Membrane Structure and Function
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Questions and Answers

What triggers the phosphorylation of the sodium-potassium pump?

  • High concentration of Na+ outside the cell
  • Release of ADP
  • Binding of K+ to the pump
  • Binding of Na+ to the pump (correct)

    • During the function of the sodium-potassium pump, what occurs after Na+ is expelled from the cell?

  • K+ binds to the protein and restores its original conformation (correct)
  • The pump remains inactive until K+ is removed
  • ADP releases another phosphate group
  • Na+ can bind to the pump again immediately

    • What is the initial condition of the sodium and potassium concentrations before the pump operates?

  • [Na+] is low in the cytoplasm and [K+] is also low
  • [Na+] and [K+] are both balanced across the membrane
  • [Na+] is high outside the cell and [K+] is low in the cytoplasm (correct)
  • [Na+] is low in the cytoplasm and [K+] is high outside the cell

    • What is the role of ATP in the sodium-potassium pump mechanism?

    <p>It provides energy for phosphorylation.</p> Signup and view all the answers

    What happens to the sodium-potassium pump when K+ binds to the extracellular side?

    <p>The protein's conformation changes, leading to the release of phosphate.</p> Signup and view all the answers

    What is the primary function of receptors in receptor-mediated endocytosis?

    <p>To select specific extracellular compounds</p> Signup and view all the answers

    What triggers the formation of vesicles during receptor-mediated endocytosis?

    <p>Binding of ligands to receptors</p> Signup and view all the answers

    Which component is likely involved in the formation of coated pits during receptor-mediated endocytosis?

    <p>Coat proteins</p> Signup and view all the answers

    What term describes a molecule that binds specifically to a receptor molecule in receptor-mediated endocytosis?

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

    In receptor-mediated endocytosis, what is the role of the coated vesicle?

    <p>To transport specific compounds into the cell</p> Signup and view all the answers

    What structural feature distinguishes endocytosis as receptor-mediated?

    <p>Presence of coated pits</p> Signup and view all the answers

    How do ligands enter the cell during receptor-mediated endocytosis?

    <p>Through vesicles formed by receptor-ligand binding</p> Signup and view all the answers

    What is the significance of ligand-receptor binding in receptor-mediated endocytosis?

    <p>It initiates vesicle formation</p> Signup and view all the answers

    What is the primary function of the CTR-1 protein?

    <p>Absorbing copper in intestinal epithelial cells</p> Signup and view all the answers

    What type of genetic inheritance pattern is associated with CTR-1 deficiency?

    <p>Autosomal recessive</p> Signup and view all the answers

    What is the result when water moves from a hypotonic solution to a hypertonic solution?

    <p>An isotonic equilibrium is reached</p> Signup and view all the answers

    What can be a symptom of CTR-1 deficiency?

    <p>Severe developmental delay</p> Signup and view all the answers

    Which of the following best describes osmosis?

    <p>Movement of water through a semipermeable membrane</p> Signup and view all the answers

    What is the primary role of the proton pump in the cotransport process?

    <p>To maintain a higher concentration of H+ outside the cell</p> Signup and view all the answers

    In the example of cotransport described, what energy source is used to maintain the H+ gradient?

    <p>Energetic ATP hydrolysis</p> Signup and view all the answers

    How does the sucrose-H+ cotransporter function in this transport mechanism?

    <p>It relies on the potential energy of the H+ gradient to import sucrose</p> Signup and view all the answers

    What type of transport is represented by the movement of H+ through the proton pump?

    <p>Active transport</p> Signup and view all the answers

    What happens to the gradient of H+ ions when ATP is utilized by the proton pump?

    <p>The gradient is maintained, keeping H+ concentration high outside the cell</p> Signup and view all the answers

    What is the ultimate benefit of the H+ gradient established by the proton pump?

    <p>To create potential energy that drives the cotransport of sucrose</p> Signup and view all the answers

    Which process describes the movement of H+ ions into the cell through diffusion?

    <p>Passive transport</p> Signup and view all the answers

    Why is the transport of sucrose dependent on the movement of H+ ions?

    <p>The energy from H+ movement allows sucrose to be transported against its gradient</p> Signup and view all the answers

    Which of the following descriptions correctly defines phagocytosis?

    <p>The mechanism by which cells take in solid particles or bacteria.</p> Signup and view all the answers

    What is the role of pseudopodia in phagocytosis?

    <p>To aid in the movement and engulfing of particles.</p> Signup and view all the answers

    How does pinocytosis differ from phagocytosis?

    <p>Pinocytosis is the uptake of fluids, while phagocytosis is focused on solid particles.</p> Signup and view all the answers

    What size range do phagocytosis and pinocytosis generally involve for the particles being engulfed?

    <p>Phagocytosis typically deals with particles in the micrometer range, while pinocytosis deals with sub-micrometer particles.</p> Signup and view all the answers

    In which cellular process would one expect to see vesicles forming at the plasma membrane?

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

    What is the primary requirement for active transport to occur?

    <p>It requires energy, usually in the form of ATP.</p> Signup and view all the answers

    Which of the following describes the direction of substance movement in active transport?

