Cell signalling
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Questions and Answers

What is the first step in the process of cell signaling?

  • Respond to signal
  • Transduce the signal
  • Receive the signal (correct)
  • Convert the signal to intracellular info
  • Which type of signaling involves cells communicating over short distances using secreted messenger molecules?

  • Paracrine signaling (correct)
  • Juxtracrine signaling
  • Autocrine signaling
  • Endocrine signaling
  • What type of receptors can trigger multiple signal transduction pathways at once?

  • Intracellular receptors
  • G protein-coupled receptors
  • Ion channel receptors
  • Receptor tyrosine kinases (correct)
  • Which process describes signaling between the same cell?

    <p>Autocrine signaling (D)</p> Signup and view all the answers

    What is a defining feature of G protein-coupled receptors?

    <p>They associate with a G protein (A)</p> Signup and view all the answers

    What is required for a cell to respond to a specific signal?

    <p>The presence of a receptor specific to that signal (A)</p> Signup and view all the answers

    Which of the following is NOT a type of membrane receptor?

    <p>Intracellular receptors (D)</p> Signup and view all the answers

    What does cortisol primarily aid in regarding metabolism?

    <p>Increasing blood sugar through gluconeogenesis (B)</p> Signup and view all the answers

    What is the primary role of a kinase enzyme in cell signaling?

    <p>To add a phosphate group to a target protein (D)</p> Signup and view all the answers

    What happens when a ligand binds to a ligand-gated ion channel?

    <p>It induces a shape change allowing specific ions to flow (B)</p> Signup and view all the answers

    How do intracellular receptors operate when activated by small hydrophobic chemical messengers?

    <p>They directly alter gene expression as transcription factors (D)</p> Signup and view all the answers

    In signal transduction, what is the significance of protein phosphorylation?

    <p>It represents a mechanism for regulating protein activity (B)</p> Signup and view all the answers

    Which of the following is NOT a common second messenger in signaling pathways?

    <p>ATP (D)</p> Signup and view all the answers

    What initiates the activation of protein kinase A (PKA) in a signaling pathway involving cyclic AMP?

    <p>Conversion of ATP to cAMP (C)</p> Signup and view all the answers

    What is the primary consequence of increased calcium ion concentrations in animal cells?

    <p>Secretion of substances and cell division (D)</p> Signup and view all the answers

    What occurs during the nuclear response of a signal transduction pathway?

    <p>Gene expression is regulated through transcription factors (D)</p> Signup and view all the answers

    Why is signaling termination important in cellular pathways?

    <p>It allows cells to remain responsive to new signals (D)</p> Signup and view all the answers

    What would likely happen if molecular changes in signaling pathways became locked in one state?

    <p>The cell might exhibit disrupted functions (D)</p> Signup and view all the answers

    Flashcards

    Paracrine signaling

    A form of cell communication where a signal is sent from one cell to another through the secretion of messenger molecules that travel short distances. An example of this is growth factors, which stimulate local cells to grow and divide.

    Endocrine signaling

    A long-distance form of cell signaling where specialized cells release hormones that travel through the circulatory system to reach target cells.

    Juxtacrine signaling

    A type of cell signaling where cells communicate directly through contact, without the need for secreted signaling molecules.

    Receptors

    Cellular proteins that bind specifically to signaling molecules (ligands) and initiate a cellular response. They are often located either on the cell surface or within the cytoplasm.

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    Signal transduction

    The process by which a cell converts an extracellular signal into an intracellular response.

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    Receptor tyrosine kinases (RTKs)

    A class of membrane receptors that attach phosphate groups to tyrosine amino acids. They can activate multiple signal transduction pathways simultaneously, allowing for complex and coordinated cellular responses.

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    G-protein-coupled receptors (GPCRs)

    A large family of cell-surface receptors that associate with G proteins. They bind a diverse range of signaling molecules, including neurotransmitters and hormones.

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    Ion channel receptors

    A type of membrane receptors that allow the passage of ions across the cell membrane in response to a specific signal. They play a crucial role in processes such as nerve impulse transmission.

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    Ligand-gated ion channel

    A type of membrane receptor that acts as a gate, opening only when a specific ligand binds. This change allows specific ions to flow, affecting the cell's activity.

