Plasma Membrane 1
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Plasma Membrane 1

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Questions and Answers

Which technique is necessary to study the details of the organization of cell membranes?

  • Spectrophotometry
  • Microscopy
  • Centrifugation
  • X-ray diffraction (correct)

    • According to the fluid mosaic model, cell membranes are described as:

  • Fluid, dynamic structures with molecules able to move in the plane of the membrane (correct)
  • Completely impermeable structures
  • Static, rigid structures with fixed molecules
  • Lacking a lipid bilayer structure

    • What is the typical thickness of a plasma membrane as viewed in cross-section?

  • 0.5-0.8 nm
  • 10-15 nm
  • 50-80 nm
  • 5-8 nm (correct)

    • In an electron micrograph of an E.coli cell, what is denoted by the red circle in the schematic of the lipid bilayer?

    <p>Hydrophilic head with a polar phosphoglycerol group</p> Signup and view all the answers

    Which type of structures exclude water as well as polar or charged compounds?

    <p>Hydrophobic barriers</p> Signup and view all the answers

    What is the main characteristic shared by all cell membranes when viewed in cross-section?

    <p>Trilaminar appearance</p> Signup and view all the answers

    What is the main function of cell membranes?

    <p>Regulate movement of materials into and out of the cell</p> Signup and view all the answers

    Which statement best describes the structure of a cell membrane?

    <p>Selectively permeable to polar solutes</p> Signup and view all the answers

    What is the significance of the cell membrane in cell-to-cell communication?

    <p>Facilitates electrical signaling between cells</p> Signup and view all the answers

    Which function is NOT attributed to cell membranes?

    <p>Producing genetic mutations</p> Signup and view all the answers

    Why are cell membranes described as 'selectively permeable'?

    <p>They regulate which molecules can pass based on size and polarity</p> Signup and view all the answers

    In what way do cell membranes contribute to compartmentalization in eukaryotic cells?

    <p>Help separate processes and compartments within the cell</p> Signup and view all the answers

    What is the main function of compartmentalization in cell membranes?

    <p>Separate anabolic and catabolic processes</p> Signup and view all the answers

    Which organelles are involved in fatty acid oxidation for energy production?

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

    What is the main role of proteins in cell membranes?

    <p>Facilitate transport across the membrane</p> Signup and view all the answers

    Which component makes up about 50% of the mass of most animal cell membranes?

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

    Where are the TCA cycle and electron transport chain located in a cell?

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

    Which type of cations are commonly found associated with cell membranes?

    <p>$Ca^{2+}$ and $Mg^{2+}$</p> Signup and view all the answers

    What is the main difference between prokaryotic and eukaryotic plasma membranes?

    <p>Eukaryotic membranes are composed of different types of phospholipids, while prokaryotic membranes are composed of a single type.</p> Signup and view all the answers

    What role do sterols like cholesterol play in the stability and fluidity of cell membranes?

    <p>Increase both mechanical stability and fluidity.</p> Signup and view all the answers

    What is the purpose of membrane fusion in cellular processes?

    <p>To allow for the transport of material between organelles and the plasma membrane.</p> Signup and view all the answers

    How do lipid molecules assemble in aqueous environments?

    <p>With hydrophobic tails in the interior and hydrophilic heads outside to water.</p> Signup and view all the answers

    What is the significance of membrane fission in cellular processes?

    <p>To enable the splitting of a membrane into two parts for transport purposes.</p> Signup and view all the answers

    How do hydrophilic molecules behave in aqueous environments?

    <p>They dissolve readily in water due to uncharged polar groups that interact favorably with water molecules.</p> Signup and view all the answers

    Why does phospholipid bilayer closure to form a sealed compartment represent an energetically favorable process?

    <p>The closed structure prevents the exposure of hydrophobic tails to water, which is energetically unfavorable.</p> Signup and view all the answers

    In an aqueous environment, which type of molecules form micelles according to the text?

    <p>Fatty acids</p> Signup and view all the answers

    What is the main difference between vesicles and liposomes as outlined in the text?

    <p>Vesicles are naturally occurring, while liposomes are artificial structures created in laboratories.</p> Signup and view all the answers

    What is the function of vesicles within cells as described in the text?

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

    Which technique directly produces a three-dimensional image of the surface of a specimen according to the text?

    <p>Scanning electron microscopy (SEM)</p> Signup and view all the answers

    Why do phospholipids form bilayers or liposomes according to the text?

