Biochem 3.3 Biology Chapter: Ion Channels and Membrane Function
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Questions and Answers

Why can't Na+ ions pass through a potassium channel pore?

  • Na+ ions are larger than K+ ions.
  • Na+ ions have a different charge than K+ ions.
  • Desolvated Na+ ions are too small to form interactions. (correct)
  • Na+ ions cannot desolvate properly.

    • What drives the net flow of uncharged solutes through a channel?

  • The size of the solute particles.
  • Temperature of the surrounding environment.
  • The ionic charge of solutes.
  • Concentration gradient across the membrane. (correct)

    • What happens to the charges on either side of a membrane when potassium ions flow out?

  • Positive charges accumulate outside the membrane. (correct)
  • Negative charges build up outside the membrane.
  • Positive charges increase inside the vesicle.
  • The charges on both sides remain neutral.

    • What occurs when the positive charges outside the membrane resist additional potassium flow?

    <p>Potassium ions will be driven back inside the membrane.</p> Signup and view all the answers

    What stabilizes potassium ions within the potassium channel?

    <p>Residues of the channel protein.</p> Signup and view all the answers

    What happens to potassium concentrations across the membrane over time?

    <p>The concentrations become equal on both sides.</p> Signup and view all the answers

    What role do channels primarily play for charged particles like potassium?

    <p>Channels mediate the flow of ions across the membrane.</p> Signup and view all the answers

    What occurs during the process of repolarization in a cell?

    <p>Potassium flows out of the cell, decreasing the membrane potential.</p> Signup and view all the answers

    How do mechanically gated ion channels operate?

    <p>They open in response to physical stimuli.</p> Signup and view all the answers

    What characterizes carrier proteins compared to channel proteins?

    <p>Carrier proteins can move solutes against their electrochemical gradient.</p> Signup and view all the answers

    What is the role of aquaporins in a cell's membrane?

    <p>They allow the passage of uncharged particles.</p> Signup and view all the answers

    What happens to the membrane potential when cells with channels A and B are exposed to a neutral molecule?

    <p>The membrane potential increases then decreases.</p> Signup and view all the answers

    What does the flow of ions through a channel create across a cell membrane?

    <p>Charge buildup</p> Signup and view all the answers

    Which equation describes the relationship between ion concentration and membrane potential?

    <p>Nernst equation</p> Signup and view all the answers

    If the intracellular concentration of a positive ion is greater than its extracellular concentration, what is the sign of the equilibrium potential?

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

    What happens to the membrane potential when there is increased intracellular anion concentration?

    <p>It becomes positive</p> Signup and view all the answers

    What elements does the simplified form of the Nernst equation involve at physiological temperature?

    <p>R, T, and F</p> Signup and view all the answers

    Which ion is represented as having a negative charge in the context of membrane potential?

    <p>Chloride (Cl−)</p> Signup and view all the answers

    What term describes an ion that cannot cross the membrane?

    <p>Nonpermeable ion</p> Signup and view all the answers

    What happens to membrane potential when the permeability of sodium (Na+) increases significantly?

    <p>Membrane potential becomes less negative or more positive.</p> Signup and view all the answers

    What is the value for Faraday's constant used in calculations related to equilibrium potential?

    <p>96,500 C/mol</p> Signup and view all the answers

    Which factor does NOT influence the actual membrane potential in a cell?

    <p>Volume of the cell</p> Signup and view all the answers

    In the equation for determining membrane potential, how is the chloride ion ratio structured?

    <p>In:Out ratio</p> Signup and view all the answers

    What type of channels are always open, allowing specific ions to flow continuously?

    <p>Ungated ion channels</p> Signup and view all the answers

    Given a vesicle with 100 mM sodium inside and a 10 mM sodium solution outside, what is the goal of the equilibrium potential?

    <p>To prevent sodium ions from diffusing out</p> Signup and view all the answers

    What is the primary condition for the majority of ion channels before a signal is received?

    <p>They remain closed.</p> Signup and view all the answers

    How does the initial concentration of Na+ compare inside and outside of a cell at rest?

    <p>Extracellular Na+ concentration is greater.</p> Signup and view all the answers

    What effect does an increase in potassium (K+) permeability typically have on the membrane potential?

    <p>Membrane potential becomes more negative.</p> Signup and view all the answers

    In determining membrane potential, which of the following ions is primarily considered along with sodium and potassium?

    <p>Chloride (Cl−)</p> Signup and view all the answers

    When a channel opens upon signal receipt, what change occurs in the ions?

