1 / 19

Ch 7 Membrane Structure and Function

Ch 7 Membrane Structure and Function. Cellular membrane -overall functions. - Boundary between intracellular compartments, living cells, and abiotic environment Selectively permeable Some molecules cross membranes more readily than others. Membrane Structure.

kolya
Download Presentation

Ch 7 Membrane Structure and Function

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Ch 7 Membrane Structure and Function

  2. Cellular membrane -overall functions - Boundary between intracellular compartments, living cells, and abiotic environment • Selectively permeable • Some molecules cross membranes more readily than others

  3. Membrane Structure Predominant constituent: phospholipids • Amphipathic molecules: hydrophobic AND hydrophilic Dispersed protein components Membrane organization and properties described by: Fluid Mosaic Model Singer and Nicolson 1972

  4. Organization of membrane phospholipids LE 7-2 WATER Hydrophilic head Hydrophobic tail WATER

  5. Mosaic: something made of small pieces

  6. Mosaic: Proteins dispersed among phospholipids in membrane: LE 7-3 Hydrophilic region of protein Phospholipid bilayer Hydrophobic region of protein

  7. Freeze-fracture studies of the plasma membrane • Frozen membrane split along the middle of the phospholipid bilayer using a knife • Imaged by EM Supports mosaic part of model

  8. Extracellular layer LE 7-4 Proteins Knife Plasma membrane Cytoplasmic layer Extracellular layer Cytoplasmic layer

  9. The Fluidity of Membranes • Phospholipids move laterally within the bilayer • Some membrane proteins also drift laterally • Rarely does a phospholipid flip-flop transversely across the membrane

  10. LE 7-5a Lateral movement (~107 times per second) Flip-flop (~ once per month) Movement of phospholipids

  11. Effects of Temperature on membranes • Cool temp: membranes switch from fluid to more solid state • Solidification depends on type of lipid • What property of lipids would favor liquid versus solid state?

  12. Degree of saturation of fatty acid tails LE 7-5b Viscous Fluid Saturated hydro- carbon tails Unsaturated hydrocarbon tails with kinks Membrane fluidity

  13. Steroid cholesterol also component of membranes • Tends to moderate effects of temp. on membrane state • At warm temperatures (such as 37°C), restrains movement of phospholipids • At cool temperatures, maintains fluidity by preventing tight packing

  14. LE 7-5c Cholesterol Cholesterol within the animal cell membrane

  15. Movement of membrane proteins Can drift within the bilayer • Proteins much larger than lipids--> move more slowly • Cell fusion studies support fluidity of membrane proteins

  16. LE 7-6 Membrane proteins Mouse cell Mixed proteins after 1 hour Human cell Hybrid cell

  17. Membrane Proteins and Their Functions • Proteins determine most of the membrane’s specific functions • Peripheral membrane proteins • not embedded • attached to extracellular or cytoplasmic surface • Integral membrane proteins • penetrate the hydrophobic core of bilayer • often span the membrane

  18. Fibers of extracellular matrix (ECM) LE 7-7 Glycoprotein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Cholesterol Peripheral proteins Microfilaments of cytoskeleton Integral protein CYTOPLASMIC SIDE OF MEMBRANE

More Related