Cell-Cell Communication and Signaling
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Questions and Answers

What is a ligand in the context of cellular signaling?

  • A molecule that binds to a specific site on a protein receptor. (correct)
  • A type of intracellular receptor.
  • A molecule produced by a cell in response to a signal.
  • A relay molecule within a signal transduction pathway.

    • Which of the following is NOT typically considered a type of signal molecule?

  • Enzymes (correct)
  • Growth Factors
  • Steroids
  • Photons

    • What is the primary role of a receptor in a cell signaling pathway?

  • To activate metabolic changes directly.
  • To sense and initiate signal transduction. (correct)
  • To produce the ligand.
  • To regulate gene expression within the cell's nucleus directly.

    • Which type of receptor is most commonly found on the cell surface?

    <p>Enzyme-linked receptors</p> Signup and view all the answers

    What is the primary function of the 'transduction cascade' in cell signaling?

    <p>To relay and amplify the signal from the receptor</p> Signup and view all the answers

    What is a possible target of the signal transduction pathway?

    <p>Metabolic Enzyme</p> Signup and view all the answers

    Which of the following is a possible cellular response resulting from a signal transduction pathway?

    <p>Altered gene expression</p> Signup and view all the answers

    How do intracellular receptors such as steroid receptors differ from cell surface receptors in their mode of action?

    <p>Intracellular receptors bind to ligands that have passed through the cell membrane, and cell surface receptors bind to ligands outside the cell.</p> Signup and view all the answers

    Steroid hormones, such as testosterone, initiate cellular changes by directly interacting with what?

    <p>Specific receptor proteins within the cytoplasm</p> Signup and view all the answers

    What is the primary function of an activated hormone-receptor complex that forms in the cytoplasm?

    <p>To function as a transcription factor in the nucleus.</p> Signup and view all the answers

    What characteristic of a chemical messenger allows it to readily pass through the plasma membrane and interact with intracellular receptors?

    <p>Small and hydrophobic properties</p> Signup and view all the answers

    A mutation that prevents a hormone-receptor complex from entering the nucleus will most likely directly inhibit what process?

    <p>Gene transcription</p> Signup and view all the answers

    Which of the following is NOT a type of cell-surface receptor described in the content?

    <p>Steroid-linked</p> Signup and view all the answers

    What is the primary function of a receptor tyrosine kinase?

    <p>To phosphorylate tyrosine residues on target proteins, initiating a signaling cascade</p> Signup and view all the answers

    What event typically initiates the activation of a receptor tyrosine kinase?

    <p>The binding of a signal molecule, causing dimerization</p> Signup and view all the answers

    How many ATP molecules are required to fully activate one dimeric receptor tyrosine kinase according to the image?

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

    What is the role of the activated relay proteins in a signal transduction pathway involving receptor tyrosine kinases?

    <p>To initiate cellular responses such as changes in metabolism or gene expression</p> Signup and view all the answers

    What structural change occurs in an ion channel receptor upon ligand binding?

    <p>The central pore opens to allow passage of specific ions.</p> Signup and view all the answers

    If a ligand-gated ion channel receptor is selective for $Ca^{2+}$, what would be the consequence of its activation?

    <p>Increased concentration of $Ca^{2+}$ inside the cell</p> Signup and view all the answers

    What is the state of the ‘gate’ in an ion channel receptor when a signal molecule (ligand) is bound to its binding site?

    <p>The gate is open, allowing ions to flow across the membrane</p> Signup and view all the answers

    Which of the following is an example of a process involving a ligand-gated ion channel receptor?

    <p>Muscle contraction due to nerve signaling</p> Signup and view all the answers

    How do receptor tyrosine kinases and ion channel receptors differ from each other in their mechanisms of action?

    <p>Receptor tyrosine kinases activate a cascade of protein phosphorylation, while ion channel receptors allow passage of ions</p> Signup and view all the answers

    What is the primary role of the sodium-potassium pump (Na+/K+ ATPase)?

    <p>To create an electrochemical gradient by pumping sodium and potassium ions against their concentration gradients</p> Signup and view all the answers

    Which of the following is the immediate result of an activated G protein in the context of epinephrine signaling?

    <p>Activation of adenylyl cyclase.</p> Signup and view all the answers

    What is the role of protein kinase A in the signaling cascade?

    <p>To phosphorylate downstream target enzymes.</p> Signup and view all the answers

    What is the direct substrate of phosphorylase kinase?

    <p>Glycogen phosphorylase.</p> Signup and view all the answers

    If a cell was exposed to a molecule that inhibited adenylyl cyclase, what would be the immediate effect?

