport • Passive Transport cell do NOT use energy • Diffusion • Facilitated Diffusion • Osmosis • Active Transport cell DOESuse energy • Protein Pumps • Endocytosis • Exocytosis

  28. Types of Passive Transport Diffusion= tendency for a population of molecules (of ANY substance) to spread out evenly into available space • A “net” movement • Ex: Perfume, a fart , tea, food coloring in water • http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion2.gif • http://www.biosci.ohiou.edu/introbioslab/Bios170/diffusion/Diffusion.html • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

  29. DIFFUSION • In absence of other forces… • Molecules move (diffuse) from area of HIGH [ ] to an area of lower [ ] • A.k.a. Molecules move DOWN its OWNconcentration gradient • the difference in [ ] of a substance from one area to another • No chemical work (ATP energy) is used diffusion is spontaneous!

  30. (b) Equilibrium Net diffusion Net diffusion Net diffusion Equilibrium Net diffusion Figure 7.11 B Substances diffuse down their OWN concentration gradient

  31. Factors Affecting Diffusion 1. Temperature • Higher temperature  more kinetic energy  molecules move faster (Example: Tea) 2. Pressure • Higher pressure  molecules move faster

  32. Effects of Osmosis on Water Balance Osmosis • The movement of water(water diffusion)across a semipermeable membrane • Involves the movement of FREE water molecules down a water [ ] gradient • High solute low “free” water [ ] or…. • Low solute  high free water [ ]

  33. Osmosis is affected by the concentration gradient of dissolved substances (solutes) Osmosis animation

  34. 3 Different Types of SolutionsRecall: SOLUTION = a uniform mixture of 2 or more substances** compare solutions OUTSIDE cell to inside cell 1. If a solution is isotonic • [solutes] is the same outside as inside the cell • “iso-” means “same” • There will be NO net movement of water

  35. ISOTONIC SOLUTION Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)

  36. 2. If a solution is hypertonic • [solutes] is greater outside than inside the cell The cell will lose water and shrivel or wilt • “hyper” means more • (high [solute]) • Ex: when salinity increases in lake, fish can die!

  37. HYPERTONIC SOLUTION Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)!

  38. 3. If a solution is hypotonic • [solutes] is less outside than it is inside the cell The cell will gain water and swell (and maybe lyse or burst) • “hypo” means “less” • (low [solute]) • Think: Hypo- sounds like hippo…hippos are big & round; cells in hypotonic solutions get big & round • Also, think “hypo” is “low” meaning “low” solutes SURROUNDING cell “Hypo” is LOW!!!

  39. HYP0TONIC SOLUTION Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)!

  40. Osmosis Animations for isotonic, hypertonic, and hypotonic solutions http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

  41. Water Balance of Cells with Walls • Cell walls • Help maintain water balance • Cell walls are in: • Plants • Prokaryotes • Fungi • Some protists

  42. If a plant cell is turgid • It is in a hypotonic environment • It is very firm • A healthy state in most plants • If a plant cell is flaccid • It is in an isotonic or hypertonic environment • Cells are limp • Plasmolysis= when plasma membrane pulls away from cell wall in hypertonic solutions ; causes cell with walls to wilt & can be lethal.

  43. (b) H2O H2O Plant cell. Plant cells are turgid (firm) and generally healthiest in a hypotonic environ- ment, where the uptake of water is eventually balanced by the elastic wall pushing back on the cell. H2O H2O Turgid (normal) Flaccid Plasmolyzed Figure 7.13 Water balance in cells with walls

  44. How Organisms Deal with Osmotic Pressure • Bacteria and plants have cell walls that prevent them from over-expanding. • In plants the pressure exerted on the cell wall is called tugor pressure. • A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from bursting. • Salt water fish pump salt out of their specialized gills so they do not dehydrate. • Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.

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