Cell Biology: Membrane Transport and Ion Channels
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Questions and Answers

Which of the following best describes the role of Ca2+ ions in cellular processes?

  • Responsible for maintaining a negative resting membrane potential.
  • Catalyzing the breakdown of large molecules into smaller units.
  • Primary structural components of the cell membrane.
  • Involved in various signaling pathways, including neuronal communication and muscle contraction. (correct)

    • What happens to the membrane potential when Ca2+ ions enter the cell?

  • The membrane potential becomes more negative, resulting in hyperpolarization.
  • There is no change in membrane potential during calcium ion influx.
  • The membrane potential becomes less negative, tending towards depolarization. (correct)
  • The membrane potential gets closer to zero, causing isoelectric point.

    • What is the defining characteristic of excitable cells?

  • They possess gated ion channels that respond to specific stimuli, allowing rapid changes in membrane potential. (correct)
  • They are incapable of experiencing depolarization or hyperpolarization.
  • They have a fixed membrane potential.
  • They lack gated ion channels.

    • Which of the following stimuli can cause voltage-gated ion channels to open?

    <p>Changes in membrane potential. (D)</p> Signup and view all the answers

    What is the immediate effect of changes in membrane potential on a neuron?

    <p>Rapid ion fluxes that can cause either depolarization or hyperpolarization. (A)</p> Signup and view all the answers

    What is the primary role of leak channels in a cell membrane?

    <p>To establish and maintain the resting membrane potential. (B)</p> Signup and view all the answers

    Which type of ion channel opens in response to changes in the electrical potential across the cell membrane?

    <p>Voltage-gated ion channel (D)</p> Signup and view all the answers

    If a cell's membrane potential is at -70 mV, and it is permeable only to potassium, what is the most likely outcome?

    <p>Potassium ions will flow out of the cell, further decreasing the membrane potential. (D)</p> Signup and view all the answers

    What effect does the movement of potassium ions out of the cell have on the cell's membrane potential?

    <p>It makes the membrane potential more negative. (A)</p> Signup and view all the answers

    Which of the following is true regarding the concentration and electrical gradients of potassium (K+)?

    <p>The concentration gradient favors potassium leaving the cell, and the electrical gradient favors potassium entering the cell. (B)</p> Signup and view all the answers

    What is the equilibrium potential for potassium (K+) at which the electrical and concentration gradients are balanced?

    <p>Approximately -90 mV (B)</p> Signup and view all the answers

    Why is the resting membrane potential of a typical animal cell approximately -70 mV, considering the equilibrium potential for K+ is -90 mV?

    <p>Because the cell also has some permeability to other ions, such as sodium. (D)</p> Signup and view all the answers

    How does the concentration of sodium (Na+) differ between the inside and outside of a typical cell, and what is its effect?

    <p>Na+ is more concentrated outside the cell, and it will move in if given the chance, tending to make the membrane potential more positive. (D)</p> Signup and view all the answers

    What is the most likely outcome if a cell membrane suddenly becomes more permeable to sodium (Na+)?

    <p>The membrane potential will become more positive, depolarizing the cell towards the equilibrium of Na+. (A)</p> Signup and view all the answers

    Which of the following is NOT a typical category of ion channels?

    <p>ATP-gated ion channels (A)</p> Signup and view all the answers

    Flashcards

    Ion Channels

    Transmembrane proteins that form pores in the plasma membrane, allowing selective passage of specific ions.

    Non-gated Ion Channels

    Ion channels that are always open, allowing a continuous flow of specific ions across the membrane.

    Membrane Potential

    The difference in electrical charge across a cell membrane, measured in millivolts (mV).

    Resting Membrane Potential

    The membrane potential of a cell at rest, when it is not actively receiving any signals.

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    Leak Channels

    Non-gated ion channels that are mainly responsible for establishing the resting membrane potential.

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    Electrochemical Gradient

    The tendency of an ion to move across a membrane due to differences in concentration and electrical charge.

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    Electrochemical Equilibrium

    The movement of ions across a membrane reaches an equilibrium where the electrical gradient is equal and opposite to the concentration gradient.

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    Ligand-Gated Ion Channel

    A type of ion channel that opens or closes in response to a specific chemical stimulus.