    <p>Reduction in cAMP production.</p> Signup and view all the answers

    Which of these represents the correct cascade in this signaling pathway?

    <p>G protein → adenylyl cyclase → protein kinase A → phosphorylase kinase</p> Signup and view all the answers

    What is the role of phosphatases (PP) in the context of protein phosphorylation and dephosphorylation?

    <p>To remove phosphate groups from proteins.</p> Signup and view all the answers

    What molecule directly activates glycogen phosphorylase?

    <p>Phosphorylase kinase.</p> Signup and view all the answers

    What is the effect of epinephrine binding to its receptor?

    <p>Activation of a G-protein.</p> Signup and view all the answers

    How is the signal amplified in the epinephrine cascade?

    <p>By having a single molecule activate many others down the cascade.</p> Signup and view all the answers

    What would most likely happen if phosphorylase kinase was deactivated?

    <p>Reduced breakdown of glycogen.</p> Signup and view all the answers

    What is the immediate effect of protein kinase 1 being activated?

    <p>Activation of protein kinase 2</p> Signup and view all the answers

    How many molecules of glucose-1-phosphate can be generated from 10^8 molecules of glycogen, according to the figure?

    <p>20 x 10^8</p> Signup and view all the answers

    What is the role of ATP in protein phosphorylation?

    <p>It provides the phosphate group required for phosphorylation.</p> Signup and view all the answers

    Which of the following is NOT a component of the signal amplification cascade shown?

    <p>Phospholipase C</p> Signup and view all the answers

    What is the role of active glycogen phosphorylase?

    <p>To break down glycogen</p> Signup and view all the answers

    What is the primary consequence of Vibrio cholerae enterotoxin modifying the αGs protein?

    <p>Uncontrolled activation of the Gs/cAMP signaling pathway due to blocked GTP hydrolysis.</p> Signup and view all the answers

    Which of the following best describes the action of beta-blockers regarding neurotransmitter receptors?

    <p>They have a shape similar to that of a neurotransmitter and so bind to the receptor.</p> Signup and view all the answers

    What is the role of proto-oncogenes in normal cellular function?

    <p>To promote controlled cellular growth and differentiation.</p> Signup and view all the answers

    How does a ligand-gated ion channel exemplify signal transduction?

    <p>It changes the ion concentration within the cell after binding and opening.</p> Signup and view all the answers

    What role does GTP hydrolysis play in G-protein-mediated signal transduction?

    <p>To terminate the signal by inactivating the Ga subunit.</p> Signup and view all the answers

    Which mechanisms are involved in ‘turning off’ signal transduction cascades?

    <p>Phosphodiesterase, protein phosphatases, and calcium ion pumps.</p> Signup and view all the answers

    How do many viral oncogenes cause cellular transformation?

    <p>By producing constitutively active protein kinases</p> Signup and view all the answers

    What is the significance of understanding signaling pathways in the development of cancer drugs?

    <p>To identify specific targets within tumor cell signal transduction.</p> Signup and view all the answers

    Which signaling pathway involves the activation of trimeric G-proteins and the production of second messengers like DAG and IP3?

    <p>Seven-pass membrane receptors coupled with Phospholipase C.</p> Signup and view all the answers

    Which of the following is a key function of 'c-ras family' proteins in cell signaling?

    <p>Serving as receptor-associated binding proteins.</p> Signup and view all the answers

    What role does cAMP-phosphodiesterase play in the cAMP signaling pathway?

    <p>It cleaves cAMP to terminate its signal.</p> Signup and view all the answers

    Which enzyme removes phosphate groups during signal transduction?

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

    Which of the following is a target function for Protein Kinase A in response to epinephrine?

    <p>Glycogen breakdown in muscle and liver</p> Signup and view all the answers

    What second messenger is produced by the cleavage of Phosphatidylinositol by phospholipase C?

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

    What is the role of Inositol-1,4,5-Trisphosphate (InsP3) in calcium signaling?