    <p>Their cylinder-shaped form leads to bilayer or liposome formation.</p> Signup and view all the answers

    What is the main function of the cell membrane in facilitating electrical signaling between cells?

    <p>Serving as an attachment surface</p> Signup and view all the answers

    Which type of cells break and re-seal their cell membranes for fusion or fission?

    <p>Eukaryotic cells</p> Signup and view all the answers

    How do cell membranes contribute to the regulation of molecular traffic across the boundary?

    <p>By being selectively permeable</p> Signup and view all the answers

    What is the primary role of the lipid bilayer structure in the cell membrane?

    <p>Providing a barrier to separate cellular compartments</p> Signup and view all the answers

    Which visualization technique is commonly used to study the details of the organization of cell membranes?

    <p>Electron microscopy</p> Signup and view all the answers

    What is the significance of the compartmentalization provided by cell membranes in eukaryotic cells?

    <p>Segregating processes and compartments</p> Signup and view all the answers

    What type of structures are cell membranes, as described in the text?

    <p>Fluid and dynamic</p> Signup and view all the answers

    Which component makes up the central region in the trilaminar appearance of cell membranes when viewed in cross-section?

    <p>Hydrophilic heads</p> Signup and view all the answers

    What does the red circle in the schematic of the lipid bilayer denote?

    <p>Hydrophilic head</p> Signup and view all the answers

    Why is membrane thickness important in influencing the rate of diffusion across cell membranes?

    <p>Thinner membranes allow for faster diffusion.</p> Signup and view all the answers

    What characteristic appearance do all cell membranes share when viewed in cross-section?

    <p>Trilaminar appearance</p> Signup and view all the answers

    Which technique is necessary to study the details of the organization of cell membranes as implied in the text?

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

    Why does the spontaneous closure of a phospholipid bilayer to form a sealed compartment represent an energetically favorable process?

    <p>It prevents the exposure of the hydrophobic hydrocarbon tails to water, which is energetically unfavorable.</p> Signup and view all the answers

    Which type of molecules form micelles in an aqueous environment according to the text?

    <p>Amphipathic molecules</p> Signup and view all the answers

    What is the main difference between vesicles and liposomes?

    <p>Vesicles consist of liquid enclosed by a lipid bilayer, while liposomes consist of cytoplasm enclosed by a lipid bilayer.</p> Signup and view all the answers

    What is the role of lipids in forming vesicles and bilayers?

    <p>Lipids spontaneously form vesicles and bilayers due to their amphipathic nature.</p> Signup and view all the answers

    What is the significance of vesicles in cellular processes?

    <p>Vesicles are involved in temporary storage, transport, and metabolic processes within cells.</p> Signup and view all the answers

    How do liposomes differ from vesicles?

    <p>Liposomes consist of liquid enclosed by a lipid bilayer, while vesicles consist of cytoplasm enclosed by a lipid bilayer.</p> Signup and view all the answers

    What does the freeze-fracture technique involve?

    <p>Breaking apart a frozen biological sample to study the membrane</p> Signup and view all the answers

    How do differences in the length and saturation of fatty acid tails affect phospholipid molecules?

    <p>Enhance the ability to pack together and influence membrane fluidity</p> Signup and view all the answers

    What is the main structural difference between saturated and unsaturated fatty acids in cell membranes?

    <p>The presence of double bonds in unsaturated fatty acids</p> Signup and view all the answers

    Which major phospholipids predominate in the plasma membrane of many mammalian cells?

    <p>Phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, sphingomyelin</p> Signup and view all the answers

    Why is the freeze-fracture technique important for studying cell membranes?

    <p>It reveals internal membrane organization by fracturing frozen samples</p> Signup and view all the answers

    How does the freeze-etch electron microscopy technique differ from freeze-fracture?

    <p>It creates a 3D view of surfaces inside cells by etching frozen samples</p> Signup and view all the answers

    What is the main purpose of compartmentalization in cell membranes?

    <p>Avoiding interference in reactions</p> Signup and view all the answers

    Where are fatty acid oxidation for energy production and fatty acid synthesis held to avoid competition?

    <p>Mitochondria and ER</p> Signup and view all the answers

    Which component makes up approximately 50% of the mass of most animal cell membranes?

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

    Where are the TCA cycle and electron transport chain located to ensure energy efficiency?

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

    How do cell membranes contribute to cell-to-cell communication?

    <p>By facilitating the exchange of signaling molecules</p> Signup and view all the answers

    What is the significance of proteins in biological membranes?

