Biology: Intracellular Signalling Pathways
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Questions and Answers

What is the primary function of the transduction stage in signal transduction?

  • Recognition of signaling molecules by receptors
  • Binding of ligands to receptors
  • Generation of secondary messengers (correct)
  • Regulation of cellular activities

    • What type of receptor recognizes signaling molecules in the cytosol?

  • GPCR (G protein-coupled receptor)
  • Ligand receptor
  • Intracellular receptor (correct)
  • Membrane receptor

    • What is the outcome of an agonist binding to a receptor?

  • Activation of intracellular signal transduction events (correct)
  • Binding of ligands to G proteins
  • Inhibition of intracellular signal transduction events
  • Regulation of cellular activities without signal transduction

    • What is the role of G proteins in G protein-coupled receptor signaling?

    <p>Activation of effector proteins</p> Signup and view all the answers

    What is the final stage of signal transduction?

    <p>Regulation of cellular activities</p> Signup and view all the answers

    What is the term for the binding of a signaling molecule to its receptor?

    <p>Ligand binding</p> Signup and view all the answers

    What is the primary function of parathyroid hormone in the body?

    <p>Regulating serum calcium concentration</p> Signup and view all the answers

    What is the significance of calcium in the body?

    <p>It is essential for skeletal mineralization and bone health</p> Signup and view all the answers

    What is the characteristic of hypocalcaemia?

    <p>Calcium levels are &lt; 8.5 mg/dL</p> Signup and view all the answers

    Where is the largest concentration of calcium found in cells?

    <p>Endoplasmic reticulum</p> Signup and view all the answers

    What is the function of PMCA in cells?

    <p>To maintain low cytosolic calcium levels</p> Signup and view all the answers

    How do calcium sinks work in cells?

    <p>Calcium flows from the extracellular matrix to the cytosol and then to the smooth endoplasmic reticulum</p> Signup and view all the answers

    What is the significance of calcium in skeletal mineralization?

    <p>It is essential for bone growth and development</p> Signup and view all the answers

    What percentage of calcium in the body is found in the bones of the skeleton?

    <p>&gt; 99%</p> Signup and view all the answers

    What is the function of an antagonist in a GPCR signalling pathway?

    <p>It binds to the receptor but does not activate it, blocking the effects of agonists</p> Signup and view all the answers

    What is the structure of the receptor part of GPCRs?

    <p>A membrane receptor with 7 transmembrane regions and extracellular and cytosolic regions</p> Signup and view all the answers

    What is the function of Gα in GPCR signalling pathways?

    <p>It carries the binding site for GDP and GTP</p> Signup and view all the answers

    What is the outcome of activation of a Gs active alpha subunit?

    <p>Activation of adenylyl cyclase and cAMP signalling pathway</p> Signup and view all the answers

    What is the function of adenyl cyclase in GPCR signalling pathways?

    <p>It converts ATP into cAMP</p> Signup and view all the answers

    What is the outcome of activation of a Gq active alpha subunit?

    <p>Activation of phospholipase C and IP3/DAG signalling pathway</p> Signup and view all the answers

    What is the function of signal amplification in GPCR signalling pathways?

    <p>It increases the signal received by the cell</p> Signup and view all the answers

    What is the outcome of activation of a Gi active alpha subunit?

    <p>Inhibition of adenylyl cyclase and cAMP signalling pathway</p> Signup and view all the answers

    What is the structure of G-proteins in GPCR signalling pathways?

    <p>Heterotrimeric proteins made up of alpha, beta, and gamma subunits</p> Signup and view all the answers

    What is the function of the beta-gamma subunit in GPCR signalling pathways?

    <p>It activates signal transduction pathways</p> Signup and view all the answers

    What is the primary function of NCX in the cell?

    <p>To maintain low cytosolic Ca2+ levels</p> Signup and view all the answers

    What is the energy requirement for SERCA to function?

    <p>ATP dependent</p> Signup and view all the answers

    Which of the following channels is opened by ligand binding?

    <p>Ligand-gated ion channels</p> Signup and view all the answers

    What is the number of binding sites for calcium in calmodulin?

    <p>4</p> Signup and view all the answers

    What is the primary mechanism of action of calcium channel blockers?

    <p>Blocking calcium influx</p> Signup and view all the answers

    Which of the following is NOT a mechanism that increases intracellular Ca2+?

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

    What is the primary effect of calcium channel blockers on blood vessels?

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

    What is the role of calmodulin in the cell?