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    Mechanosensitive Ion Channel

    A type of ion channel that opens or closes in response to a mechanical force.

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    Voltage-Gated Ion Channel

    A type of ion channel that opens or closes in response to changes in the membrane potential.

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    What are Ca2+ ions?

    Calcium ions are important signaling molecules that are used in various cellular processes.

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    Where is Ca2+ more concentrated?

    Calcium ions are more concentrated outside the cell than inside due to active transport mechanisms.

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    What are excitable cells?

    Excitable cells are specialized cells that can change their membrane potential in response to stimuli.

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    What are voltage-gated ion channels?

    Voltage-gated ion channels open or close in response to changes in membrane potential.

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    What is depolarization and hyperpolarization?

    Depolarization makes the membrane potential more positive, while hyperpolarization makes it more negative.

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    Study Notes

    Membrane Transport

    • Membrane transport involves the movement of substances across cell membranes
    • Ions move through channels, which are pores in the plasma membrane
    • Ion channels are selective, allowing specific ions to pass
    • These channels are categorized into:
    • Non-gated channels
    • Ligand-gated channels
    • Mechanosensitive channels
    • Voltage-gated channels

    Ion Channels

    • Ion channels are transmembrane proteins that form pores in the plasma membrane.
    • These pores allow select ions to pass through the membrane.
    • Ion channels are present in all eukaryotic cells.
    • Over 100 different ion channels have been identified.
    • Ion channels are typically selective for one specific ion (e.g., K+, Na+, Ca2+), or group of ions.
    • Channels can open and close in response to stimuli.

    ATP-Powered Pumps

    • Ion channels often open or close based on specific instructive signals.
    • Examples of ATP-powered pumps are involved in active transport.

    Ion Distribution

    • Ion concentration varies inside and outside the cell.
    • Key ion channels help maintain these concentration gradients
      • Channels are important for controlling flow of specific ions into and out of the cell.

    Ion Channels & Membrane Potential

    • All eukaryotic cells contain ion channels.
    • Leak channels are important for resting membrane potential. Leak channels allow potassium (K+) to freely cross the membrane, making the inside of the cell more negatively charged compared to the outside.
    • By controlling the flow of ions, the membrane maintains its potential
    • The resting membrane potential is typically -70 mV in animal cells.

    K+ (Potassium) Ions

    • K+ ions move out of the cell, down their concentration gradient.
    • This creates a negative membrane potential (-90mV).
    • For the K+ to leave the cell, the electrical gradient and the concentration gradient of the ions need to balance.
    • The movement of K+ across the channels reaches equilibrium when the concentration gradient and the electrical gradient are balanced.
    • Equilibrium is reached at -90 mV.

    Na+ (Sodium) Ions

    • Na+ ions tend to be more concentrated outside the cell.
    • When allowed to enter the cell, Na+ will move down its concentration gradient.
    • This leads to a more positive membrane potential (+60 mV).
    • This movement of sodium is critical for how excitable cells function.

    Ca2+ (Calcium) Ions

    • Ca2+ ions are also important signalling molecules.
    • Ca2+ is more concentrated outside the cell compared to inside.
    • When allowed to move into the cell, it moves down its concentration gradient.
    • This results in a more positive membrane potential.

    Excitable Cells

    • Excitable cells, including neurons and muscle cells, possess gated ion channels.
    • These channels respond to specific stimuli such as changes in voltage, mechanical stimuli, and the presence of extracellular or intracellular signaling molecules (ligands).
    • Changes in membrane potential because of ion fluxes are important in excitable cells.
    • Depolarization (more positive potential) and hyperpolarization (more negative potential) occur rapidly in response to ion fluxes.

    Voltage-gated Ion Channels

    • These channels are sensitive to changes in membrane potential.
    • A voltage sensor in the channel changes its conformation to allow ions to pass through based on alterations of charge in the membrane.

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    Description

    Explore the mechanisms of membrane transport, including the movement of ions across cell membranes through various types of ion channels. Learn about the characteristics and functions of non-gated, ligand-gated, mechanosensitive, and voltage-gated channels, along with the role of ATP-powered pumps in active transport.

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