Membrane Structure

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Membrane Structure
2012-10-20 15:14:36

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  1. __: allows some substances to cross more easily than others


    __ model: __.
    selective permeability

    • lipids and proteins, adn some carbs
    • -- phospholipids
    • ----- Amphipathic moleculesl (contain both hydrophilic and hydrophobic regions)
    •   --------- proteins are too

    Fluid mosaic model: membrane is a fluid structure with a mosaic of various proteins embedded in or attached to double layer of phospholipids
  2. Explain the theories and protegression of discovery
    • 1) composed of lipids adn proteins
    • 2) phospholipid bilayer
    • 3) Davson- Danielli model
    • 4) Singer and Nicolson's fluid mosaic model
  3. Explain the Davson_Danielli model.
    sandwich model: a phospholipid bilayer between two layers of proteins with both sides being hydrophilic

    • Problems:
    • membranes with different functions differ in chemical composition and structure
    • membrane proteins are amphipathic and not soluble in water)
  4. What did Singer and Nicolson suggest?
    hydrophilic regions protruding and hydrophobic parts away
  5. Methods for preparing cells for EM
    •                                                               i.     
    • Freeze- fracture

    • 1.     
    • Splits membrane along middle of
    • bilayer

    • a.     
    • Interior: cobblestoned with protein
    • particles interspersed in smooth matrix
  6. Models are __. Acceptance or rejection changes with observations and experimental results--> revised, such as fluid mosaic model.
  7. Fluidity of Membranes
    i. Membrane held together by__, weaker than ___
    ii. Most lipids and some proteins shift __; rarely do they __
    iii. Membrane proteins move __rapidly and move in __ manner (some); many others are __by attachment to __
    •  hydrophobic interactions
    • covalent bonds
    • laterally (rapid movement)
    • flip-flop
    • less
    • highly directed
    • immobile
    • ECM or cytoskeleton
  8. Temperature and Fluidity
    - What happens with temp decrease?
    - What does temperature of freezing depend on
    ex:  Rich in phospholipids with unsaturated hydrocarbon
    • remains fluid until packed arrangement creates solidification
    • types of lipids
    • remains fluid at lower temperature because kinks
    • prevent close packing
  9. Cholesterol and Membrane Fluidity
    Cholesterol wedged between phospholipids in animal membranes to act as __. Explain
    • fluidity buffer
    • 1. High temperatures: cholesterol makes less fluid by restraining phospholipid movement 
    • 2. Low temperatures: hidners close packing of phospholipids, thus lowering temperature required for membrane to solidify
  10. Membranes must be __ to work properly. 
    1. When solidifies, its __changes, and __may become inactive if activity requires movement

    a. Still, too much fluidity cannot support protein function either
    • fluid
    • permeability
    • enzymatic proteins
  11. i. Variations in cell membrane lipid compositions are __to maintain appropriate membrane fluidity in specific conditions

    ii. Ability to change __ of cell membranes in response to changing temperatures evolved in organisms that live __

    ex: Plants that tolerate extreme cold: ??

    iii. __favors mix of membrane lipids to ensure appropriate fluidity
    • evolutionary
    • lipid composition
    • where temperatures vary
    • unsaturated phospholipids increase in autumn to prevent solidification
    • Natural selection
  12. Membrane PRoteins
    1) collage
    --- more than fifty found so far
    --- Although __ dominate, __determine functions
    2) Two types
    • phospholipids
    • proteins
    • integral/ peripheral
  13. Integral:
    a) location
    b) __regions of integral protein consist of one or more stretches of __, usually coiled into __. 
    c) __parts exposed to aqueous solutions
    d) Also contain__ that allows passage of hydrophilic substances
    • a. Penetrate hydrophobic interior of the lipid bilayer
    •    i. Majority: transmembrane proteins: span the membrane
    •   ii. Others extend partway into hydrophobic interior
    • Hydrophobic
    • nonpolar amino acids
    • α-helices
    • Hydrophilic
    •  hydrophilic channel
  14. Peripheral
    a. Not embedded at all; loosely bound to the surface of the membrane, often to exposed parts of integral proteins
  15. iii. On cytoplasmic side, some membrane proteins held in place by attachment to __
    iv. On EC side, attached to fibers of __
    v. These attachments combine to give animal cells a stronger framework than plasma membrane
    • cytoskeleton
    • ECM
  16. Functions of membrane proteins:
    • 1.      Transport: may have hydrophilic channel or shuttle them across; some are pumps powered by ATP
    • 2.      enzymatic: active site exposed to substances of adjacent solution or work as team to carry out sequential steps of pathway
    • 3.      signal transduction: binding site with specific shape that fits shape of chemical messenger, such as hormone, which may cause change in shape, allowing relay of message to inside of cell
    • 4.      cell-cell recognition: recognize ID tags
    • 5.      intercellular joining: may hook together in various junctions (gap, tight) 
    • 6.      attachment to cytoskeleton or ECM: may be noncovalently bound to help maintain cell shape and stabilize location
  17.                                                               i.      Cell-cell recognition
    1.      Ability to__ : crucial
    a.      Sorting of cells into tissues and organs in animal embryo
    b.      Basis for rejection of foreign cells by immune system
    c.       Recognize by binding to molecules
     distinguish one type of cell from another
  18. a.      Membrane __are usually short, branched chains of fewer than __sugar units
                                                                  i.      Some covalently bound to lipids: __
                                                                ii.      Some covalently bound to proteins: __
                                                              iii.      Carbohydrates on EC side vary among species, individuals, and cells
    1.      Diversity of the molecules on surface enable membrane carbohydrates to function as __
    • carbohydrates
    • 15
    • glycolipids
    • glycoproteins
    • markers to distinguish cells
  19. Explain why the membrane has distinct inside and outside faces
    • i. Two lipid layers may have different lipid composition and each protein has directional orientation in membrane
    • ii. Asymmetrical arrangement of proteins, lipids, and associated carbohydrates is determined as membrane ins being built by ER and golgi apparatus