Membrane Components Quiz
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Questions and Answers

What are the main characteristics of integral membrane proteins?

  • They span the entire membrane. (correct)
  • They have only one transmembrane domain.
  • They can be easily removed without disrupting the membrane.
  • They are loosely associated with the membrane.

    • Which factor is associated with peripheral proteins?

  • They interact mainly with the hydrophobic core of the membrane.
  • They have multiple transmembrane domains.
  • They can only be removed by detergents.
  • They are loosely associated with membrane and can be disrupted by high salt. (correct)

    • Which type of integral membrane protein has a single transmembrane helix with the amino-terminal domain outside of the cell?

  • Type III
  • Type I (correct)
  • Type II
  • Type IV

    • What is NOT a feature of amphitropic proteins?

    <p>They are always tightly bound to the membrane.</p> Signup and view all the answers

    How do integral membrane proteins exhibit lateral movement?

    <p>They can move within the lipid bilayer.</p> Signup and view all the answers

    How are transmembrane domains formed in Type V integral proteins?

    <p>They form from the assembly of various polypeptides.</p> Signup and view all the answers

    What does the amphipathic nature of membrane lipids contribute to?

    <p>Formation of a stable lipid bilayer.</p> Signup and view all the answers

    Which statement accurately reflects the function of recognition factors in membranes?

    <p>They assist in the interaction with extracellular fluid (ECF).</p> Signup and view all the answers

    What is a characteristic of membrane dynamics?

    <p>Individual lipids in the membrane undergo fast lateral diffusion.</p> Signup and view all the answers

    Which of the following statements about membrane permeability is correct?

    <p>Membranes are permeable to small polar solutes and nonpolar compounds.</p> Signup and view all the answers

    Which enzyme is NOT involved in the catalysis of transverse diffusion in membranes?

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

    What is required for spontaneous flipping of lipids from one leaflet to another?

    <p>Energetic catalysis by flippases.</p> Signup and view all the answers

    How do flippases typically operate during lipid movement?

    <p>They utilize the energy from ATP to move lipids against a concentration gradient.</p> Signup and view all the answers

    Which property is NOT a physical characteristic of membranes?

    <p>They are composed of rigid structures.</p> Signup and view all the answers

    What primarily holds type IV proteins to the lipid bilayer?

    <p>Covalently linked lipids</p> Signup and view all the answers

    Which type of protein features both transmembrane helices and lipid anchors?

    <p>Type VI</p> Signup and view all the answers

    Which of the following is NOT a function of membrane proteins?

    <p>Energy production</p> Signup and view all the answers

    What is the transition temperature (Tm) related to in membrane fluidity?

    <p>The temperature at which membranes become rigid</p> Signup and view all the answers

    How does the presence of cholesterol affect membrane fluidity when the membrane is already rigid?

    <p>Increases fluidity</p> Signup and view all the answers

    Which of the following statements about fatty acid composition is true?

    <p>Long chain fatty acids decrease fluidity.</p> Signup and view all the answers

    Which of the following molecules serves as a lipid anchor for some membrane proteins?

    <p>Glycosylated phosphatidylinositol (GPI)</p> Signup and view all the answers

    What effect do unsaturated lipids have on membrane fluidity?

    <p>Increase fluidity</p> Signup and view all the answers

    What role do external proteins play in cellular membranes?

    <p>Anchoring the membrane to the cytoskeleton</p> Signup and view all the answers

    What occurs when the temperature exceeds Tm in terms of membrane fluidity?

    <p>Membrane becomes too fluid</p> Signup and view all the answers

    Study Notes

    Membrane Components

    • Phosphatidylethanolamine (PE) and phosphatidylserine (PS) are key components of cell membranes.
    • Membranes interact with extracellular (ECF) and intracellular (ICF) fluids, regulating the movement of polar molecules.

    Types of Membrane Proteins

    • Integral Proteins:
      • Span the entire membrane and exhibit asymmetry.
      • Tightly associated with the membrane; can only be removed by detergents.
      • Capable of lateral movement within the membrane.
    • Peripheral Proteins:
      • Loosely attached to membrane via interactions with polar head groups.
      • Removed by disrupting ionic interactions (e.g., high salt or pH changes).
    • Amphitropic Proteins:
      • Sometimes associated with membranes, bound loosely.

    Types of Integral Membrane Proteins

    • Type I & II: Each has a single transmembrane helix; amino-terminal domain orientation differs between types.
    • Type III: Contains multiple transmembrane helices within a single polypeptide.
    • Type V: Transmembrane domains from different polypeptides combine to form channels.

    Physical Properties of Membranes

    • Membranes are dynamic and flexible, capable of existing in various phases.
    • Not permeable to large polar solutes and ions, while small polar solutes and nonpolar compounds can pass through.

    Membrane Dynamics

    • Transverse Diffusion: Rare spontaneous flips from one leaflet of the membrane to another; lateral diffusion of lipids is fast and requires no catalysis.

    Enzyme-Catalyzed Transverse Diffusion

    • Specialized enzymes (flippases, floppases, scramblases) facilitate lipid movement across the membrane.
    • Some flippases utilize ATP to transport lipids against the concentration gradient.

    Lipid Anchors

    • Some proteins in membranes are considered lipoproteins, containing covalently linked lipid molecules like long-chain fatty acids and isoprenoids.
    • These lipid anchors enable proteins to be reversibly secured to the membrane, allowing for targeted positioning.

    Functions of Membrane Proteins

    • Receptors detect external signals (light, hormones, neurotransmitters).
    • Serve as channels, gates, pumps, and pores facilitating nutrient and ion transport.

    Membrane Attachment to Cytoskeleton

    • Cell membranes anchor to the cytoskeleton, with proteins extending into interstitial spaces to perform functions like self-identification and receptor activities.

    Membrane Fluidity

    • Transition temperature (Tm) determines fluidity:
      • Above Tm, membranes are too fluid; below Tm, they become rigid.
    • Lipid Composition:
      • Long-chain fatty acids decrease fluidity; short-chain fatty acids increase it.
      • Saturated lipids reduce fluidity; unsaturated lipids increase it.
    • Cholesterol:
      • Cholesterol's presence can decrease fluidity in fluid membranes and increase it in rigid membranes.

    Membrane Composition Adaptation

    • Organisms can modify membrane composition primarily through fatty acid adjustments to maintain appropriate fluidity.

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    1_Membrane_structure_LEC_2024.pptx

    Description

    Explore the crucial components of cell membranes, including phosphatidylethanolamine and phosphatidylserine. This quiz will help you understand how these components interact with extracellular fluid and their roles in membrane properties.

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