Cell Signaling Second Messengers Quiz
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Questions and Answers

Which of the following is NOT a way that cellular messengers are regulated?

  • Chemical factors such as calcium levels in the blood
  • Endocrine factors such as thyroid stimulating hormone
  • Feedback loops used to maintain homeostasis (correct)
  • Neural factors such as autonomic stimulation of the pancreas

    • How do juxtacrine cellular messengers transmit signals between cells?

  • By binding to receptors on nearby cells
  • By being secreted and binding to the same cell's receptors
  • Through the bloodstream to distant target cells
  • Through direct cell-to-cell contact-dependent signaling (correct)

    • Which type of cellular messenger is responsible for communication within the immune system?

  • Hormones
  • Cytokines (correct)
  • Second messengers
  • Neurotransmitters

    • Which of the following is a key function of feedback loops in regulating cellular messengers?

    <p>To maintain a constant level of messengers</p> Signup and view all the answers

    What is the primary method by which endocrine cellular messengers, or hormones, are transported to target cells?

    <p>Via the bloodstream to distant target cells</p> Signup and view all the answers

    Which cellular response to messengers involves activating preexisting proteins through a second messenger system?

    <p>Activating preexisting proteins through a second messenger system</p> Signup and view all the answers

    What type of messengers are often made on-demand because they cannot be stored?

    <p>Lipid-soluble messengers</p> Signup and view all the answers

    Which type of messengers are synthesized from cholesterol?

    <p>Sex hormones</p> Signup and view all the answers

    What do water-soluble 1st messengers interact with to initiate the signaling pathway?

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

    In cell-to-cell communication, what is activated by the hormone messenger to produce the primary effector that leads to the creation of the 2nd messenger?

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

    What is the primary mechanism by which interstitial fluid and plasma regulate fluid movement and balance?

    <p>Capillary hydrostatic pressure (CHP) forces water out from the capillary into the interstitial space</p> Signup and view all the answers

    What is the main driving force for movement of water between the interstitial fluid (IF) and intracellular fluid (ICF)?

    <p>Osmotic forces</p> Signup and view all the answers

    Which electrolyte is the most abundant cation in the extracellular fluid (ECF)?

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

    What happens to a cell in a hypertonic solution?

    <p>Water moves out of the cell and the cell shrinks</p> Signup and view all the answers

    What is the defining characteristic of an isotonic change in total body water (TBW)?

    <p>Changes in TBW are accompanied by a proportional change in concentration of electrolytes</p> Signup and view all the answers

    Which of the following statements accurately describes the role of G-protein coupled receptors (GPCRs) in cellular signaling?

    <p>GPCRs are membrane-bound receptors that activate second messengers like cAMP and calcium upon binding to first messengers.</p> Signup and view all the answers

    Which of the following statements accurately describes the role of calcium as a second messenger in cellular signaling?

    <p>Calcium is stored in the endoplasmic reticulum and is released into the cytosol to elicit cellular responses like muscle contraction and neuronal activation.</p> Signup and view all the answers

    Which of the following statements accurately describes the difference between lipid-soluble and water-soluble messengers in cellular signaling?

    <p>Lipid-soluble messengers target intracellular receptors and regulate protein synthesis, while water-soluble messengers interact with membrane-bound receptors and activate second messengers.</p> Signup and view all the answers

    Which of the following statements accurately describes the role of proteolytic cascades in cellular signaling?

    <p>Proteolytic cascades, such as the coagulation cascade, facilitate signal transduction and amplification through sequential activation of proteolytic enzymes.</p> Signup and view all the answers

    Which of the following statements accurately describes the role of feedback loops in cellular signaling?

    <p>Feedback loops are mechanisms by which the products or downstream effects of a signaling pathway can regulate the activity of upstream components, providing a means of modulating the signaling response.</p> Signup and view all the answers

    Which of the following is a key mechanism by which external/environmental factors can influence cellular processes regulated by the cell membrane?

    <p>Modifying the expression of membrane-bound receptor proteins</p> Signup and view all the answers

    The sodium-potassium pump is an example of which type of membrane transport mechanism?

    <p>Active transport</p> Signup and view all the answers

    Which of the following is a key function of feedback loops in regulating cellular messengers?

