Cell Signalling and Transmembrane Receptors in Biochemistry
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Questions and Answers

What is the primary function of transmembrane receptors in cellular signalling?

  • To activate gene expression in response to extracellular signals (correct)
  • To facilitate the breakdown of glycogen in the liver
  • To synthesise glucagon in response to adrenaline
  • To release histamine from mast cells

    • Which of the following is NOT an example of a second messenger?

  • Diacylglycerol
  • cAMP
  • Glucagon (correct)
  • Inositol triphosphate (IP3)

    • What is the primary function of G proteins in signal transduction pathways?

  • To transmit signals from transmembrane receptors to intracellular signalling pathways (correct)
  • To stimulate the release of histamine from mast cells
  • To activate receptor tyrosine kinases
  • To synthesise prostaglandins from arachidonic acid

    • Which of the following is an example of a cellular response to extracellular signals?

    <p>Change in gene expression in response to EGF</p> Signup and view all the answers

    What is the role of phospholipase C in signal transduction pathways?

    <p>To cleave phosphatidylinositol 4,5-bisphosphate (PIP2) into diacylglycerol and inositol triphosphate (IP3)</p> Signup and view all the answers

    Which of the following is an example of an extracellular signal that binds to a transmembrane receptor?

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

    What is the role of Receptor Tyrosine Kinase (RTK) in signal transduction pathways?

    <p>To activate downstream signalling pathways by phosphorylating target proteins</p> Signup and view all the answers

    Which of the following is an example of a cellular response to extracellular signals that involves changes in gene expression?

    <p>Epithelial cell differentiation in response to EGF</p> Signup and view all the answers

    What is the primary characteristic of a paracrine signal?

    <p>The signal acts on other cells that are very close to the producing cell.</p> Signup and view all the answers

    Which type of receptor is typically associated with hydrophilic hormones such as adrenaline?

    <p>Cell surface receptor</p> Signup and view all the answers

    What is the primary difference between autocrine and paracrine signaling?

    <p>The distance the signal travels to reach its target cells.</p> Signup and view all the answers

    What is a characteristic of receptors in terms of their binding to signals?

    <p>They have high selectivity and high affinity.</p> Signup and view all the answers

    Which type of signaling involves the direct interaction between two cells?

    <p>Contact-dependent signaling</p> Signup and view all the answers

    What is a characteristic of signals in terms of their binding to different receptors?

    <p>They can bind to different types of receptors with high affinity.</p> Signup and view all the answers

    What is the primary mechanism of action for steroid hormones?

    <p>Binding to a receptor in the cytosol and triggering a response inside the cell</p> Signup and view all the answers

    What is the effect of acetylcholine binding to its receptor?

    <p>Depolarization of the plasma membrane due to the flow of ions</p> Signup and view all the answers

    What is the function of the DNA binding domain in steroid hormones?

    <p>To bind to hormone response elements in the sequence of target genes</p> Signup and view all the answers

    What is the role of G-protein-coupled receptors in signaling pathways?

    <p>To generate a secondary message inside the cell through cyclic AMP</p> Signup and view all the answers

    What is the effect of glucagon binding to its receptor?

    <p>Generation of a secondary message inside the cell through cyclic AMP</p> Signup and view all the answers

    What is the function of the hormone binding domain in steroid hormones?

    <p>To interact with other transcription factors</p> Signup and view all the answers

    What is the effect of EGF binding to its receptor?

    <p>Activation of an enzymatic kinase cascade through the MAP kinase pathway</p> Signup and view all the answers

    What is the role of phospholipase C in signaling pathways?

    <p>To generate inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol (DAG)</p> Signup and view all the answers

    What is the main function of the G-protein α subunit when GTP is bound to it?

    <p>It dissociates from the βγ subunit and activates the effector enzyme</p> Signup and view all the answers

    What is the result of the GTPase activity on the G-protein α subunit?

    <p>The G-protein α subunit becomes inactive and re-associates with the βγ subunit</p> Signup and view all the answers

    What is the function of the βγ subunit in the G-protein complex?

    <p>It plays a crucial role in the GTP/GDP exchange on the G-protein</p> Signup and view all the answers

    What is the result of the signal binding to the receptor in GPCR signalling?

    <p>The G-protein α subunit becomes active and activates the effector enzyme</p> Signup and view all the answers

    What is the function of the effector enzyme in GPCR signalling?

    <p>It produces the 2nd messenger that triggers the downstream response</p> Signup and view all the answers

    What is the purpose of the GTP/GDP exchange on the G-protein?

    <p>It allows the G-protein to switch between its active and inactive states</p> Signup and view all the answers

    What is the outcome of GTP hydrolysis in the G-protein complex?

    <p>G-protein complex re-association</p> Signup and view all the answers

    What is the role of cAMP in the activation of protein kinase A (PKA)?

    <p>cAMP binds to the regulatory subunit of PKA</p> Signup and view all the answers

    What is the effect of phosphorylase kinase a on glycogen?

    <p>It phosphorylates glycogen, converting it to glucose-1-phosphate</p> Signup and view all the answers

    What is the role of phosphodiesterase in the regulation of cAMP levels?

    <p>It hydrolyzes cAMP to AMP</p> Signup and view all the answers

    What is the outcome of CREB phosphorylation by PKA?

    <p>It activates transcription by binding to specific sequences</p> Signup and view all the answers

    What is the outcome of IP3 binding to the Ca2+ channel in the endoplasmic reticulum?