    <p>From low concentration to high concentration.</p> Signup and view all the answers

    What type of membrane proteins are primarily responsible for active transport?

    <p>Ion pumps.</p> Signup and view all the answers

    What effect does active transport have on the concentration gradients within cells?

    <p>It maintains concentration gradients that differ from surroundings.</p> Signup and view all the answers

    Which of the following is a specific type of active transport system?

    <p>Sodium-potassium (Na+/K+) pump.</p> Signup and view all the answers

    Which of the following correctly distinguishes active transport from passive transport?

    <p>Active transport requires energy to move substances against a gradient.</p> Signup and view all the answers

    What is the role of ATP in active transport?

    <p>To provide energy necessary for transport.</p> Signup and view all the answers

    Active transport primarily functions to:

    <p>Allow cells to control internal concentrations of substances.</p> Signup and view all the answers

    Study Notes

    Membrane Structure and Function

    • The plasma membrane separates the living cell from its non-living surroundings
    • The plasma membrane is a fluid mosaic of lipids and proteins
    • The fluid mosaic model was proposed by Singer and Nicolson in 1972
    • The membrane is a fluid structure with a "mosaic" of various proteins embedded within it
    • The membrane is composed of a phospholipid bilayer and proteins embedded within it
    • Phospholipids are amphipathic, consisting of hydrophilic "heads" and hydrophobic "tails"
    • Phospholipids spontaneously create bilayers in an aqueous environment
    • Phospholipids form micelles or liposomes in aqueous environments
    • Micelles are single-layer spherical structures
    • Liposomes are bilayer spherical structures, used for efficient delivery of drugs/compounds to cells
    • Membrane lipids include phospholipids, glycolipids, and sterols
    • Phospholipids can be either phosphoglycerides or phosphosphingolipids
    • Phosphoglycerides are based on glycerol + 2 fatty acids + phosphate + organic molecule
    • Phosphosphingolipids are based on sphingosine + 1 fatty acid + phosphate + organic molecule
    • Cholesterol, a steroid alcohol, is found in animal cell membranes
    • Phytosterols are found in plant cell membranes
    • Ergosterol is found in fungal and protozoal cell membranes
    • Membrane proteins determine most of the membrane's functions
    • These proteins are embedded within the lipid bilayer
    • Membrane proteins come in integral and peripheral types
    • Integral proteins completely span the membrane, or are attached to a membrane lipid
    • Peripheral proteins are loosely bound to the membrane
    • Integral transmembrane proteins span the cell membrane one or more times
    • This type of protein penetrates the hydrophobic core of the lipid bilayer
    • Examples of transmembrane proteins are growth factor receptors (EGFR), insulin, ẞ-barrel: e.g. bacterial porin
    • Lipid-bound proteins are attached to a membrane lipid
    • Examples of lipid-bound proteins are hydrolases, receptors
    • Peripheral membrane proteins are loosely bound to the membrane and interact with the polar surface of the membrane or with proteins imbedded in the membrane
    • Examples of peripheral proteins are erythrocyte spectrin
    • Transmembrane proteins can have various functions including transportation, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to the cytoskeleton and extracellular matrix
    • Membrane carbohydrates include glycoproteins, glycolipids, and proteoglycans
    • Glycocalyx is the carbohydrate cover on the external side of the cell membrane, protecting the cell surface from mechanical/chemical damage
    • The human blood cell types A, B, AB, and O reflect variation in RBC surface carbohydrates There are 2 types of passive transport: diffusion and osmosis
    • Diffusion is the tendency of any substance to spread out evenly in the available space
    • Active transport moves substances against their concentration gradient, and requires energy often in the form of ATP
    • Cells can maintain concentration gradients that differ from their surroundings
    • Active transport is performed by specialized membrane proteins, called ion pumps
    • The sodium-potassium pump (Na+/K+) is one example
    • Osmosis is the movement of water across a semipermeable membrane
    • Osmosis is affected by the concentration gradient
    • Water molecules will move from an area of low solute / higher water concentration to an area with a higher solute / lower water concentration
    • Three conditions can describe osmosis which are isotonic, hypertonic, and hypotonic
    • The term isotonic means that the concentration of solutes in the solution is the same as it is inside the cell and there will be no net movement of water
    • The term hypertonic means that the concentration of solutes in the solution is greater than in the cell, and the cell will lose water
    • The term hypotonic means that the concentration of solutes in the solution is less than in the cell, and the cell will gain water
    • Three examples of bulk transport are phagocytosis, pinocytosis, and receptor-mediated endocytosis
    • In phagocytosis a cell engulfs a solid particle (macromolecule or microorganism) in a vacuole, which fuses with a lysosome
    • Phagocytes are specialized immune cells that can engulf microorganisms
    • In pinocytosis, soluble molecules enter the cell when extracellular fluid is taken up into tiny vesicles
    • Receptor-mediated endocytosis is a type of endocytosis in which specific molecules are taken up when a binding ligand to a receptor triggers vesicle formation, for example the process of cholesterol uptake by hepatocytes

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