Chapter 12.4

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  1. • Membrane lipids form a __ and thereby establish __, whereas specific proteins __; they __
    o Membrane lipids create the appropriate environment for the action of such proteins
    • permeability barrier
    • compartments
    • mediate all other membrane functions
    • transport chemicals and info across a membrane
  2. • Membranes differ in __; percentages range

    o The protein components of the membrane can be visualized by __ because membranes performing different functions contain __
    • The ease with which a protein can be dissociated from a membrane indicates what? 
    Some can be solubilized by mild means. Others are bound more tenaciously.

    There are __ and __ due to this.
    • protein content
    • SDS-PAGE
    • different repertoires of proteins
    • how intimately it is associated with the membrane

    peripheral and integral
  3. Integral proteins
    interact extensively with the hydrocarbon chains of membrane lipids and can be released only by agents that compete for these nonpolar interactions; span the lipid bilayer
  4. Peripheral
    membrane proteins are bound to membranes by electrostatic and hydrogen-bond interactions with the head groups of lipids; can be disrupted by adding salts or change in the pH; bound to the surfaces of integral proteins, on either the cytoplasmic or extracellular side; others are anchored to the lipid bilayer by a covalently attached hydrophobic chain
  5. • Proteins can span the membrane with __

    o __uses light energy to transport protons from insde to outside the cell, generating a proton gradient used to form bacteria
    • alpha helices
    • Bacteriorhodopsin
  6. Structure of bacteriorhodopsin
    built almost entirely of alpha helices; seven closely packed alpha helices, arranged almost perpendicularly to the place of the cell membrane; mostly nonpolar amino acids allowing contact with the hydrocarbon core of the membrane or with one another

    • Membrane spanning alpha helices are the most common structural motif in membrane proteins
  7. • A channel protein can be formed from __, like __, located in the outer membranes of bacteria; have essentially no __

    Arrangement of beta strands is simple: __
    • beta strands
    • porin
    • alpha heliceso

    each strand is hydrogen bonded to its neighbor in an antiparallel arrangement, forming a single beta sheet, which curls up to form a hollow cylinder that forms a pore in the membrane
  8. The outside surface of porin is __ and the inside is __ and __
    • This arrangement of nonpolar and polar surfaces is accomplished by the __
    • nonpolar
    • hydrophilic and filled with water
    • alternation of hydrophobic and hydrophilic amino acids along each beta strand
  9. • Embedding part of a protein in a membrane can do what, such as is the case with __, which catalyzes the conversion of arachidonic acid into prostaglandin H2

    o Prostaglandin H2 promotes __and modulates __; and the enzyme that produces it is a __with mostly __
    • link the protein to the membrane surface
    • prostaglandin H2 synthase-1
    • inflammation 
    • gastric acid secretion
    • homodimer 
    • alpha helices
  10.  Prostaglandin H2 is not __but instead lies along the __, firmly bound by a set of __ with __ that extend from the bottom of the protein into the membrane

    • This linkage is so strong that what; it is classified as an __, although it does not span the membrane
    • largely embedded in the membrane 
    • outer surface of the membrane
    • alpha helices with hydrophobic surfaces

    only the action of detergents can release the protein from the membrane

    integral membrane protein
  11. o The localization of __is crucial to its function

     The substrate, __, is a hydrophobic molecule generated by __; __ reaches the active site of the enzyme from the membrane without entering an aqueous environment by doing what?
    prostaglandin H2 synthase-1 

    arachidonic acid

    hydrolysis of membrane lipids

    arachidonic acid

    traveling through a hydrophobic channel in a protein
  12. • The parts of the protein that interact with the hydrophobic parts of the membrane are coated with __, whereas those parts that interact with the aqueous environment are much more __•
    The structures positioned within the membrane are quite __and, in particular, all backbone __ participate in __
    o Breaking a hydrogen bond within a membrane is quite unfavorable because __
    • nonpolar amino acid side chains
    • hydrophilic
    • regular 
    • hydrogen-bond donors and acceptors
    • hydrogen bonds
    • little or no water is present to compete for the polar groups
  13. • Some proteins associate with membranes through __

    Soluble proteins can associate with membranes if __.

    Some examples are:
    ---> A __ attached to a specific __residue by a __
    --> A __ attached to a __residue at the __
    --> A __ attached to the __.
    covalently attached hydrophobic groups

    • hydrophobic groups are attached to the proteins
    • palmitoly group
    • cysteine 
    • thioester bond
    • farnesyl group
    • cysteine 
    • carboxyl terminus
    • glycolipid structure termed a glycosylphosphatidylinositol (GPI anchor)
    • carboxyl terminus
  14. o These modifications are attached by __ that recognize __ near the __
    • enzyme systems
    • specific signal sequences
    • site of attachment
  15. • __ can be accurately predicted from amino acid sequences
    o Many membrane proteins employ __ to do what?

    We can identify transmembrane helices by asking what?
    • Transmembrane helices
    • alpha helices
    • span the hydrophobic part of a membrane
    • whether it is likely to be more stable in a hydrocarbon environment or in water, estimating the free-energy change when a helical segment is transferred from the interior of a membrane to water
  16. • The hydrocarbon core of a membrane is about __ wide, a length that can be traversed by an __

    We can estimate the __that takes place when a __ is transferred from the __ to __
    • 30 angstroms
    • alpha helix consisting of 20 residues
    • free-energy change 
    • hypothetical alpha helix formed of residues 1 through 20
    • membrane interior to water
  17. o The span of 20 residues chosen for this calculation is called a __; and the free-energy change for each window is plotted against the first amino acid at the window to create a __

     A peak of __ or more in a __ based on a window of 20 residues indicates that a polypeptide segment could be a __

     Yet, some membrane proteins contain __ that escape detection by these plots
    • window
    • hydropathy plot
    • +84 kJ mol-1
    • hydropathy plot
    • membrane-spanning helix
    • membrane-spanning features
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Chapter 12.4
2014-11-06 20:59:18
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