    <p>It activates the release of Ca2+ into the cytosol</p> Signup and view all the answers

    What is the role of DAG in the activation of protein kinase C?

    <p>It binds to protein kinase C, making it more active</p> Signup and view all the answers

    What is the outcome of signal amplification via kinase cascade?

    <p>A small signal is amplified to a large response</p> Signup and view all the answers

    What is the role of Gαq (Gq) subunit in the GPCR pathway?

    <p>It activates phospholipase C, leading to the production of IP3 and DAG</p> Signup and view all the answers

    What is the outcome of the binding of cAMP to the regulatory subunit of PKA?

    <p>The tetramer dissociates, and the catalytic subunits are activated</p> Signup and view all the answers

    Study Notes

    Cell Biology and Signalling

    • The course covers the foundations of medical science, specifically cell biology and signalling.

    Cellular Responses

    • Cellular responses to signals include:
      • Change in metabolic activities (e.g. glucagon switches liver from synthesizing glycogen to breaking down glycogen)
      • Secrete and release (e.g. binding of antigen to mast cell stimulates the secretion of histamine)
      • Changes in gene expression (e.g. Epidermal Growth Factor (EGF) activating genes involved in cell growth)
      • Sensory perception (e.g. light activation of rhodopsin)

    Extracellular Signals

    • Factors that act as extracellular signals include:
      • Amino acids (and derivatives) (e.g. glutamate, adrenaline, dopamine)
      • Steroids (e.g. oestradiol, testosterone, cortisol, aldosterone)
      • Prostaglandins (eicosanoids) derived from arachidonic acid
      • Proteins and Peptides (e.g. insulin, glucagon, growth factor, EGF)
      • Gases (e.g. NO, CO)

    Ways for Cells to Signal to Each Other

    • Different ways for cells to signal to each other include:
      • Endocrine (signal produced by cells in one part of the body and travels in blood to target cells somewhere else)
      • Autocrine (signal acts on the same cell that produces it)
      • Paracrine (signal produced by cell and acts on other cells that are very close)
      • Contact dependent (signal is integral part of one cell and interacts directly with another cell)
      • Neuronal (electrical signal transmitted down cell and message passed to another via synapse)

    Receptor/Signal

    • A cell must express a receptor in order to respond to a signal
    • Receptors have high selectivity and high affinity
    • Signals can bind to different types of receptors
    • Signals are eventually turned off

    Location of Receptors

    • Cell surface receptors (e.g. hormone is hydrophilic, binding of hormone triggers response inside cell)
    • Intracellular receptors (e.g. hormone is hydrophobic, hormone crosses the plasma membrane, hormone binds to receptor in the cytosol and triggers a response inside cell)

    Types of Signalling

    • Binding of signal to receptor:
      • Depolarization of membrane due to flow of ions (e.g. acetylcholine)
      • Direct activation of transcription factor (e.g. steroid)
      • Generation of secondary message inside cell (e.g. glucagon – cAMP)
      • Direct activation of enzymatic kinase cascade (e.g. EGF – MAP kinase pathway)

    Second Messengers

    • Cyclic AMP (cAMP)
    • Cyclic GMP (cGMP)
    • Inositol 1, 4, 5-trisphosphate (IP3)
    • Diacylglycerol (DAG)
    • Calcium ions (Ca2+)

    G-Protein-Coupled Receptors

    • G-protein-coupled receptors (GPCRs) have 7 transmembrane-spanning domains
    • Activation of GPCRs leads to the activation of G-proteins
    • G-proteins are guanine nucleotide binding proteins

    G-Protein Signalling

    • G-protein signalling involves:
      • Signal binding to receptor
      • G-protein (GDP bound) associates with receptor
      • GTP/GDP exchange on G-protein (GTP bound)
      • G-protein dissociates into α (GTP bound) and βγ subunits
      • α subunit (with GTP bound) activates effector enzyme
      • Effector enzyme produces 2nd messenger
      • GTP hydrolysed to GDP, G-protein complex re-associates, signalling ends

    cAMP Signalling

    • cAMP is a second messenger produced by the activation of adenylyl cyclase
    • cAMP activates protein kinase A (PKA)
    • PKA phosphorylates and activates target proteins

    cAMP Dependent Protein Kinase A (PKA)

    • PKA is a tetrameric enzyme consisting of 2 regulatory (R) and 2 catalytic (C) subunits
    • cAMP binds to the regulatory subunit and tetramer dissociates
    • Catalytic monomers (C) are now active enzymes

    cAMP Mediated Effects on Glycogen Breakdown

    • cAMP dependent protein kinase (PKA) phosphorylates and activates phosphorylase kinase
    • Phosphorylase kinase phosphorylates and activates phosphorylase
    • Phosphorylase breaks down glycogen to glucose-1-phosphate

    Signal Amplification via Kinase Cascade

    • Signal amplification occurs through the activation of multiple enzymes in a kinase cascade
    • The numbers of molecules involved in each step of the cascade increase, amplifying the signal

    cAMP and Gene Transcription

    • PKA phosphorylates CREB (cAMP response element binding protein)
    • CREB binds to specific sequences in target genes and stimulates transcription
    • Long-term adaptation to starvation involves changes in gene expression

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    Description

    Quiz on cell biology and signalling, covering cell-to-cell signalling, second messengers, and transmembrane receptors in biochemistry.

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