    <p>Decreasing the sensitivity of target cells to cellular messengers</p> Signup and view all the answers

    Which type of cellular messenger is responsible for communication between cells that are in direct physical contact?

    <p>Juxtacrine messengers</p> Signup and view all the answers

    Which of the following is NOT a way that cellular messengers are regulated?

    <p>Altering the distribution of messenger molecules within the cell</p> Signup and view all the answers

    Which of the following is a key way that juxtacrine cellular messengers transmit signals between cells?

    <p>By directly binding to receptors on the surface of target cells</p> Signup and view all the answers

    Which of the following is the primary mechanism by which endocrine cellular messengers, or hormones, are transported to target cells?

    <p>Vesicular transport within the bloodstream</p> Signup and view all the answers

    Which type of cellular messenger is responsible for communication within the immune system?

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

    Which of the following is a key function of feedback loops in regulating cellular messengers?

    <p>Decreasing the sensitivity of target cells to cellular messengers</p> Signup and view all the answers

    Which of the following is NOT a way that cellular messengers are regulated?

    <p>Altering the distribution of messenger molecules within the cell</p> Signup and view all the answers

    What is the main function of cellular messenger receptors in target cells?

    <p>Initiate signal transduction upon hormone binding</p> Signup and view all the answers

    Which type of hormones can easily diffuse across the plasma membrane?

    <p>Lipid-soluble hormones</p> Signup and view all the answers

    How do low concentrations of hormones affect cellular messenger receptors?

    <p>Increase the number of receptors per cell</p> Signup and view all the answers

    Which process is associated with the transport of water-soluble hormones?

    <p>Being bound to carrier proteins</p> Signup and view all the answers

    What happens when a target cell has more cellular messenger receptors?

    <p>The cell becomes more sensitive to hormones</p> Signup and view all the answers

    Which of the following processes is primarily responsible for the rapid regulation of blood pH in response to changes in CO2 levels?

    <p>Respiratory regulation of CO2 removal through exhalation</p> Signup and view all the answers

    What is the primary role of the carbonic acid-bicarbonate buffer system in regulating blood pH?

    <p>Maintaining the narrow pH range required for optimal enzyme function</p> Signup and view all the answers

    In the context of cell-to-cell communication, which of the following best describes the role of hemoglobin in regulating pH?

    <p>It serves as a buffer to maintain pH within red blood cells</p> Signup and view all the answers

    What is the primary mechanism by which the kidneys contribute to the regulation of blood pH?

    <p>Reabsorbing bicarbonate and excreting hydrogen ions in the urine</p> Signup and view all the answers

    Which of the following best describes a feedback loop involved in the regulation of blood pH?

    <p>A decrease in bicarbonate levels triggers the kidneys to reabsorb more bicarbonate</p> Signup and view all the answers

    Which type of cellular messengers are often synthesized on-demand because they cannot be stored?

    <p>Lipid-soluble messengers</p> Signup and view all the answers

    What is the primary mechanism by which $G$-protein coupled receptors (GPCRs) transmit signals in cellular communication?

    <p>Activating preexisting proteins through a second messenger system</p> Signup and view all the answers

    What happens to the number of cellular messenger receptors when hormone concentrations are high?

    <p>The number of receptors decreases</p> Signup and view all the answers

    Which of the following is a key mechanism by which lipid-soluble messengers, such as hormones, influence cellular processes?

    <p>Binding to intracellular receptors and activating RNA polymerase</p> Signup and view all the answers

    What is the primary function of second messengers in cellular communication?

    <p>To amplify and propagate the signal initiated by the first messenger</p> Signup and view all the answers

    Which of the following is NOT a characteristic of water-soluble messengers in cellular signaling?

    <p>Target intracellular receptors</p> Signup and view all the answers

    What is the primary function of proteolytic cascades in cellular communication?

    <p>Amplify signal transduction</p> Signup and view all the answers

    In cellular signaling, what initiates the creation of the second messenger within a target cell?

    <p>GPCR activation</p> Signup and view all the answers

    Which process can be activated by increased concentrations of calcium in the ICF?

    <p>Muscle contraction</p> Signup and view all the answers

    What is a direct consequence of releasing calcium from endoplasmic reticulum stores?

    <p>Increase in ICF calcium levels</p> Signup and view all the answers

    What is the primary mechanism by which lipid-soluble hormones initiate cellular signaling in target cells?

