Membranes pt. 2

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Membranes pt. 2
2013-09-20 21:22:52
Cell Bio

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  1. How would each phospholipid be oriented in a membrane?
    - sphingolipids
    - glycolipids
    - steroids
    - cardiolipin
    • - sphingolipids: heads out (hydrophilic); tail in
    • - glycolipids: tail in; sugar outside
    • - steroids: nestles up against the bottom of the hydrophobic tails
    • - cardiolipin: has to fold (U-shaped) (R1 and R2 are hydrophobic)
  2. What are the advantages (consequences, importance) to a cell of the presence of lipid in the membrane?
    • selective permeability (allows access to some; polar molecular ions need help)
    • allows buildup of concentration of cells 
    • structure (if hydrophilic, they'd dissolve)
    • energy saving
  3. Explain the energy saving advantage of lipids?
    because of their chemical nature, if you put them in a particular environmnt, they will spontaneously form a bilayer with no energy needed (preferred arrangement)
  4. Working outside of cells and not in them: __
    Working inside of cells and with them: __
    • in vitro
    • in vivo
  5. True or False. Explain
    Membranes in cells never have a free end.
    • True
    • because it will cause exposure of hydrophilic regions
    • - allows for cell division, splitting, etc.
  6. Arrangements of Membrane: first model?
    Davson-Danielli Model (1935)
  7. What was the Davson-Danielli Model
    • sugar proteins on outside (globular)
    • lipids inside (sandwich model)
  8. What was the Davson-Danielli revision made?
    there may be some hydrophilic pores
  9. Second model
    Robertson Unit Membrane Model (1960)
  10. What is the difference of the Robertson Unit Membrane Model?
    shape of protein; he stated theywere extended, not globular
  11. Why did the RUM model state what it stated?
    • said this because he looked at cells with better EM
    • also,  new fixative was introduced
  12. Explain the fixatives Robertson used?
    • the old was osmium tetroxide: you would see it as a solid black line
    • the new one: potassium permanganate allows you to see two solid black lines with a line in between (you can even measure the space and black lines)
  13. Evidence supporting the RUM theory: 
    a densely packed lipid bilayer can account for high percentages of lipid found in membranes
  14. Evidence supporting the RUM theory: 
    • lipids are poor electron conductors
    • - if you have alot= you have high resistance
  15. Evidence supporting the RUM theory: 
    • increased permeability to non-polar molecules 
    • - allows it to get through easily
    • - polar molecules do not
  16. Evidence supporting the RUM theory:  
    phospholipid will spontaneously form bilayers in water
  17. Evidence supporting the RUM theory: 
    accounts for electron micrograph he was seeing
  18. The first four points of evidence deal with __.
    What don't the five points talk about?
    • lipid
    • proteins
  19. Third model
    Singer and Nicholson's Fluid Mosaic Model
  20. The fluid mosaic model has been around for about __.
    forty years
  21. Similarities of fluid mosaic, DD, and RUM.
    • phospholipid bilayer
    • there are proteins
  22. Differences between fluid mosaic, DD, and RUM.
    arrangement of proteins
  23. Two basic categories of proteins
    • peripheral 
    • integral
  24. The proteins that were in the same position as the DD and RUM models were __. 
    How prominent are they?
    • peripheral (extrinsic) proteins
    • in the minority 
  25. The majority of proteins are __. They are embedded in the __ and are __ present. 
    • integral (intrinsic)
    • membranes
    • 70-80% (majority)
  26. is the lipid composition the same in every membrane?
    no, it varies
  27. Is the chemical composition the same of various cell membranes?
    no, it varies
  28. What does phosphatidyl indicate?
    that the lipid is a phospholipd
  29. __ comprise another category of lipids found in membranes. Here again, there is a great variety of complex compounds. The structure common to all of the compounds is a __ on which two other __ are substituted. 
    • sphingolipids
    • sphingosine residue
    • residues
  30. R1 on a sphingolipid may be __ while R2 can __. 
    • a variety of fatty acids
    • vary widely
  31. In a sphingomyelin, there are __ and __ regions. There are two __ and a __. The latter is called is __ because it carries both a negatively charged group.
    • polar 
    • nonpolar
    • hydrophobic tails
    • strongly hydrophilic head
    • zwitterion
  32. What is the hydrophilic portion of a steroid? 
    hydrophobic portion?
    • hydrophilic: the -OH group
    • hydrophobic: the rest of hte structure
  33. What is the hydrophilic portion of a glycolipd? 
    hydrophobic portion?
    • hydrophilic: the sugar residue (such as galactose)
    • hydrophobic: the rest of hte structure
  34. Like phospholipids, glycolipids are composed of a __ and a __. 
    • hydrophic region containing two long hydrocarbon tails
    • polar region (one or more sugar residues and no phosphate)
  35. A cardiolipin has to have what occur?
    it has to fold inward so that its hydrophobic R groups are away from aqueous solution
  36. Who came up with the term unit membrane?
  37. WHat were the masurements Robertson made of his model?
    • 20 angstroms protein each side
    • 35 angstrons phospholipid
    • = 75 angstroms
  38. What are the requirements for dissociation from the membrane of :
    peripheral proteins
    mild treatment sufficient; high ionic strength, metal ion chelating agents will cause them to easily come off
  39. What are chelating agents?
    molecuels that hold onto something tightly (hold peripheral proteins)
  40. Examples of peripheral proteins
    • cytochrome C
    • protein kinases
  41. What are the requirements for dissociation from the membrane of :
    integral proteins
    • hydrophobic bond-breaking agents required: detergents, organic solvents, chaotropic agents
    • really have to beat the membrane up and take it apart 
  42. Association with lipids when solubilized: 
    peripheral proteins
    usually soluble free of lipids; if you can get proteins out of the membrane, the lipids don't usually come with these proteins
  43. Association with lipids when solubilized: 
    usually associated with lipids when solubilized
  44. Solubility after dissociation from membrane: 
    peripheral proteins
    soluble and moleculary dispersed in neutral aqueous buffers
  45. Solubility after dissociation from membrane: 
    integral proteins
    usually insoluble or aggregated in neutral aqueous buffers
  46. How many classes of integral proteins?
    • four
    • two are partially embedded
    • transmembrane
    • complex of proteins
  47. How are membrane proteins classified?
    according to their mode of attachment to the membrane
  48. Integral membrane proteins contain one or more __ that are embedded within the __.
    • hydrophobic regions
    • lipid bilayer
  49. A few integral proteins appear to be embedded in the membrane on only one side of the bilayer (__)
    integral monotopic proteins
  50. However, most integral proteins are __ that span the lipid bilayer either once (__) or multiple times (__).
    • singlepass proteins
    • multipass proteins
  51. __ can consist of either a __ or several __ (__).
    • multipass proteins
    • single polypeptide
    • several associated polypeptides (multisubunit proteins)
  52. Peripheral membrane proteins are __ but are attached to the membrane by __ and __ that link them to adjacent membrane proteins or to __.
    • too hydrophilic to penetrate into the membrane 
    • electrostatic
    • hydrogen bonds
    • phospholipid head groups
  53. __ are hydrophilic and do not penetrate into the membrane; they are __ to lipid molecules that are embedded in the lipid bilayer.
    • lipid anchored proteins
    • covaletly
  54. Proteins on the inner surface fo the membrane are usually anchored by either a __ or a __ group. On the outer membrane surace, the most common lipid anchor is __,
    • fatty acid
    • prenyl group
    • glycosylphosphatidylinositol (GPI)

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