Membrane Structure and Composition
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Questions and Answers

What is the primary function of the myelin sheath in neurons?

  • Serve as a barrier to pathogens
  • Provide electrical insulation (correct)
  • Facilitate nutrient transport
  • Support cellular structure

    • Which component is found in the plasma membrane but not in the mitochondrial membrane?

  • Cholesterol (correct)
  • Proteins
  • Cardiolipin
  • Phospholipids

    • How do different membranes maintain their unique lipid compositions?

  • Through selective lipid synthesis (correct)
  • By external lipid absorption
  • Via passive diffusion
  • By random lipid incorporation

    • Which lipid is notably absent from the plasma membrane but abundant in the mitochondrial membrane?

    <p>Cardiolipin</p> Signup and view all the answers

    What is true regarding the lipid composition in plasma membranes compared to mitochondrial membranes?

    <p>Plasma membranes contain more cholesterol than mitochondrial membranes</p> Signup and view all the answers

    What characterizes the lipid distribution in plasma membranes?

    <p>Asymmetric lipid distribution</p> Signup and view all the answers

    Which statement correctly relates to membrane protein functions?

    <p>Most enzyme reactions occur in plasma membranes</p> Signup and view all the answers

    What does the absence of cardiolipin in plasma membranes imply?

    <p>Different functional roles compared to mitochondria</p> Signup and view all the answers

    What marks the cell for apoptosis in some cell types?

    <p>Exposure of phosphatidylserine on the outer surface</p> Signup and view all the answers

    Which statement correctly describes the fluid mosaic model?

    <p>Proteins and lipids can move laterally within the bilayer.</p> Signup and view all the answers

    What is the implication of asymmetric orientation of proteins in the bilayer?

    <p>Proteins serve different functions depending on their orientation.</p> Signup and view all the answers

    What is necessary for anchoring a protein to a membrane?

    <p>More than one lipid is usually necessary.</p> Signup and view all the answers

    What is a consequence of changes in lipid distribution?

    <p>It can lead to changes in protein function.</p> Signup and view all the answers

    What happens to the movement of proteins and lipids across the membrane?

    <p>Movement from one face to the other face is restricted.</p> Signup and view all the answers

    What role do integral membrane proteins play in the fluid mosaic model?

    <p>They float within the lipid layer and may have functional roles.</p> Signup and view all the answers

    The fluid mosaic model was proposed in which year?

    <p>1972</p> Signup and view all the answers

    What is the primary role of maltoporin as mentioned in the content?

    <p>Sugar transporter</p> Signup and view all the answers

    What method was used to determine the size of glycophorin in the experiment?

    <p>Denaturing gel electrophoresis</p> Signup and view all the answers

    What enzyme was used to treat erythrocyte membranes in the experiment?

    <p>Trypsin</p> Signup and view all the answers

    What was the result of treating erythrocytes with trypsin concerning glycophorin?

    <p>Glycophorin was approximately 60 residues shorter</p> Signup and view all the answers

    In the context of membrane topology, what does the term 'hydrophilic domain' refer to?

    <p>A part of the protein exposed to the aqueous environment</p> Signup and view all the answers

    How many residues does glycophorin have as an integral protein of the erythrocyte membrane?

    <p>131 residues</p> Signup and view all the answers

    What is the significance of membrane topology in protein studies?

    <p>Shows the localization of the polypeptide chain relative to the membrane</p> Signup and view all the answers

    What might be a reason for a protein's hydrophilic domain to protrude from the membrane?

    <p>To participate in cellular signaling</p> Signup and view all the answers

    What is the role of glycosyl phosphatidyl inositol (GPI) in membrane proteins?

    <p>It helps target a protein to the correct side of the membrane.</p> Signup and view all the answers

    Which statement accurately describes amphitropic proteins?

    <p>Their association with membranes depends on specific regulatory processes.</p> Signup and view all the answers

    What is indicated by a positive hydropathy index for an amino acid?

    <p>It is hydrophobic and tends to seek a non-aqueous environment.</p> Signup and view all the answers

    What does a hydropathy plot represent?

    <p>The hydropathy index plotted against residue number.</p> Signup and view all the answers

    How can one analyze whether a protein is membrane-associated?

    <p>By looking for hydrophobic amino acids in its sequence.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of integral proteins?

    <p>They can easily dissociate from the membrane.</p> Signup and view all the answers

    Why is reversible palmitoylation important for amphitropic proteins?