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    Intracellular receptor

    Proteins located in the cytoplasm or nucleus that bind to small, hydrophobic messengers like steroid and thyroid hormones. This allows these messengers to cross the membrane and activate the receptor.

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    Protein phosphorylation

    A widespread cellular method for regulating protein activity. Protein kinases add phosphates to proteins from ATP, while phosphatases remove phosphates.

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    Second messengers

    Small, non-protein molecules or ions that spread by diffusion and participate in signaling pathways. Examples include cAMP and calcium ions.

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    Cyclic AMP (cAMP)

    A type of second messenger that activates protein kinase A. It is produced by adenylyl cyclase converting ATP to cAMP.

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    Calcium ions (Ca2+)

    Another common second messenger that often increases in concentration due to external signals. Its increase can trigger various cellular responses including muscle contraction, secretion, and cell division.

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    Cellular response

    The final response of a cell to a signal. This response can occur in the cytoplasm or the nucleus, affecting enzyme activity, opening of ion channels, or gene expression.

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    Nuclear response

    A signaling pathway that regulates the synthesis of enzymes or other proteins by turning genes on or off in the nucleus. Activated receptors can act as transcription factors.

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    Signalling termination

    The process of stopping a signal transduction pathway. This is crucial to prevent overstimulation and ensure cell function. Inactivation mechanisms are just as important as activation.

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    Study Notes

    Cell Signaling Overview

    • Cell signaling is a complex communication system that governs cellular activities
    • Cells receive, transduce, and respond to signals
    • Signals can be proteins, peptides, small molecules, or inorganic ions
    • Types of signaling: autocrine (same cell), paracrine (nearby cell), endocrine (distant cell), juxtacrine (cell contact dependent)

    Paracrine Signaling

    • Local signaling using secreted messenger molecules over short distances
    • Growth factors (cytokines) are examples

    Endocrine Signaling

    • Long-distance signaling using hormones
    • Specialized cells release hormones into the circulatory system to target distant cells
    • Cellular response depends on receptor presence

    Receptor Classification

    • Receptors are categorized as intracellular or cell surface
    • Intracellular receptors: in cytoplasm or nucleus, suitable for lipophilic signals
    • Cell surface receptors: on the plasma membrane, for hydrophilic signals.

    Receptor Types

    • G protein-coupled receptors (GPCRs): largest family, associate with G proteins. Bind various signals like epinephrine and neurotransmitters
    • Receptor tyrosine kinases (RTKs): phosphorylate tyrosine residues, trigger multiple pathways affecting growth and reproduction. Abnormal RTK function can cause cancer.
    • Ligand-gated ion channels: act as gates responding to ligand binding, allow ion flow, regulate cell activities

    Intracellular Receptors

    • Located in the cytoplasm or nucleus.
    • Small, hydrophobic signals like steroid and thyroid hormones cross the membrane and bind.

    Signal Transduction

    • Signal binding triggers a cascade of conformational changes. Often involves phosphorylation.
    • Second messengers: small, non-protein, water-soluble molecules (e.g., cAMP, calcium ions) amplify and relay the signal.

    Protein Phosphorylation

    • Protein kinases add phosphates to proteins for activation or inactivation, often creating cascades.
    • Protein phosphatases remove the phosphates. This acts as a molecular on/off switch.
    • This is common in nearly all signaling pathways

    Second Messenger cAMP

    • GPCR activation leads to adenylyl cyclase activation
    • Adenylyl cyclase converts ATP to cAMP
    • Cyclic AMP activates protein kinase A signaling pathway.

    Second Messenger Ca2+

    • Cytoplasmic Ca2+ concentration is lower than outside.
    • Increased Ca2+ can cause muscle contraction, substance secretion, and cell division.

    Signal Response

    • Signal transduction pathways regulate cellular activities
    • Cytoplasmic responses (enzyme activation, ion channel opening)
    • Nuclear responses (protein synthesis, gene expression changes in the nucleus)

    Signal Termination

    • Deactivation mechanisms are essential for cell signaling.
    • Molecular changes must be short-lived for cell alertness
    • Inactivation prevents signalling pathway components from permanently locking in one state preventing proper cell function.

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