WSC331 Bioelectricity and Biophotonics Engineering Quiz
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Questions and Answers

What does the Nernst potential represent in bioelectricity?

  • The rate of ion diffusion across the membrane
  • The average concentration of ions in the cytoplasm
  • The total current through the membrane
  • The transmembrane potential for a single ion at equilibrium (correct)

    • What is the primary characteristic of resting potential?

  • It occurs only during nerve impulse transmission.
  • It is the weighted average of Nernst potentials of all ions. (correct)
  • It does not vary depending on ion concentrations.
  • It is equal to the total current flowing across the membrane.

    • What does Donnan equilibrium describe?

  • The equilibrium of individual permeable ions in a solution (correct)
  • The average value of Nernst potentials across various cell types
  • The total balance of positive and negative charges in a membrane
  • The inability of all ions to reach equilibrium simultaneously

    • Which statement correctly defines quasineutrality?

    <p>Anions and cations in a solution should be approximately equal in concentration.</p> Signup and view all the answers

    What role does the transmembrane potential play in a cell's biology?

    <p>It operates as a voltage that drives cell signaling and membrane transport.</p> Signup and view all the answers

    What is the primary function of gating in voltage-sensitive elements?

    <p>To mediate conformational changes</p> Signup and view all the answers

    How can channel conductance be assessed?

    <p>By measuring ion currents at varying transmembrane potentials</p> Signup and view all the answers

    What does an ideal voltage clamp setup require?

    <p>A DC power supply and ammeter</p> Signup and view all the answers

    What happens to the measured transmembrane voltage (Vm) due to resistance in a realistic setup?

    <p>Vm is significantly lower than VDC</p> Signup and view all the answers

    What components contribute to the ionic currents in the voltage clamp equation?

    <p>The total of all ionic currents</p> Signup and view all the answers

    What does the variable 'g' represent in the context of channel conductance?

    <p>The conductance for specific ions</p> Signup and view all the answers

    In the voltage clamp technique, what does 'Cm' refer to?

    <p>The capacitance per unit area of the membrane</p> Signup and view all the answers

    What is a key insight gained from using the voltage clamp technique?

    <p>Gaining insights into channel conductivity</p> Signup and view all the answers

    What is the primary function of ion channels?

    <p>To allow the flow of ions through a pore</p> Signup and view all the answers

    Which technique is primarily used to measure the conductance of ion channels?

    <p>Patch clamp</p> Signup and view all the answers

    What significant milestone in the field of ion channels occurred in 1982?

    <p>Determination of a protein channel's structure</p> Signup and view all the answers

    What does the transmembrane potential (Vm) represent?

    <p>The difference in electrical charge across the cell membrane</p> Signup and view all the answers

    Which property of ion channels allows them to selectively permit certain ions?

    <p>Pore size and shape</p> Signup and view all the answers

    What structural feature do ion channels typically have?

    <p>Several subunits that form a water-filled pore</p> Signup and view all the answers

    In which time period did the concept of ion channels first emerge?

    <p>1950s</p> Signup and view all the answers

    What is one challenge in studying the structure of ion channels?

    <p>The difficulty of crystallizing integral membrane proteins</p> Signup and view all the answers

    Study Notes

    WSC331 Bioelectricity and Biophotonics Engineering

    Recap of previous lecture

    • Intracellular medium: Contains Anions(A-), Potassium(K+), and Chloride(Cl-) ions.
    • Extracellular medium: Contains Sodium(Na+) and Chloride(Cl-) ions.
    • Interior/Cytoplasm: Diagram illustrating ion movement across the membrane.
    • Extracellular medium: Similar diagram illustrating ion movement across the membrane, but on the outside of the cell.

    Concepts

    • Nernst Potential: Equilibrium transmembrane potential for a single ion. Formula provided.
    • Resting Potential: Equilibrium transmembrane potential. Weighted average of Nernst potentials.
    • Donnan equilibrium: All permeable ions are individually in equilibrium. Formula showing equilibrium concentration relationship.
    • Quasineutrality: Concentrations of anions and cations in a solution are equal.

    Today's lecture

    • Ion Channels: Focus on structure, and biophysical methods such as voltage clamp and patch clamp for measuring conductance and channel gating.