    <p>Binding to intracellular receptors and directly regulating gene transcription</p> Signup and view all the answers

    Which of the following best describes the function of negative feedback loops in the regulation of cellular messengers?

    <p>Terminate the signal once a specific threshold is reached</p> Signup and view all the answers

    Which of the following processes is primarily responsible for the transport of water-soluble hormones to target cells?

    <p>Circulation in free, unbound form through the bloodstream</p> Signup and view all the answers

    What is the primary mechanism by which up-regulation of cellular messenger receptors occurs in response to low hormone concentrations?

    <p>Increased synthesis of new receptors by ribosomes</p> Signup and view all the answers

    Which of the following best describes the role of positive feedback loops in cellular signaling?

    <p>Amplify the initial signal to maintain a sustained response</p> Signup and view all the answers

    What is the primary mechanism by which external/environmental factors can influence cellular processes regulated by the cell membrane?

    <p>Altering the activity of membrane transporters and channels</p> Signup and view all the answers

    Which type of cellular messenger is responsible for rapid, short-term communication between cells that are in direct physical contact?

    <p>Juxtacrine messengers</p> Signup and view all the answers

    What is the primary driving force for the movement of water between the intracellular fluid (ICF) and extracellular fluid (ECF)?

    <p>Osmotic pressure gradient</p> Signup and view all the answers

    Which type of cellular messenger is responsible for long-range communication between cells throughout the body?

    <p>Endocrine messengers</p> Signup and view all the answers

    Which type of membrane transport mechanism is driven by the electrochemical gradient, rather than directly by ATP hydrolysis?

    <p>Secondary active transport</p> Signup and view all the answers

    What is the primary mechanism by which lipid-soluble cellular messengers cross the cell membrane to reach their target receptors?

    <p>They simply diffuse across the lipid bilayer</p> Signup and view all the answers

    Which of the following statements accurately describes the role of proteolytic cascades in cellular signaling?

    <p>They amplify the signal by sequentially activating multiple proteins</p> Signup and view all the answers

    What is the primary mechanism by which water-soluble messengers initiate cellular responses?

    <p>They interact with membrane-bound receptors that activate second messengers</p> Signup and view all the answers

    Which of the following best describes the role of desensitization in the regulation of cellular messenger responses?

    <p>It reduces the number of active receptors on the cell surface</p> Signup and view all the answers

    Which of the following processes is primarily responsible for the rapid regulation of blood pH in response to changes in $CO_2$ levels?

    <p>Respiratory regulation of $CO_2$ levels</p> Signup and view all the answers

    Which type of cellular messengers are synthesized on-demand because they cannot be stored?

    <p>Water-soluble messengers</p> Signup and view all the answers

    What is the primary function of second messengers in cellular communication?

    <p>Activating preexisting proteins through a second messenger system</p> Signup and view all the answers

    Which type of messengers are synthesized from cholesterol?

    <p>Lipid-soluble messengers</p> Signup and view all the answers

    What is the primary role of the carbonic acid-bicarbonate buffer system in regulating blood pH?

    <p>Rapid regulation of blood pH in response to CO2 levels</p> Signup and view all the answers

    In cell-to-cell communication, what is activated by the hormone messenger to produce the primary effector for the creation of second messengers?

    <p>Extracellular matrix (ECM)</p> Signup and view all the answers

    What happens to the number of cellular messenger receptors when hormone concentrations are high?

    <p>Increase to enhance cell response</p> Signup and view all the answers

    Which type of hormones can easily diffuse across the plasma membrane?

    <p>Water-soluble hormones</p> Signup and view all the answers

    Which of the following cellular messengers is responsible for communication within the immune system?

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

    What is the primary mechanism by which endocrine cellular messengers, or hormones, are transported to target cells?

    <p>Through the bloodstream</p> Signup and view all the answers

    Which of the following processes is associated with the creation of ATP, the primary energy currency of the cell?

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

    Which type of cellular messenger is responsible for local, short-range communication between neighboring cells?

    <p>Paracrine messengers</p> Signup and view all the answers

    What is a key function of feedback loops in regulating the release of cellular messengers?