    <p>It allows proteins to switch between membrane-associated and non-associated states.</p> Signup and view all the answers

    What typically characterizes hydrophilic amino acids in terms of their hydropathy index?

    <p>They have a negative hydropathy index.</p> Signup and view all the answers

    What phenomenon allows the probe tip in atomic force microscopy to interact with membrane proteins?

    <p>Electrostatic interactions</p> Signup and view all the answers

    What can atomic force microscopy visualize with respect to purified membrane proteins?

    <p>Their reconstitution in artificial membranes</p> Signup and view all the answers

    What does the color coding in atomic force microscopy indicate about the distance from the laser?

    <p>Yellow indicates proximity to the laser</p> Signup and view all the answers

    Which statement describes the characteristics of membrane microdomains as visualized by atomic force microscopy?

    <p>They form liquid-ordered 'rafts' in a liquid-disordered membrane.</p> Signup and view all the answers

    What protein mentioned is specifically associated with Halobacterium salinarum in the context of atomic force microscopy?

    <p>Bacteriorhodopsin</p> Signup and view all the answers

    How are membrane proteins inserted in the artificial membrane as indicated in the observations?

    <p>In two possible orientations</p> Signup and view all the answers

    What approximate percentage of some cell surfaces are occupied by membrane microdomains like rafts?

    <p>50%</p> Signup and view all the answers

    What aspect of plasma membranes is suggested by the observation that they are not uniform?

    <p>They have distinct structural domains.</p> Signup and view all the answers

    Study Notes

    Membrane Components

    • All membranes contain lipids and proteins
    • Myelin sheaths of neurons have a higher lipid to protein ratio
    • Plasma membranes of bacteria and mitochondria have a higher protein to lipid ratio
    • Plasma membranes are enriched with cholesterol, but do not contain cardiolipin
    • Mitochondrial membranes are enriched with cardiolipin, but contain less cholesterol
    • Cardiolipin is present in the mitochondria's inner and outer membranes

    Membrane Structure

    • Membranes are asymmetric with different lipid compositions in the inner and outer leaflets
    • The outer leaflet of the plasma membrane contains phosphatidylserine, which is exposed during apoptosis
    • Phosphatidylserine exposure in the outer leaflet marks cells for programmed cell death

    Fluid Mosaic Model

    • Fatty acyl chains in the interior of the membrane form a fluid hydrophobic region
    • Integral membrane proteins float within the lipid bilayer
    • The orientation of proteins within the bilayer is asymmetric
    • Proteins and lipids can move laterally within the plane of the membrane
    • Movement of proteins and lipids between the inner and outer leaflets of the membrane is restricted

    Membrane Proteins

    • Peripheral membrane proteins interact with the membrane through interactions with integral proteins, lipids, or both
    • Integral membrane proteins are embedded within the membrane
    • Amphitropic proteins associate with membranes in a regulated manner

    Hydropathy Plots

    • Hydropathy plots are used to determine the location of transmembrane domains of proteins
    • Hydropathy plots show the hydropathy index plotted against the residue number
    • Hydrophilic amino acids have a negative hydropathy index
    • Hydrophobic amino acids have a positive hydropathy index

    Membrane Topology

    • Membrane topology refers to the location of the polypeptide chain relative to the lipid bilayer
    • Trypsin is an enzyme that cannot cross cell membranes
    • Trypsin cleaves proteins on exposed parts of the protein
    • Glycophorin is a transmembrane protein of red blood cells
    • Glycophorin has a single transmembrane domain with sugar residues on the outer surface of the membrane
    • When red blood cells are treated with trypsin, glycophorin is cleaved on the outer surface, resulting in a smaller protein

    Atomic Force Microscopy

    • Atomic force microscopy can visualize membrane proteins
    • Atomic force microscopy uses a probe that moves up and down based on electrostatic and Van Der Waals interactions with the membrane
    • Atomic force microscopy can be used to visualize purified membrane proteins reconstituted in artificial membranes
    • Atomic force microscopy reveals that membranes are not uniform
    • Atomic force microscopy confirms the existence of membrane microdomains, which are enriched in sphingolipids and cholesterol
    • Microdomains are called rafts and have a liquid-ordered structure, similar to a raft floating on an ocean
    • Rafts can take up to 50% of the cell surface

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    Description

    Explore the intricate details of membrane components and structure in this quiz. Learn about the lipid and protein ratios in various membranes, asymmetry in composition, and the fluid mosaic model. Test your understanding of key concepts related to cell membranes and their functions.

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