Membrane Structures Theories and Models
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Questions and Answers

Which scientist proposed the lipid bilayer model that includes proteins adhering to lipid-aqueous interfaces?

  • Gorter and Grendell
  • Danielli and Davson (correct)
  • Overton
  • Robertson

    • What is the main role of liposomes in biological studies?

  • To provide a source of energy
  • To act as carriers for molecules (correct)
  • To act purely as structural components
  • To enhance lipid solubility

    • In the unit membrane model proposed by Robertson, what comprises the central layer of plasma membranes?

  • Glycerophospholipids only
  • Proteins only
  • Hydrocarbon chains of lipids (correct)
  • Hydrocarbon chains of proteins

    • What does the fluid mosaic model recognize about the arrangement of lipids and proteins?

    <p>They are in a mosaic arrangement with movement</p> Signup and view all the answers

    Which of the following is NOT a major function of lipids?

    <p>Structural support</p> Signup and view all the answers

    What type of molecules can form channels for ions in membranes?

    <p>Certain proteins or polypeptides</p> Signup and view all the answers

    Which component is NOT part of glycerophospholipids?

    <p>Three fatty acyl tails</p> Signup and view all the answers

    Which statement is true regarding the nonpolar/hydrophobic regions of integral proteins?

    <p>They are embedded inside the lipid bilayer</p> Signup and view all the answers

    What is the primary function of the nucleolus?

    <p>Assembly of ribosomal subunits</p> Signup and view all the answers

    Which structure surrounds the nucleolus and is formed of newly transcribed ribosomal RNA?

    <p>Pars fibrosa</p> Signup and view all the answers

    What significant change occurs in the Rdna intergenic region during the evolution from anamniotes to amniotes?

    <p>It increases in size</p> Signup and view all the answers

    How can the Nucleolus Organizer Region (NOR) be identified in a cell?

    <p>By karyotype analysis with silver nitrate staining</p> Signup and view all the answers

    Which of the following is NOT a function of the nucleolus?

    <p>Transcription of DNA</p> Signup and view all the answers

    What property of membranes makes them highly selective barriers?

    <p>Impermeability to ions and most polar molecules</p> Signup and view all the answers

    What is the role of liposomes in biological research?

    <p>To act as vehicles for delivering chemicals to cells</p> Signup and view all the answers

    Which of the following accurately describes the function of channels and pumps in membranes?

    <p>They act as selective transport systems.</p> Signup and view all the answers

    What effect do cis double bonds have on membrane fluidity?

    <p>They disrupt ordered packing and increase fluidity.</p> Signup and view all the answers

    How does the length and saturation of hydrocarbon chains affect membrane fluidity?

    <p>Longer and more saturated chains create a more ordered and rigid membrane.</p> Signup and view all the answers

    What is electrical polarization of a plasma membrane typically at rest?

    <p>-60 millivolts</p> Signup and view all the answers

    What happens to the lipid bilayer above the transition temperature?

    <p>It undergoes a phase change to a more fluid state.</p> Signup and view all the answers

    What is one of the key functions of membranes in terms of energy conversion?

    <p>They organize reaction sequences and enzyme arrays.</p> Signup and view all the answers

    What is the primary mechanism for the bulk ingestion of solid materials by cells?

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

    Which type of endocytosis is induced by proteins, amino acids, and certain ions?

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

    What role does ATP play in the process of endocytosis?

    <p>It increases the rate of endocytosis.</p> Signup and view all the answers

    Which cells primarily perform phagocytosis as a defense mechanism?

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

    What is the structure that separates the two membranes of the nuclear envelope?

    <p>Perinuclear space</p> Signup and view all the answers

    What is the diameter of the nuclear pore complex (NPC)?

    <p>100 nm</p> Signup and view all the answers

    What is the function of the fibrous lamina associated with the inner membrane of the nuclear envelope?

    <p>It maintains the shape of the nucleus.</p> Signup and view all the answers

    Which types of molecules can freely pass through the nuclear pore complex?