    <p>To maintain a constant level of messengers in the body</p> Signup and view all the answers

    Study Notes

    Regulation of Messenger Release

    • Negative feedback loop: a common mechanism in the endocrine system that prevents overproduction of hormones
    • Positive feedback loop: an uncommon mechanism that amplifies a response, examples include contractions during childbirth, stimulation of milk production, and trigger of ovulation

    Cellular Messenger Transport

    • Messengers (hormones) are released into the circulatory system by endocrine glands and distributed throughout the body
    • Water-soluble hormones circulate in free, unbound forms
    • Lipid-soluble hormones are primarily transported bound to a carrier or transport protein

    Cellular Messenger Receptors

    • Target cells recognize and bind with a high affinity to specific hormones
    • Receptors initiate a signal, and the more receptors, the more sensitive the cell
    • Receptors are located in or on the plasma membrane or in the intracellular compartment of the target cell
    • Water-soluble hormones cannot diffuse across the plasma membrane, while lipid-soluble hormones can diffuse across the plasma membrane and bind to cytosolic or nuclear receptors

    Up- and Down-Regulation of Receptors

    • Up-regulation: low concentrations of hormones increase the number of receptors per cell
    • Down-regulation: high concentrations of hormones decrease the number of receptors per cell

    Effects of Cellular Messengers

    • Three cellular responses to messengers:
      1. Act on preexisting channel-forming proteins to alter membrane channel permeability
      2. Activate preexisting proteins through a second messenger system
      3. Activate or suppress protein synthesis

    Lipid-Soluble Messengers

    • Lipid-soluble messengers are often made on-demand because they cannot be stored
    • Synthesized from cholesterol
    • Examples: sex hormones, steroids, vitamin D, retinoid, thyroxine, and arachidonic acid derivatives
    • Activate RNA polymerase and DNA transcription

    Water-Soluble Messengers

    • Water-soluble 1st messengers: extracellular molecules that initiate signaling pathways and interact with a receptor
    • Examples: peptides, glycoproteins, polypeptides, and amines
    • 2nd messengers: intracellular molecules activated by 1st messenger, which in turn activate kinases that lead to cellular response
    • Activate G-protein to produce primary effector, which leads to the creation of 2nd messenger

    G Protein-Coupled Receptor (GPCR)

    • Image Credit: 2002 Nature Publishing Group, Li, J.

    Cellular Metabolism

    • Cellular metabolism: creation of ATP from chemical energy contained in organic molecules
    • Two types of cellular metabolism: catabolism (breaks down molecules to create energy) and anabolism (uses energy to synthesize molecules)
    • Processes: glycolysis, oxidative decarboxylation, citric acid cycle, oxidative phosphorylation
    • Dysfunction in metabolism can result in profound disease

    Cellular Communication

    • Cellular communication: cells transmit messages to other cells through chemical messengers
    • Categories of cellular messengers: endocrine (uses bloodstream to send signals), paracrine (local action), autocrine (cell secretes and responds to its own messengers), and juxtacrine (cell-to-cell contact-dependent)
    • Regulation of messenger release: chemical, endocrine, and neural factors

    Effects of Cellular Messengers

    • Three cellular responses to messengers:
      1. Act on preexisting channel-forming proteins to alter membrane channel permeability
      2. Activate preexisting proteins through a second messenger system
      3. Activate or suppress protein synthesis

    Second Messengers

    • Cyclic AMP (cAMP): a common second messenger
    • Calcium: a second messenger that can be increased via releasing ER stores or allowing calcium from ECF into the ICF

    Proteolytic Cascades

    • Coagulation cascade: a proteolytic cascade that regulates blood clotting

    Cell Membrane

    • Cell membrane: a phospholipid bilayer that maintains the distinction between internal and external cellular environments
    • Function: due to the chemical properties of the bilayer (hydrophobic tails and hydrophilic heads)
    • Important functions: transportation of polar substances, cell adhesion, and cell signaling

    Membrane Transport

    • Types of membrane transport: passive, active, and facilitated diffusion
    • Passive transport: no energy required, includes diffusion, osmosis, and facilitated diffusion
    • Active transport: requires energy, includes pumps and co-transport
    • Facilitated diffusion: uses transport proteins, includes channel-mediated and carrier-mediated transport

    Resting Membrane Potential

    • Resting membrane potential (RMP): an electrochemical gradient across the cell membrane
    • Established by membrane pumps and channels
    • Important for neuronal activation and muscle contraction