    <p>Ions flow until the gate closes again.</p> Signup and view all the answers

    What characteristic is primarily responsible for ungated potassium channels not equalizing potassium concentrations on both sides of the membrane?

    <p>Active pumping of potassium into the cytosol</p> Signup and view all the answers

    What is the primary action of ligand-gated ion channels when a ligand binds?

    <p>They open the gate to allow ion flow.</p> Signup and view all the answers

    What occurs when acetylcholine binds to ligand-gated channels on muscle cells?

    <p>Sodium ions enter the cell, causing depolarization.</p> Signup and view all the answers

    Which of the following describes what happens during desensitization of ligand-gated ion channels?

    <p>The channels close even with continued ligand presence.</p> Signup and view all the answers

    How do voltage-gated ion channels respond to changes in membrane potential?

    <p>They have a threshold that triggers opening at specific potentials.</p> Signup and view all the answers

    What effect does the opening of voltage-gated sodium channels have after ligand-gated sodium channels are activated?

    <p>It further depolarizes the membrane potential.</p> Signup and view all the answers

    What kind of ion flow do intracellular organelle ungated channels typically allow?

    <p>Ions to flow between the cytosol and the organelle lumen.</p> Signup and view all the answers

    What triggers the inactivation of voltage-gated sodium channels?

    <p>Strong membrane depolarization.</p> Signup and view all the answers

    What is the general role of potassium channels in maintaining membrane potential?

    <p>They help to maintain a resting membrane potential.</p> Signup and view all the answers

    Which statement best describes the function of ligand-gated channels in muscle contraction?

    <p>They increase sodium influx which leads to depolarization and contraction.</p> Signup and view all the answers

    Study Notes

    Potassium Channel Function

    • Potassium channels selectively allow potassium ions (K+) through, but not sodium ions (Na+), due to specific interactions and size differences
    • Potassium ions dissociate from surrounding water molecules and bind to residues within the pore, while sodium ions are too large or small for stabilization
    • Solutes can move through channels in either direction
    • Direction of movement is influenced by concentration gradients; solutes move from higher to lower concentration for uncharged solutes
    • Channels mediate ion movement, considering charge effects
    • Example: Potassium chloride (KCl) vesicle - potassium flows from higher to lower concentration, creating a charge imbalance

    Channel Regulation and Flow

    • Channels facilitate ion passage, and charge imbalances must be considered
    • Channels mediate flow down concentration gradients
    • Initially, both sides of a membrane have a net charge of 0 (e.g., potassium chloride)
    • As potassium flows outward, positive charges build on the outside
    • Simultaneously, negative charges build inside, resisting further potassium flow
    • Eventually, flow rates equalize, even with different concentrations on each side
    • Charge separation creates a counteracting force influencing ion flow based on both concentration and charge
    • Membrane potential is a result of charge separation across a membrane
    • Nernst equation describes equilibrium potential, considering ion concentration and charge

    Ion Channels and Membrane Potential

    • Equilibrium potential (E) calculated using the Nernst equation (E = RTzF/ [Xin]/[Xout]), considering the gas constant (R), temperature (T), charge (z), Faraday's constant (F), and intracellular/extracellular ion concentrations
    • Negative equilibrium potential for positive ions with higher intracellular concentration than extracellular concentration.
    • Increased intracellular concentration of a positive ion results in a negative equilibrium potential
    • Equilibrium potential is the membrane voltage required to balance the concentration gradient driving ion movement
    • Imbalance in concentrations causes a voltage difference

    Types of Ion Channels

    • Ungated channels allow continuous ion flow
    • Potassium channels are often ungated
    • Ligand-gated channels open in response to a ligand binding to the channel protein.
    • Voltage-gated channels open in response to changes in the membrane potential.
    • Mechanically-gated channels open in response to physical forces.

    Carrier Protein Function

    • Carrier proteins transfer solutes across cell membranes, unlike channels that allow continuous flow
    • Movement may be in one direction (uniport), or both directions can be involved in their movement (symport or antiport)
    • These proteins can facilitate transport down or against a gradient by utilizing energy (e.g., ATP hydrolysis).
    • Carry polar molecules
    • Example: Aquaporins are carrier proteins that transport water
    • Example: GLUT2 (glucose transporter) moves glucose into cells

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    Description

    This quiz explores key concepts regarding ion channels, particularly focusing on potassium and sodium ions. Learn about the mechanisms of ion flow, the role of channels in repolarization, and the impact of solute movement on membrane potential. Delve into the specifics of channel and carrier protein functions for a deeper understanding of cellular processes.

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