    <p>Water and metabolites</p> Signup and view all the answers

    What is the approximate maximum mass of macromolecules that can passively diffuse across the nuclear pore complex (NPC)?

    <p>60 kDa</p> Signup and view all the answers

    What are the nuclear localization sequences (NLSs) necessary for?

    <p>Import of proteins into the nucleus</p> Signup and view all the answers

    Which of the following is considered a cargo for export from the nucleus?

    <p>Ribosomal subunits</p> Signup and view all the answers

    What do the filaments of the nuclear basket help to extend into?

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

    Which of the following describes the primary function of the nucleolus?

    <p>Synthesis of ribosomal RNAs</p> Signup and view all the answers

    What is a characteristic component of the nucleolus that stains lightly?

    <p>Fibrillar centers</p> Signup and view all the answers

    Which transport factor is also known as CRM1?

    <p>XPO1</p> Signup and view all the answers

    What role does turgor pressure play in plants?

    <p>It provides mechanical support for non-woody tissues.</p> Signup and view all the answers

    Which component of the nucleolus is not primarily responsible for rRNA synthesis?

    <p>Cytoplasmic granules</p> Signup and view all the answers

    Which correctly describes water potential in plants?

    <p>It is the tendency of water to move to more negative areas.</p> Signup and view all the answers

    How does active transport differ from passive transport?

    <p>Active transport requires energy, while passive transport does not.</p> Signup and view all the answers

    What is the main source of energy for active transport in cells?

    <p>ATP generated during respiration.</p> Signup and view all the answers

    Which example illustrates passive transport?

    <p>Diffusion of oxygen across a lipid bilayer.</p> Signup and view all the answers

    Facilitated diffusion requires which of the following?

    <p>Specific membrane proteins.</p> Signup and view all the answers

    What conditions apply to water movement based on water potential?

    <p>Water moves to areas with higher solute concentration.</p> Signup and view all the answers

    Which of the following correctly defines pressure potential?

    <p>It represents the force exerted by the cell wall.</p> Signup and view all the answers

    Study Notes

    Theories on Membrane Structures

    • 1902, membranes were thought to consist only of lipids (Overton)
    • 1926, Gorter and Grendell proposed that lipids form a double layer
    • 1935, Danielli and Davson proposed a lipid bilayer model including proteins adhering to both lipid-aqueous interfaces
    • Artificial model systems (liposomes) supported the Danielli-Davson model
    • Droplets of lipid in organic solvent can be spread over a small hole to study biophysical properties of a bilayer (e.g. permeability and electrical resistance)
    • Channels for ions can be formed by adding proteins or polypeptides
    • Liposomes are effective carriers for molecules like chemotherapy drugs, insulin, and antibodies

    Unit Membrane Model

    • Robertson (1959) proposed the unit membrane model
    • This model suggests the central layer of plasma membranes is made up of lipid hydrocarbon chains, with proteins forming dense surrounding layers
    • A simplified model, as it cannot account for the number of proteins across membranes

    Fluid Mosaic Model

    • Singer and Nicolson (1972) proposed the fluid mosaic model
    • The model describes lipids and proteins in a mosaic arrangement
    • Lipids and proteins can move laterally within the lipid bilayer
    • Non-covalent interactions create a fluid-like state for membranes

    Key Concepts

    • Major functions of lipids: energy storage, membrane components
    • Other functions of lipids: signals, electron carriers, emulsifying agents
    • Membrane lipids (amphipathic): responsible for the spontaneous formation of lipid bilayers
    • Glycerophospholipids: glycerol backbone + 2 fatty acyl tails + polar head group
    • Sphingolipids: sphingosine backbone + fatty acid chain + carbohydrate or phosphate ester
    • Cholesterol: affects membrane fluidity
    • Membrane fluidity depends on lipid composition (chain length, double bonds, cholesterol content)

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    Description

    Explore the evolution of theories regarding membrane structures from the early 1900s to modern models. This quiz covers significant contributions by scientists such as Overton, Gorter, Grendell, Danielli, Davson, and Robertson. Test your knowledge on lipid bilayers and their applications in biophysics and medicine.

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