    Buffer Systems

    • Function: maintain homeostasis within a narrow pH range
    • Acids: molecules that can donate a proton (H+)
    • Bases: molecules that can accept a proton (H+)
    • Buffer systems: prevent large changes in pH, examples include carbonic acid-bicarbonate buffer and phosphate buffer
    • Importance: enzymes lose efficacy outside of the narrow pH range, and direct cellular injury and death can occur outside of this range### Cell Transport
    • Cell transport can be either passive or active
    • Active transport requires energy
    • Active transporters can fuel other transporters in the form of stored energy
    • Maintaining the extracellular and intracellular environments through transport mechanisms is vital to a number of biological functions
    • Potassium gradient (and to a lesser degree sodium) as established by the sodium potassium pump is essential for the resting membrane potential

    Cell Adhesion

    • Cell adhesion mechanisms include:
      • Extracellular matrix (ECM)
      • Cell-adhesion molecules (CAMs)
      • Specialized cell junctions
    • Extracellular matrix (ECM):
      • Molecular network that creates structure and support for cells
      • Participates in regulating cell growth
      • Comprised of:
        • Basement membrane
        • Glycoproteins/proteoglycans
        • Non-proteoglycan polysaccharides
        • Interstitial proteins
        • Matrix minerals
      • Functions:
        • Stores growth factors
        • Hydrates cells
        • Contributes to tensile strength of tendons, ligaments, and cartilage
    • Cell-adhesion molecules (CAMs):
      • Four different families: Cadherins, Selectins, Ig Superfamily, Integrins
      • Mechanical attachment between cell and ECM
    • Specialized cell junctions:
      • Desmosomes: physical attachment
      • Tight Junctions: barrier
      • Gap Junctions: allow cell-to-cell transport

    Cellular Communication

    • Cellular communication involves ligands binding to receptors on/in a target cell to elicit a response
    • Types of communication based on distance traveled from signal cell to target cell:
      • Lipid-soluble messengers target intracellular receptors
      • Water-soluble messengers (1st messengers) interact with membrane-bound receptors on a target cell
      • Signal transduction and amplification is an important function of proteolytic cascades

    Cell Membrane

    • Cell membrane is a phospholipid bilayer that maintains the distinction between the internal and external cellular environments
    • Function is due to the chemical properties of the bilayer (hydrophobic tails and hydrophilic heads) that allow diffusion of non-polar substances but not polar substances
    • Proteins on/in the membrane perform important functions like:
      • Transportation of polar substances
      • Cell adhesion
      • Cell signaling

    Membrane Transport

    • Passive transport:
      • Diffusion: non-polar substances
      • Facilitated diffusion: polar substances
      • Osmosis: movement of water through a semipermeable membrane
    • Active transport:
      • Pumps: Na/K pump, Cotransport
      • Requires energy
      • Brings other substances into the cell against their concentration gradients
    • Secondary active transport:
      • Energy derived from “stored” energy as opposed to directly from the breakdown of ATP

    Cellular Metabolism

    • ATP is created from chemical energy contained in organic molecules:
      • Carbohydrates
      • Lipids
      • Proteins
    • Used in synthesis of organic molecules, muscle contraction, and active transport
    • Functions as a way to store and transfer energy
    • Catabolism (breaks down molecules to create energy) and anabolism (uses energy to build molecules)
    • Processes that create ATP:
      • Glycolysis
      • Oxidative decarboxylation (pyruvate)
      • Citric acid cycle
      • Oxidative phosphorylation
    • Dysfunction in metabolism can result in profound disease, such as phenylketonuria

    Cellular Messengers and Receptors

    • Cellular messengers (also called chemical messengers):
      • Created in response to a specific stimulus
      • Travel to a target cell to elicit a response
      • Categories:
        • Endocrine (uses blood stream to send signals far away)
        • Paracrine (local action, influences nearby cells)
        • Autocrine (cell secretes a chemical messenger that binds to its own receptors)
        • Juxtacrine (cell-to-cell contact-dependent)
    • Regulation of messenger release:
      • Chemical factors (e.g., calcium levels in the blood)
      • Endocrine factors (e.g., thyroid-stimulating hormone)
      • Neural factors (e.g., autonomic stimulation of pancreas)
      • Feedback loops to maintain homeostasis

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