Cell Signaling Pathways Overview
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Questions and Answers

What is the role of calcium in cellular processes?

  • Calcium acts as a secondary messenger in signaling. (correct)
  • Calcium levels are irrelevant to regulated secretion.
  • Calcium solely triggers muscle contraction.
  • Calcium is only involved in egg activation.

    • Which mechanism primarily initiates calcium waves during fertilization?

  • Calcium release from the endoplasmic reticulum.
  • Calcium entry via sperm entry triggering a calcium wave. (correct)
  • Calcium entry through ion channels.
  • Activation of GPCRs.

    • What is required for the function of IP3 receptors in calcium wave propagation?

  • Only Ca2+ is needed.
  • Both IP3 and ATP are required.
  • Both IP3 and Ca2+ are required. (correct)
  • Only IP3 is needed.

    • How do GPCRs contribute to the amplification of signals?

    <p>By initiating cascades that enhance signaling. (A)</p> Signup and view all the answers

    What type of signaling is utilized by rhodopsins in rod photoreceptors?

    <p>Light-sensitive GPCR signaling. (C)</p> Signup and view all the answers

    What effect do excitatory neurotransmitters have on the postsynaptic membrane?

    <p>They cause an influx of Na+ ions, leading to depolarization. (A)</p> Signup and view all the answers

    Which of the following statements about transmitter-gated channels is correct?

    <p>They can have different ion selectivity and binding sites. (C)</p> Signup and view all the answers

    What is the primary effect of inhibitory neurotransmitters on the postsynaptic membrane?

    <p>They can increase the threshold for firing an action potential. (A)</p> Signup and view all the answers

    Transmitter-gated channels are primarily characterized by which feature?

    <p>They possess highly selective binding sites for neurotransmitters. (B)</p> Signup and view all the answers

    What is the role of light-gated ion channels like channelrhodopsins?

    <p>They enable neurons to respond to light stimuli. (B)</p> Signup and view all the answers

    What is the primary reason for the differences in solute concentrations across the plasma membrane?

    <p>The lipid bilayer forms a barrier to polar molecules. (A)</p> Signup and view all the answers

    Which statement correctly describes passive transport?

    <p>It involves the movement from high to low concentration without energy. (A)</p> Signup and view all the answers

    Which type of molecules can cross the lipid bilayer rapidly?

    <p>Non-polar molecules. (D)</p> Signup and view all the answers

    What is required for active transport to occur?

    <p>An additional energy source. (C)</p> Signup and view all the answers

    What distinguishes channel proteins from transporters in membrane transport?

    <p>Channel proteins allow passive movement of small molecules. (B)</p> Signup and view all the answers

    Which of the following molecules would be least likely to cross the plasma membrane by passive diffusion?

    <p>Glucose. (A)</p> Signup and view all the answers

    In passive transport for charged molecules, which factors act as driving forces?

    <p>Both the concentration gradient and the membrane potential. (A)</p> Signup and view all the answers

    Which of the following correctly describes the electrochemical gradient?

    <p>It is the net driving force composed of concentration and membrane potential gradients. (B)</p> Signup and view all the answers

    What are the three types of protein filaments in the cytoskeleton?

    <p>Intermediate filaments, Microtubules, Actin filaments (A)</p> Signup and view all the answers

    Which junction forms a selective permeability barrier across epithelial cell sheets?

    <p>Tight junction (D)</p> Signup and view all the answers

    Which proteins are the main components of the sealing strands in tight junctions?

    <p>Claudins (C)</p> Signup and view all the answers

    What is the primary function of desmosomes?

    <p>Connect intermediate filaments of adjacent cells (C)</p> Signup and view all the answers

    What is the role of myosin in the actin network?

    <p>Facilitates the contraction of the actin network (C)</p> Signup and view all the answers

    Which type of anchoring junction forms a connection between cells and the extracellular matrix?

    <p>Hemidesmosome (C)</p> Signup and view all the answers

    What is the effect of occludin on tight junctions?

    <p>Influences the permeability of tight junctions (D)</p> Signup and view all the answers

    What type of intermediate filament is typically associated with desmosomes in heart muscle cells?

    <p>Desmin filaments (A)</p> Signup and view all the answers

    What is the main reason K+ channels are selective for K+ over Na+?

    <p>The interaction between K+ ions and the channel's amino acids displaces water molecules (B)</p> Signup and view all the answers

    Which statement describes the function of myelin sheath in neurons?

    <p>It insulates the axonal membrane to prevent ion leakage. (A)</p> Signup and view all the answers

    What contributes to the speed of nerve impulse propagation?

    <p>The jumping of action potentials between nodes of Ranvier (C)</p> Signup and view all the answers

    What is the role of voltage-gated channels in neurons?

    <p>They generate action potentials when depolarized (D)</p> Signup and view all the answers

    Which of the following represents the equilibrium potential determined by the Nernst equation?

    <p>The voltage at which there is no net movement of a specific ion across the membrane (C)</p> Signup and view all the answers

    How many subunits compose a voltage-gated Na+ channel?

    <p>Four subunits (C)</p> Signup and view all the answers

    What effect does myelination have on action potential propagation?

