Cell Biology and Signalling: Membrane Transport
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Questions and Answers

Which glucose transporter has a high Km and is involved in regulating blood glucose levels?

  • GLUT1
  • GLUT2 (correct)
  • GLUT4
  • GLUT3

    • What is the effect of insulin on GLUT4 in muscle and adipose cells?

  • Insulin increases the amount of GLUT4 in the plasma membrane (correct)
  • Insulin only affects GLUT2
  • Insulin has no effect on GLUT4
  • Insulin decreases the amount of GLUT4 in the plasma membrane

    • What type of ion channels are gated by acetylcholine?

  • Ligand-gated channels (correct)
  • Mechanically-gated channels
  • Gap junctions
  • Voltage-gated channels

    • What is the characteristic of GLUT3?

    <p>Low Km and low capacity</p> Signup and view all the answers

    What is the effect of insulin on glucose uptake in muscle and adipose cells?

    <p>Insulin increases glucose uptake</p> Signup and view all the answers

    What is the location of GLUT4 before insulin stimulation?

    <p>Vesicles in the cytoplasm</p> Signup and view all the answers

    Which of the following molecules can freely cross the membrane by simple diffusion?

    <p>Small uncharged or hydrophobic molecules</p> Signup and view all the answers

    What is the primary function of the Na+/K+-ATPase membrane pump?

    <p>To regulate ion concentrations across the membrane</p> Signup and view all the answers

    Which of the following is NOT an example of facilitated diffusion?

    <p>Simple passive transport of O2</p> Signup and view all the answers

    What is the relationship between the partition coefficient of a solute and its rate of diffusion?

    <p>Solute with higher partition coefficient diffuses faster</p> Signup and view all the answers

    What is the function of the GLUT1 glucose transporter?

    <p>To facilitate glucose transport with high affinity (low Km)</p> Signup and view all the answers

    What is the primary difference between passive transport and facilitated diffusion?

    <p>Facilitated diffusion requires a membrane protein, while passive transport does not</p> Signup and view all the answers

    What is the unit of measurement for the partition coefficient of a solute?

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

    Which of the following is an example of secondary active transport?

    <p>None of the above</p> Signup and view all the answers

    What is the relationship between the Km of a transporter and its affinity for the solute?

    <p>Lower Km indicates higher affinity</p> Signup and view all the answers

    What is the primary difference between gated ion channels and facilitated diffusion?

    <p>Gated ion channels are a type of facilitated diffusion</p> Signup and view all the answers

    What is the main function of the Na+/K+ pump?

    <p>To facilitate nerve transmission</p> Signup and view all the answers

    What type of transport is used by the Na+/K+ pump?

    <p>Primary active transport</p> Signup and view all the answers

    What is the role of the ATP hydrolysis in the Na+/K+ pump?

    <p>To phosphorylate the pump, causing a conformational change</p> Signup and view all the answers

    What is the purpose of the sodium-calcium exchanger?

    <p>To export calcium ions from muscle cells</p> Signup and view all the answers

    What is the role of the SGLUT in glucose absorption?

    <p>To facilitate the transport of glucose across the membrane</p> Signup and view all the answers

    What is the effect of digitoxin on the Na+/K+ pump?

    <p>It inhibits the pump by blocking the dephosphorylation step</p> Signup and view all the answers

    What is the role of CFTR in cells?

    <p>To facilitate the transport of chloride ions across the membrane</p> Signup and view all the answers

    What is the effect of cystic fibrosis on chloride transport?

    <p>It reduces chloride transport</p> Signup and view all the answers

    What is the purpose of oral rehydration therapy in cholera treatment?

    <p>To drive the uptake of sodium and water into cells</p> Signup and view all the answers

    What type of transport is used by the sodium-calcium exchanger?

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

    Study Notes

    Membrane Transport

    • Membranes are selectively permeable, blocking the passage of most hydrophilic molecules into cells and organelles.
    • Small uncharged or hydrophobic molecules can freely cross the membrane by simple diffusion along their concentration gradients.
    • Charged polar molecules require specialist proteins (pumps, transporters, pores) to cross the membrane.

    Mechanisms of Transport

    • Simple Passive Transport / Diffusion: solutes move down a concentration gradient crossing the membrane, and the rate of diffusion depends on the partition coefficient of the solute.
    • Facilitated Diffusion: solutes move down a concentration gradient crossing the membrane, requiring a membrane protein (ion channel); examples include Cl-/HCO3- channel in erythrocytes, aquaporin (water channel), and GLUT glucose transporters.
    • Gated Ion Channels: ion channels that allow facilitated diffusion, selective for different ions (K+, Na+, Ca2+), open or close in response to a stimulus (e.g., ligand-gated or voltage-gated).
    • (Primary) Active Transport: solutes move against a concentration gradient, requiring a membrane protein and energy from ATP hydrolysis; example: Na+/K+ pump (Na+/K+ ATPase) in the plasma membrane.
    • Secondary Active Transport: pre-established gradient is used to drive transport of solutes against a gradient, with ATP hydrolysis used to establish the primary gradient; examples include Na+/glucose cotransporter (SGLUT) and Na+/Ca2+ cotransporter.

    Na+/K+ Pump

    • Na+/K+ pump (Na+/K+ ATPase) is a primary active transport mechanism that uses energy from ATP hydrolysis to maintain a [Na+] and [K+] gradient across the plasma membrane.
    • The pump consists of a tetramer (α2β2) and uses ATP hydrolysis to phosphorylate the pump, causing a conformational change that drives the transport of Na+ and K+.

    GLUT Family

    • The GLUT family of glucose transporters (GLUT1-4) are involved in facilitated diffusion of glucose into cells.
    • Each GLUT has a specific location, function, and affinity for glucose, with GLUT4 being regulated by insulin to increase glucose uptake in muscle and adipose tissue.

    Clinical Considerations

    • Digitoxin: cardiac glycosides (digitoxin and digoxin) inhibit the Na+/K+ pump, leading to an increase in [Na+] and a loss of the Na+ gradient, resulting in increased [Ca2+] and contraction in heart muscle.
    • Ouabain: cardiac glycosides (ouabain) inhibit the Na+/K+ pump by blocking the binding of K+, also leading to increased [Na+] and [Ca2+] in heart muscle.
    • CFTR: cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-gated ion channel that regulates the movement of chloride ions, which in turn regulates water movement; mutations in CFTR cause cystic fibrosis.
    • Cholera Treatment: oral rehydration therapy includes high glucose concentration (~110 mM) which drives Na+ (and consequently Cl- and H2O) uptake into cells via SGLUT, treating cholera caused by Vibrio cholerae.

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    Description

    This quiz covers the fundamentals of membrane transport, including passive diffusion, facilitated transport, and active transport, as well as the structure and function of the Na+/K+-ATPase membrane pump.

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