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Chapter 7: Warm-Up 1

Chapter 7: Warm-Up 1. Is the plasma membrane symmetrical? Why or why not? What types of substances cross the membrane the fastest? Why? Explain the concept of water potential. (Hint: Refer to Lab 1). Chapter 7: Warm-Up 2. What are glycoproteins and glycolipids and what is their function?

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Chapter 7: Warm-Up 1

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  1. Chapter 7: Warm-Up 1 • Is the plasma membrane symmetrical? Why or why not? • What types of substances cross the membrane the fastest? Why? • Explain the concept of water potential. (Hint: Refer to Lab 1)

  2. Chapter 7: Warm-Up 2 • What are glycoproteins and glycolipids and what is their function? • How do hydrophilic substances cross the cell membrane? • Why does water move through the bi-layer quickly?

  3. Chapter 7: Warm-Up 3 • Explain membrane potential and how it affects the cell. • In a U-tube, side A has 4 M glucose and 2 M NaCl. Side B has 2M glucose and 6 M NaCl. Initially, side A is ____ to side B and side B is ____ to side A. What happens if the membrane is permeable to both solutes? Only permeable to water and NaCl?

  4. Chapter 7: Warm-Up 4 • Side A in a U tube has 5M sucrose and 3 M glucose. Side B has 2 M sucrose and 1 M glucose. The membrane is permeable to glucose and water only. What happens to each side?

  5. Chapter 7: Warm-Up 5 • Side A in a U tube has 3 M sucrose and 1 M glucose. Side B has 1 M sucrose and 3 M glucose. The membrane is permeable to glucose and water only. What happens to each side?

  6. Chapter 7 Membrane Structure and Function

  7. What You Must Know: • Why membranes are selectively permeable. • The role of phospholipids, proteins, and carbohydrates in membranes. • How water will move if a cell is placed in an isotonic, hypertonic, or hypotonic solution. • How electrochemical gradients are formed.

  8. Cell Membrane • Plasma membrane is selectively permeable • Allows some substances to cross more easily than others • Fluid Mosaic Model • Fluid: membrane held together by weak interactions • Mosaic: phospholipids, proteins, carbs

  9. Early membrane model • (1935) Davson/Danielli – Sandwich model • phospholipid bilayer between 2 protein layers • Problems: varying chemical composition of membrane, hydrophobic protein parts

  10. The freeze-fracture method: revealed the structure of membrane’s interior

  11. Fluid Mosaic Model

  12. Phospholipids • Bilayer • Amphipathic = hydrophilic head, hydrophobic tail • Hydrophobic barrier: keeps hydrophilic molecules out

  13. Membrane fluidity • Low temps: phospholipids w/unsaturated tails (kinks prevent close packing) • Cholesterol resists changes by: • limit fluidity at high temps • hinder close packing at low temps • Adaptations: bacteria in hot springs (unusual lipids); winter wheat ( unsaturated phospholipids)

  14. Membrane Proteins Integral Proteins Peripheral Proteins • Embedded in membrane • Determined by freeze fracture • Transmembrane with hydrophilic heads/tails and hydrophobic middles • Extracellular or cytoplasmic sides of membrane • NOT embedded • Held in place by the cytoskeleton or ECM • Provides stronger framework

  15. Integral & Peripheral proteins

  16. Transmembrane protein structure Hydrophobic interior Hydrophilic ends

  17. Some functions of membrane proteins

  18. Carbohydrates • Function: cell-cell recognition; developing organisms • Glycolipids, glycoproteins • Eg. blood transfusions are type-specific

  19. Synthesis and sidedness of membranes

  20. Selective Permeability • Small molecules (polar or nonpolar) cross easily (hydrocarbons, hydrophobic molecules, CO2, O2) • Hydrophobic core prevents passage of ions, large polar molecules

  21. Passive Transport • NO ENERGY needed! • Diffusiondownconcentration gradient(high  low concentration) • Eg. hydrocarbons, CO2, O2, H2O

  22. Osmosis: diffusion of H2O

  23. External environments can be hypotonic, isotonic or hypertonic to internal environments of cell

  24. Facilitated Diffusion Transport proteins(channel or carrier proteins) help hydrophilic substance cross • (1) Provide hydrophilic channel or (2) loosely bind/carry molecule across • Eg. ions, polar molecules (H2O, glucose)

  25. Aquaporin: channel protein that allows passage of H2O

  26. Glucose Transport Protein(carrier protein)

  27. Active Transport • Requires ENERGY(ATP) • Proteins transport substances againstconcentration gradient(low  high conc.) • Eg. Na+/K+ pump, proton pump

  28. Electrogenic Pumps: generate voltage across membrane Na+/K+ Pump Proton Pump • Pump Na+ out, K+ into cell • Nerve transmission • Push protons (H+) across membrane • Eg. mitochondria (ATP production)

  29. Cotransport: membrane protein enables “downhill” diffusion of one solute to drive “uphill” transport of other Eg. sucrose-H+ cotransporter (sugar-loading in plants)

  30. Passive vs. Active Transport • Little or no Energy • High  low concentrations • DOWN the concentration gradient • eg. diffusion, osmosis, facilitated diffusion (w/transport protein) • Requires Energy (ATP) • Low  high concentrations • AGAINST the concentration gradient • eg. pumps, exo/endocytosis

  31. Bulk Transport • Transport of proteins, polysaccharides, large molecules Endocytosis: take in macromolecules, form new vesicles Exocytosis: vesicles fuse with cell membrane, expel contents

  32. Types of Endocytosis Phagocytosis: “cellular eating” - solids Pinocytosis: “cellular drinking” - fluids Receptor-Mediated Endocytosis: Ligands bind to specific receptors on cell surface

  33. BioFlix Animation Membrane Transport

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