    <p>To interact with other molecules and transport materials</p> Signup and view all the answers

    What type of model describes cell membranes as fluid, dynamic structures where most molecules can move?

    <p>Fluid mosaic model</p> Signup and view all the answers

    In the trilaminar appearance of all cell membranes, what do the two electron-dense layers consist of?

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

    What is the main function of the hydrophilic head denoted by the red circle in the schematic of the lipid bilayer?

    <p>Attract water and charged compounds</p> Signup and view all the answers

    What is the significance of the less dense central region in the trilaminar appearance of cell membranes?

    <p>Facilitates movement of transmembrane proteins</p> Signup and view all the answers

    What technique is necessary to study the detailed organization of cell membranes and involves breaking them to reveal their inner structures?

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

    In what way does membrane thickness influence the rate of diffusion across cell membranes?

    <p>Thicker membranes impede diffusion</p> Signup and view all the answers

    What is the main function of the plasma membrane in a cell according to the text?

    <p>Facilitating electrical signaling between cells</p> Signup and view all the answers

    Why are cell membranes described as 'selectively permeable'?

    <p>To only permit certain molecules to cross while blocking others</p> Signup and view all the answers

    Which component plays a central role in defining the external boundaries of a cell?

    <p>Membrane lipids</p> Signup and view all the answers

    How do cell membranes contribute to biological energy conservation?

    <p>By facilitating electron transport chain reactions</p> Signup and view all the answers

    What is a key feature of the lipid bilayer structure in cell membranes?

    <p>Providing flexibility and selective permeability</p> Signup and view all the answers

    Which major function of cell membranes involves serving as an attachment surface for extracellular structures?

    <p>Providing attachment points for cytoskeleton proteins</p> Signup and view all the answers

    Why is the closure of a phospholipid bilayer to form a sealed compartment energetically favorable?

    <p>It stabilizes the closed structure by avoiding exposure of hydrophobic tails to water.</p> Signup and view all the answers

    What is the main difference between micelles and bilayers according to the text?

    <p>Micelles are cone-shaped, while bilayers are cylinder-shaped.</p> Signup and view all the answers

    In cell membranes, what provides the self-healing property to the bilayer?

    <p>Free edges</p> Signup and view all the answers

    What is the purpose of vesicles within cells as described in the text?

    <p>To have cytoplasm with different composition from the cytosol</p> Signup and view all the answers

    How do liposomes differ from vesicles according to the text?

    <p>Liposomes consist of liquid/cytoplasm enclosed by a lipid bilayer, while vesicles are intra or extra cellular structures.</p> Signup and view all the answers

    What is the main function of lipids in forming vesicles and bilayers?

    <p>To provide stability and enclosure</p> Signup and view all the answers

    What is the main function of transmembrane proteins in cell membranes?

    <p>Serve as structural links between the cytoskeleton and the extracellular matrix</p> Signup and view all the answers

    Which statement accurately describes the lipid bilayer in cell membranes?

    <p>Consists of amphipathic lipid molecules</p> Signup and view all the answers

    What is the significance of membrane proteins in drug development?

    <p>They serve as targets for over 50% of modern medicinal drugs</p> Signup and view all the answers

    Which lipid molecule is the most abundant in cell membranes?

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

    What is the primary reason for the bilayer structure of cell membranes?

    <p>Due to special properties of lipids that cause spontaneous assemblage into bilayers</p> Signup and view all the answers

    Why are over 30% of human genome's proteins classified as membrane proteins?

    <p>To facilitate signal transduction and proper cell function</p> Signup and view all the answers

    How does the freeze-fracture technique help in studying cell membranes?

    <p>It physically breaks apart frozen biological samples to expose structural detail</p> Signup and view all the answers

    What is the function of the polar head group in phospholipids?

    <p>To anchor the phospholipid in the membrane</p> Signup and view all the answers

    How do differences in the length and saturation of fatty acid tails affect membrane fluidity?

    <p>They affect the ability of phospholipid molecules to pack together and guarantee membrane fluidity</p> Signup and view all the answers

    What is the significance of coating the fractured surface with a metal layer in freeze-fracture electron microscopy?

    <p>To provide contrast for electron microscopy</p> Signup and view all the answers

    What makes up more than half of the lipid mass in most cell membranes?

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

    What role do unsaturated fatty acids play in phospholipids compared to saturated fatty acids?

    <p>Create small kinks in the fatty acid tails</p> Signup and view all the answers

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