    <p>It activates calcium channels in the endoplasmic reticulum.</p> Signup and view all the answers

    Study Notes

    Cell-Cell Communication and Signaling

    • Cells communicate to proliferate, differentiate, migrate, and maintain a functional state
    • Cell-cell signaling coordinates functions across tissues and within the organism
    • Signaling informs cells of their role, location, and actions

    Types of Intercellular Communication

    • Endocrine: Hormones released into bloodstream, affecting distant cells
    • Paracrine: Local regulators affect nearby cells
    • Synaptic: Neurotransmitters released at synapses, affecting target cells
    • Direct contact: Cells directly connect, communicating via cytoplasm or cell junctions

    Signal Transduction Pathway

    • External signals are converted to internal responses
    • Cells receive signals from the environment (chemicals, light, sound, etc.)
    • Signal molecules (ligands) bind to receptors
    • Receptors initiate a signal transduction cascade
    • Cascades involve relay molecules that regulate target molecules
    • Target molecules produce a cellular response (e.g., altered metabolism, altered gene expression, changed cell shape/motility)

    Signal Molecules (Ligands)

    • Peptides/Proteins (e.g., growth factors)
    • Amino acid derivatives (e.g., epinephrine)
    • Small biomolecules (e.g., ATP, steroids)
    • Gases (e.g., nitric oxide)
    • Photons (like light)
    • Damaged DNA

    Receptors

    • Extracellular/Cell surface: detect hydrophilic ligands (e.g., growth factors, hormones)
      • Ion channel-linked
      • G-protein-linked (e.g., GPCRs)
      • Enzyme-linked (e.g., tyrosine kinase receptors)
    • Intracellular: detect hydrophobic ligands (e.g., steroid hormones); found inside the cell

    G-protein-linked Receptors

    • G protein acts as an on/off switch
    • GDP-bound: inactive
    • GTP-bound: active
    • Activation leads to a cascade, often involving adenyl cyclase or phospholipase C

    Adenylyl cyclase pathway

    • Activated G protein activates adenylyl cyclase
    • Adenylyl cyclase converts ATP to cyclic AMP (cAMP)
    • cAMP activates protein kinase A (PKA)
    • PKA phosphorylates target proteins, triggering a cellular response

    Phospholipase C pathway

    • Activated G protein activates phospholipase C (PLC)
    • PLC cleaves a membrane phospholipid (phosphatidylinositol 4,5-bisphosphate) into DAG & IP3
    • DAG activates protein kinase C (PKC)
    • IP3 releases Ca2+ from intracellular stores, triggering a cellular response

    Receptor Tyrosine Kinases

    • Ligand binding activates the receptor, forming a dimer
    • Tyrosine residues are phosphorylated
    • Phosphorylated tyrosines act as docking sites for intracellular signaling proteins
    • Cascades are triggered, leading to a cellular response (e.g., growth, differentiation)

    Ion Channel Receptors

    • Signal molecule (ligand) binding changes receptor shape, opening the channel
    • Specific ions (e.g., Na+, Ca2+) flow through the channel, initiating a cellular response

    Action Potential

    • Rapid, self-propagating electrical signals that transmit information in nerve cells
    • Depolarization opens voltage-gated Ca2+ channels
    • Neurotransmitter release triggers responses in target cells
    • Depolarization of the muscle cell occurs

    Protein Kinase A

    • Phosphorylates specific target proteins, leading to cellular responses
    • The phosphorylation/dephosphorylation system acts as a molecular switch

    Termination of Signaling

    • Inactivation mechanisms are crucial
    • Removal of signal molecules
    • Hydrolysis of GTP
    • Phosphodiesterase activity
    • Protein phosphatases
    • Ion pumps

    Intracellular Signaling and Diseases

    • Imbalances in signaling pathways can lead to diseases
    • Example: Cholera toxin modifies G proteins, leading to persistent activation and severe diarrhea

    Receptor Specificity

    • Cells have specific collections of proteins, determining their response to signals
    • Pathway branching and cross-talk coordinate and integrate incoming signals

    Receptor Tyrosine Kinases - Insulin Receptor

    • Insulin binds to the receptor, activating intracellular signaling pathways
    • The cascades trigger cellular responses

    Growth Factor Receptors

    • Specific growth factors activate specific receptor complexes
    • Growth factors stimulate cell growth and division

    Beta Blockers

    • Some drugs (e.g., beta blockers) mimic neurotransmitters affecting receptor response, used in treating diseases like heart failure

    General Points/Summary

    • Receptors are crucial for cell signaling
    • The shape of a signal molecule is critical in activating a receptor, and thus is essential to the lock-and-key model mentioned
    • Cancer drug therapy targets specific receptors in signaling pathways to treat cancer

    On-Line Resources

    • Relevant websites with information and resources for cell signaling studies are provided for further research

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    Cell-Cell Communication - Cell Biology MED102 PDF

    Description

    This quiz covers the mechanisms of cell-cell communication and the types of intercellular signaling. It explores how cells communicate to proliferate, differentiate, and maintain their functions through various signaling pathways. Test your knowledge on endocrine, paracrine, and synaptic signaling, as well as the processes involved in signal transduction.

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