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What is the primary role of kinases in the signal transduction pathway described?

  • To add phosphates to proteins (correct)
  • To catalyze the breakdown of ATP
  • To activate receptor molecules directly
  • To remove phosphates from proteins
  • Which process is responsible for turning off the signal in a signaling cascade?

  • Dephosphorylation (correct)
  • Phosphorylation
  • Signal amplification
  • Transcriptional activation
  • In the context of signal transduction, what is the term for events that occur closer to the response rather than the receptor?

  • Receptor-mediated events
  • Cascading events
  • Downstream events (correct)
  • Upstream events
  • What is the effect of signal transduction pathways on the cellular response?

    <p>They can either enhance or diminish cellular activities.</p> Signup and view all the answers

    What is the specific role of phosphatases in the signaling pathways?

    <p>To remove phosphates and deactivate target proteins.</p> Signup and view all the answers

    What is a common feature of both G protein signaling pathways and the MAP-kinase pathway?

    <p>Both involve a series of phosphorylation events.</p> Signup and view all the answers

    Which type of protein actively regulates G protein activity, often modulating the effect of receptors?

    <p>G-protein–receptor kinases (GRKs)</p> Signup and view all the answers

    What is a characteristic of an inactive protein kinase in the signaling cascade?

    <p>It cannot catalyze the phosphorylation of substrates.</p> Signup and view all the answers

    What is the role of phosducin in G protein signaling pathways?

    <p>It modifies the βγ subunits of G proteins.</p> Signup and view all the answers

    How do receptors with inherent tyrosine kinase activity generally function?

    <p>They undergo autophosphorylation upon ligand binding.</p> Signup and view all the answers

    What is the specific role of the SH2 domain in the Ras-MAP kinase pathway?

    <p>It forms binding sites for proteins with phosphotyrosine residues.</p> Signup and view all the answers

    Which factors act as upstream regulators in the MAP kinase pathway?

    <p>Grb2 and SOS proteins.</p> Signup and view all the answers

    What is the significance of receptor autophosphorylation in signaling?

    <p>It creates binding sites for signal transducer proteins.</p> Signup and view all the answers

    Which of the following describes the relationship between Ras and Raf in the MAP kinase pathway?

    <p>Ras activates Raf through a conformational change.</p> Signup and view all the answers

    Which process is primarily modulated by G-protein-receptor kinases (GRKs)?

    <p>Receptor desensitization.</p> Signup and view all the answers

    What is the primary function of SOS in G protein signaling?

    <p>It functions as a GEF for Ras.</p> Signup and view all the answers

    What physiological effects arise from the generation of free βγ subunits in G protein signaling?

    <p>They can phosphorylate ligand-occupied receptors.</p> Signup and view all the answers

    How do βγ subunits influence the mitogen-activated protein kinase (MAP-kinase) pathway?

    <p>They activate the MAP-kinase pathway at an early step.</p> Signup and view all the answers

    What is the primary role of phosducin in G protein signaling?

    <p>To sequester βγ subunits and prevent their reassociation.</p> Signup and view all the answers

    What role does the GoLoco protein play in G protein signaling?

    <p>It releases free βγ dimers without activating receptors.</p> Signup and view all the answers

    What is one way that βγ subunits can regulate receptors?

    <p>By directing GRKs to phosphorylate ligand-occupied receptors.</p> Signup and view all the answers

    Which cellular process is influenced by the βγ subunit complex due to its membrane tethering?

    <p>Membrane trafficking processes.</p> Signup and view all the answers

    Which statement correctly describes the action of free βγ subunits in G protein signaling?

    <p>They can activate several effector proteins in addition to influencing the MAP-kinase pathway.</p> Signup and view all the answers

    What effect does the sequestration of βγ subunits by phosducin have on G protein activity?

    <p>It eventually inhibits G protein activity by curtailing βγ activity.</p> Signup and view all the answers

    Study Notes

    Cell Signaling Overview

    • Cell signaling, or cell-to-cell communication, is vital for multicellular organisms.
    • Intercellular signaling mechanisms allow one cell to send a message changing another cell's function.
    • Cell communication occurs in multiple ways.

    Types of Cell Signaling

    • Juxtacrine/Contact-Dependent: Direct contact between cells, via gap junctions or cell surface proteins.
    • Intercellular Signaling (Contact-Independent): Signaling molecules secreted by one cell and received by others. This includes several forms:
      • Endocrine: Hormones travel long distances via blood, affecting target cells at distant locations.
      • Paracrine: Secreted molecules affect nearby target cells locally, without the involvement of the bloodstream.
      • Synaptic/Neuronal: Nerve cells release neurotransmitters to target cells.
      • Autocrine: A cell secretes signaling molecules that bind to receptors on itself (direct feedback loop).

    Intracellular Signal Transduction

    • Key components of a signal cascade, such as:

      • Receptors
      • Signal transduction, includes a sequence of reactions that mediate the response to a signal.
      • Response.
    • Signals relay in multistep pathways, amplifying the initial signal.

    Signal Termination

    • Termination of signals within the cell.
      • The first process is messenger degradation/removal.
      • Specific steps within signal transduction pathways include receptor desensitization or inactivation of the second messenger.
      • Processes that terminate signals are carefully controlled.

    Chemical Messengers

    • Chemical messengers that act as signals include:
      • Neurotransmitters released in the nervous system.
      • Hormones released by glands and transported in the circulatory system.

    Types of Receptors

    • Intracellular receptors: Bind to small, hydrophobic molecules (e.g., steroid hormones). These messengers readily diffuse across plasma membrane.
    • Plasma membrane receptors: Bind to large, hydrophilic molecules, unable to cross membrane. These include:
      • Ion channel receptors
      • Receptors that are enzymes (kinases) or that bind and activate enzymes.
      • G-protein-coupled receptors

    G-Protein Coupled Receptors (GPCRs)

    • Contain 7 transmembrane (7TM) domains (alpha-helices).
    • Ligand binding alters receptor conformation, leading to G protein activation.
    • G protein activation subsequently influences effector proteins (e.g., enzymes, ion channels).
    • The G protein cycle typically involves GTP binding and hydrolysis. The hydrolysis returns the G protein back to its inactive state.
    • G proteins are divided into families, each with specific functions (e.g., Gs, Gi, Gq).

    Small G Proteins

    • Small GTPases, associated with cellular functions like membrane trafficking, gene activation, and cell growth.
    • Examples include Ras, Rho, Rac, etc.
    • Small G proteins control processes, especially by activating a cascade of kinases.

    Receptors that are Kinases

    • Receptors with internal tyrosine kinase activity.
    • Receptors that recruit intracellular tyrosine kinases.
    • Involved in signal transduction pathways.
    • Example pathways include the Ras-MAP kinase pathway.
    • These pathways work through signal protein assemblies, which have three dimensional shapes (e.g., SH2 and SH3 domains).

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