    <p>It increases the speed and efficiency of action potential propagation. (D)</p> Signup and view all the answers

    What is the primary function of K+ leak channels in the cell?

    <p>To allow passive flow of K+ towards resting potential (A)</p> Signup and view all the answers

    What chromophore is required for the function of light-gated ion channels?

    <p>all-trans-retinal (D)</p> Signup and view all the answers

    What is the significance of the ~0.6 nm pore size in light-gated ion channels?

    <p>It allows various cations to pass. (A)</p> Signup and view all the answers

    Which type of light do channelrhodopsins primarily respond to?

    <p>Blue light ~480 nm (B)</p> Signup and view all the answers

    Which process can be influenced by optogenetics in cell biology?

    <p>Cell migration (B)</p> Signup and view all the answers

    What is an important feature of the cytoskeleton?

    <p>It is a complex network of protein filaments. (B)</p> Signup and view all the answers

    What advantage do engineered photosensitive proteins provide in cellular optogenetics?

    <p>They allow for the precise control of cellular activities. (C)</p> Signup and view all the answers

    Which engineered light-sensitive domain can be used to control cell signaling?

    <p>PCB / Biliverdin (A)</p> Signup and view all the answers

    How quickly can channelrhodopsins return to their dark conformation after stimulation?

    <p>Within milliseconds (A)</p> Signup and view all the answers

    What distinguishes channel proteins from transporter proteins in terms of transport speed?

    <p>Transporter proteins can facilitate both passive and active transport. (D)</p> Signup and view all the answers

    Which statement accurately describes the function of the Na+-K+ pump?

    <p>It utilizes ATP to pump 3 Na+ out and 2 K+ into the cell. (B)</p> Signup and view all the answers

    What role does Ouabain play in the function of the Na+-K+ pump?

    <p>It acts as an inhibitor by competing with K+ for binding sites. (C)</p> Signup and view all the answers

    Which of the following best describes the action of ion channels in terms of concentration gradients?

    <p>They only allow passive transport of ions according to their gradients. (A)</p> Signup and view all the answers

    What mechanism does the Ca2+ ion pump use to maintain low intracellular calcium levels?

    <p>It uses ATP to actively transport Ca2+ out of the cell. (B)</p> Signup and view all the answers

    In the context of nerve cells, what differentiates various ion channels?

    <p>They exhibit different selectivities for specific ions. (C)</p> Signup and view all the answers

    What is a crucial function of aquaporins in cellular transport?

    <p>They facilitate the passive transport of water across membranes. (A)</p> Signup and view all the answers

    How does the Na+/glucose symporter function in the gut?

    <p>It is driven by the electrochemical Na+ gradient to import glucose. (C)</p> Signup and view all the answers

    Study Notes

    Cell Signaling Pathways

    • Cyclic-AMP (cAMP) activation through GPCRs: A signal molecule activates a G protein, leading to adenylyl cyclase activation. This enzyme converts ATP to cAMP. cAMP activates protein kinase A (PKA). PKA then phosphorylates CREB, which then binds to CRE, resulting in gene transcription.

    • PLC/PKC signaling: Phospholipase C (PLC) is activated, cleaving a membrane phospholipid into diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). DAG activates protein kinase C (PKC). IP3 releases calcium from the endoplasmic reticulum.

    • Calcium/Calmodulin controls downstream kinase activity: Calcium ions bind to calmodulin, altering its shape and enabling it to activate downstream kinases.

    • Calcium transients trigger many cellular processes: Calcium (Ca2+) release is triggered by various signals, not just GPCRs. This calcium release is involved in muscle contraction, neurotransmitter secretion, fertilization, and other cellular events.

    • PLC initiates calcium waves in egg activation: PLC plays a crucial role in initiating calcium waves during egg activation.

    • Calcium waves propagate through feedback: IP3 receptors require both IP3 and calcium (Ca2+) to initiate further calcium release events, creating a propagating wave throughout the cell.

    • How do signaling waves propagate across many cells?: This section explores how a signal affects surrounding cells.

    • Smell and Vision Dependent on GPCRs that Regulate Ion Channels: Smell and vision rely on specific GPCRs linked to ion channels, triggering responses to external stimuli.

    • Signals are amplified by cascades: A signal received from a receptor triggers a response. This response activates other downstream pathways and increases in proportion.

    • Rhodopsins – Light-sensitive GPCRs: Rhodopsin, a light-sensitive GPCR, triggers a cascade of downstream events in response to light, affecting the membrane potential.

    • There is cross-talk between many signaling pathways and types of receptors: Different signaling pathways can interact and influence each other, impacting the final outcome.

    • JAK-STAT signalling: Cytokine binding to receptors activates JAKs, which phosphorylate STAT proteins. Activated STAT proteins move to the nucleus to regulate gene expression.

    • Lab and closing remarks: The next section focuses on plant cell culture. The final exam will cover the material from this section and past material. The professor hopes students have enjoyed the course and asks them to take the evaluations seriously.

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    Description

    Explore the intricate mechanisms of cell signaling pathways, focusing on cyclic-AMP activation through GPCRs, PLC/PKC signaling, and the role of calcium and calmodulin in cellular processes. Understand how these pathways regulate critical functions like gene transcription and muscle contraction.

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