    Ion Channels - Historical Perspective

    • 1950: Concept of ion channels emerged.
    • 1976: Observation of behavior of individual channels.
    • 1982: Determination of the structure of the first protein channel.
    • 200x: Thousands of scientific papers per year are dedicated to ion channels.

    The cell membrane

    • Phospholipid bilayer. Proteins, channels, pumps, and ion channels are embedded.
    • Ion channels are selective and gated.

    Ion Channels: Structure

    • Ion channels are pore-forming proteins that allow ion flow.
    • Size larger than the membrane.
    • Non-polar parts are embedded in the membrane.
    • Variable cross-section.
    • Selectivity is not simply steric, but based on size and charge.
    • Some parts contain dipoles.
    • Voltage-sensitive elements are involved in gating.

    Ion Channels: Structure - Genetics

    • Gene cloning methods are crucial for investigating channels.
    • Primary structure is known, but secondary and tertiary structures are still not completely understood.
    • Runs of hydrophobic amino acids extend across the membrane.

    Classification of Ion Channels

    • Global view of 143 members of structurally related ion channel genes.
    • Seven groups of ion channel families.
    • Membrane topologies are highlighted.

    Ion Channels: Structure

    • Size is greater than the membrane.
    • Nonpolar parts are embedded in the membrane.
    • Variable cross section.
    • Selectivity is not just steric, also depends on charge.
    • Dipoles are present in some parts.
    • Elements responsible for gating are voltage-sensitive.

    Channel Conductance

    • How channel conductance is determined.
    • Details about the circuit and the formula relating current to channel conductance.

    Voltage Clamp

    • Technique for measuring ion currents while maintaining constant transmembrane potential.
    • Provides insights into channel conductivity.
    • Idealized situation: A DC power supply and an ammeter are required.
    • Real-world scenario: The resistance is not zero, and a feedback loop is needed.

    Voltage Clamp (I)

    • Measuring membrane voltage (Vm) with an amplifier using an internal recording electrode inserted into the cell and an external reference electrode.

    Voltage Clamp (II)

    • Setting the desired membrane voltage (Vc) using a command voltage.
    • Generating voltage clamp signal based on the difference between Vm and Vc

    Voltage Clamp (III)

    • Amplifier generates a current signal based on the difference between required Vm and Vc.
    • Injecting current to get Vm=Vc

    Voltage Clamp (IV)

    • Measuring current required to match Vm=Vc.
    • Measuring current flux across ion voltage-gated channels.

    Voltage Clamp: Current trace

    • Showing the difference between actual and commanded voltage.
    • Depicting a current trace and the different phases involved in voltage clamp.

    Patch Clamp

    • Special technique. It separates ion channel behaviour from other membranes.
    • Looks at one channel's behaviour.
    • Monitors current passing through individual membrane channels.
    • Challenge: Observing very small current flow.

    Patch Clamp: Current Traces

    • Patch-clamp records show discontinuities reflecting channel opening and closing.
    • Channels have open and closed states.
    • Channel opening and closing times vary randomly.

    Single-channel conductance

    • Conductance may depend on the current value.

    Single-channel conductance

    • Macroscopic conductance (conductance of all channels): Product of channel conductance and the number of channels.
    • This is exemplified by various ion channels in cells from different animals.

    Channel Gating

    • Activation/Inactivation.
    • Conformational changes due to changes in transmembrane potential.
    • Forces applied to the charged particles embedded in the membrane.
    • Ligand binding.
    • Inactivation "visualisations": (subject to guessing).

    Today's lecture (summary)

    • Ion channels structure
    • Biophysical methods (voltage clamp, patch clamp)
    • Conductance measurements
    • Channel gating

    Next lecture

    • Ion channels
    • Link between microscopic and macroscopic quantities
    • Macroscopic model: Dynamics of a first-order system
    • Hodgkin-Huxley model (K and Na channels)

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    Related Documents

    Bioelectricity and Biophotonics Engineering Past Lecture Notes PDF

    Description

    Test your knowledge on the key concepts of Bioelectricity and Biophotonics Engineering covered in WSC331. This quiz focuses on intracellular and extracellular mediums, as well as important potentials like Nernst and resting potential. Dive into the intricacies of ion movements and equilibrium to solidify your understanding.

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