    <p>To bind to calcium and activate other proteins</p> Signup and view all the answers

    Study Notes

    Signal Transduction Pathways

    • The 4 sections of signal transduction are:

      • Signals: ligand
      • Receptors: recognise signalling molecules, cause a conformation change
      • Transduction: signalling cascade with secondary messengers
      • Response: regulation of cellular activities

    • Signalling molecules are recognised by:

      • Membrane receptors (such as GPCRs)
      • Intracellular receptors

    G-Protein Coupled Receptors (GPCRs)

    • GPCRs are cell receptors linked to a G protein on the plasma membrane

    • GPCRs work in the plasma membrane by:

      • Ligand binds to receptor on plasma membrane
      • Activates G-protein
      • G-protein activates effector
      • Generates secondary messengers

    • Structure of GPCRs:

      • Membrane receptors (except rhodopsin)
      • Single α-helix polypeptide chain
      • 7-Transmembrane regions (H)
      • Extracellular (E) and cytosolic regions (C)

    Agonists and Antagonists

    • Agonists: bind to the receptor and activate it, leading to intracellular signal transduction events
    • Antagonists: bind to the receptor, but do not activate it, blocking the effects of agonists at the receptor

    G-Protein Structure

    • G-proteins: Guanine nucleotide (GTP) binding proteins
    • G-proteins are heterotrimeric, made up of 3 subunits: α, β, and γ
    • Gα: carries the binding site for the nucleotide (GDP, GTP)
    • Gβ: beta subunit
    • Gγ: gamma subunit

    GPCR Function

    • GPCR function:
      • Ligand binds to receptor at the 7-transmembrane region
      • Nucleotide exchange at the α subunit, GDP → GTP
      • Activation occurs, α subunit dissociates
      • Subunits carry on signal transduction and amplification
      • After binding to receptor is finished, signalling quantity decreases
      • α unit is favoured back to its resting conformational state (GTP → GDP)

    Active Alpha Subunit

    • The 4 names of the active alpha subunit are:
      • (names not specified)
    • These names recognise the secondary messengers they cascade

    Outcomes of Active Alpha Subunit

    • Activation of Gs or Gi active alpha subunit:
      • Adenylyl cyclase/cAMP signalling activity
    • Activation of G12/13 active alpha subunit:
      • Small GTPase families
    • Activation of Gq active alpha subunit:
      • Activates phospholipase C/IP3/DAG Signalling pathway (target enzyme)

    Beta-Gamma Subunit

    • The 3 names of the active beta-gamma subunit are:
      • (names not specified)

    Adenyl Cyclase

    • Adenyl cyclase is an enzyme that changes bonds in ATP molecule (linear → Cyclic structure)
    • Produces cAMP (secondary messenger) (can be activated/inhibited by different ligands)

    Signal Amplification

    • Signal amplification: magnifies and enhances signals received by cells, particularly during various signalling pathways
    • This amplification is essential for cells to respond effectively to extracellular stimuli and orchestrate complex cellular responses

    Calcium Regulation

    • Parathyroid hormone regulates Ca levels
    • Calcium is an essential element in the body:
      • Important role in skeletal mineralisation
      • >99% of calcium in the body is found in the bones of the skeleton
    • Hypocalcaemia: calcium levels are < 8.5 mg/dL
    • The largest concentration of calcium is found in the Endoplasmic Reticulum

    Calcium Sinks

    • Calcium sinks work by:
      • Cytoplasm/cytosol acts as a sink
      • Calcium flows from the extracellular matrix
      • Calcium flows through the cytoplasm
      • Calcium is stored in the SR/ER (smooth endoplasmic reticulum)

    Calcium Transport

    • PMCA (Ca2+ transport, ATPase):
      • Transporter that requires ATP, releases calcium from cytosol to extracellular matrix
      • Maintains low cytosolic Ca2+
    • NCX (Na+/Ca2+ exchanger):
      • Transporter mechanism from cytosol to extracellular matrix
      • No need for ATP
      • Maintains low cytosolic Ca2+
    • SERCA:
      • Transporter
      • ATP-dependent
      • Fills the smooth endoplasmic reticulum's Ca2+ storage from Cystolic Ca2+

    Mechanisms of Increasing Intracellular Ca2+

    • The 4 mechanisms/channels that increase intracellular Ca2+ are:
      • Ca2+ ion channels: selectively permeable for calcium ions
      • Voltage-gated calcium channels: open in response to cell depolarization
      • Ligand-gated ion channels: opened by ligand binding
      • Store-operated channels

    Calmodulin

    • Calmodulin is a protein that binds to calcium
    • Calmodulin has 4 binding sites for calcium
    • Calmodulin will move and activate other proteins

    Clinical Use of Calcium Channel Blockers

    • Calcium channel blockers are medications used to lower blood pressure
    • They block calcium influx, allowing blood vessels to relax and open

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    Related Documents

    Topic 2 - Intracellular Signalling Pathways PDF

    Description

    Understand the mechanisms of signal transduction, including the 4 sections: signals, receptors, transduction, and response. Learn how signals are transmitted and regulated within cells.

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