Retta L.10
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Questions and Answers

Which small GTPase is primarily responsible for promoting the formation of filopodia?

  • Rac
  • GAP
  • cdc42 (correct)
  • Rho
  • What is the primary function of Rac in cell migration?

  • Activation of myosin
  • Promotion of lamellipodia (correct)
  • Formation of stress fibers
  • Inhibition of cdc42
  • Which extracellular signal is associated with the activation of the small GTPase Rho?

  • Insulin
  • Lysophosphatidic acid (correct)
  • Platelet-Derived Growth Factor (PDGF)
  • Bradykinin
  • How do external signals influence cell migration?

    <p>They dictate the direction of cell movement.</p> Signup and view all the answers

    What role do integrins play in cell migration?

    <p>They mediate attachment to the extracellular matrix.</p> Signup and view all the answers

    What is the consequence of Rac dominating at the leading edge of a migrating cell?

    <p>Formation of lamellipodia.</p> Signup and view all the answers

    Which of the following is a physiological example of cell migration?

    <p>Wound healing</p> Signup and view all the answers

    During collective cell migration, which GTPase is emphasized for its role in polarization?

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

    What is one primary event of chemotaxis in cells?

    <p>Movement towards a chemoattractant gradient</p> Signup and view all the answers

    What is the primary role of cdc genes in the cell cycle?

    <p>They encode for proteins essential for cell cycle control.</p> Signup and view all the answers

    What distinguishes temperature-sensitive cdc mutants from normal yeasts?

    <p>Their proteins function properly at low temperatures.</p> Signup and view all the answers

    In experiments with oocytes from Xenopus, what was concluded about maturation promoting factors (MPF)?

    <p>MPF promotes mitosis when cytoplasm from M phase cells is injected.</p> Signup and view all the answers

    What characterizes the cdc15 mutant in budding yeast at high temperatures?

    <p>It arrests in anaphase unable to exit mitosis.</p> Signup and view all the answers

    Why are mammalian cells considered less efficient for studying the cell cycle compared to yeast?

    <p>They need 24 hours to complete a division cycle.</p> Signup and view all the answers

    What does the 'S' in S phase stand for in the context of the cell cycle?

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

    Which phase directly follows the S phase in the cell cycle?

    <p>G2 phase</p> Signup and view all the answers

    Which type of cell division is primarily associated with the M phase?

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

    What is the primary role of the gap phases (G1 and G2) in the cell cycle?

    <p>To monitor environmental conditions and prepare for division</p> Signup and view all the answers

    What must occur before a cell can progress from G1 phase to S phase?

    <p>Environmental conditions must be checked and appropriate stimuli identified</p> Signup and view all the answers

    During which phase does the majority of DNA replication occur?

    <p>S phase</p> Signup and view all the answers

    What is the purpose of the cell cycle control system?

    <p>To regulate transitions between different phases of the cell cycle</p> Signup and view all the answers

    How do the S and M phases differ in terms of duration?

    <p>S phase takes longer than M phase</p> Signup and view all the answers

    What analogy is used to explain the cell-cycle control system?

    <p>A washing machine</p> Signup and view all the answers

    What is the main function of cytokinesis in the cell cycle?

    <p>To divide the cytoplasm and complete cell division</p> Signup and view all the answers

    What is the primary function of Rac-GTP in cell migration?

    <p>To promote the formation of branched cortical actin.</p> Signup and view all the answers

    Which process is regulated by Rho-GTP?

    <p>Formation of contractile actin stress fibers.</p> Signup and view all the answers

    How do small GTPases like Rac become activated?

    <p>Through nucleotide exchange facilitated by GEF.</p> Signup and view all the answers

    What triggers the hydrolysis of GTP in small GTPases?

    <p>The termination of signal transduction.</p> Signup and view all the answers

    What role do cell surface receptors play in the activation of Rho-GTPase?

    <p>They activate regulators such as GEF.</p> Signup and view all the answers

    What is the inactive state of Rho when it is not bound to GTP?

    <p>Rho-GDP.</p> Signup and view all the answers

    Which of the following statements about GEF is true?

    <p>GEF facilitates the exchange of GDP to GTP.</p> Signup and view all the answers

    What role does the G1 checkpoint play in the cell cycle?

    <p>It checks if the environment is favorable and if DNA is intact.</p> Signup and view all the answers

    What happens at the G2 checkpoint?

    <p>Cells verify that DNA is intact and fully replicated prior to M phase.</p> Signup and view all the answers

    Which of the following statements about the transition from G1 to S phase is true?

    <p>After passing the restriction point, cells become committed to DNA replication.</p> Signup and view all the answers

    How do cells respond to DNA damage during the cell cycle?

    <p>Cells may pause and repair DNA damage before continuing.</p> Signup and view all the answers

    What characterizes the G0 state of a cell?

    <p>Cells exit the cell cycle and can remain for extended periods without dividing.</p> Signup and view all the answers

    Which checkpoint is responsible for confirming that all chromosomes are properly attached before anaphase?

    <p>Metaphase checkpoint</p> Signup and view all the answers

    Which statement best describes the function of mitotic signals (mitogens)?

    <p>They induce the onset of mitosis by informing cells it is time to divide.</p> Signup and view all the answers

    What is the significance of backup mechanisms in the cell cycle control system?

    <p>They provide remedies for repair and maintain cycle integrity under malfunction.</p> Signup and view all the answers

    During early embryonic development, how does cell division differ from later stages?

    <p>Cells divide without growing in size during early stages.</p> Signup and view all the answers

    Which cell cycle phase can exhibit variation in length depending on conditions and signaling?

    <p>G1 phase</p> Signup and view all the answers

    Study Notes

    Cell Polarization and Migration

    • Rho-GTPase proteins, including Rac-GTP and Rho-GTP, regulate cell migration and cytoskeletal structure formation.
    • Rac-GTP supports branched cortical actin for lamellipodia protrusions, while Rho-GTP promotes contractile actin stress fibers.
    • Rho-GTPase act as molecular switches, hydrolyzing GTP to GDP and enabling signal transduction when bound to GTP.
    • Activation of small GTPases happens through Guanine nucleotide Exchanging Factors (GEF), promoting GDP to GTP exchange, leading to a downstream signaling cascade.
    • Key Rho GTPases include cdc42 (filopodia formation), Rac (lamellipodia formation), and Rho (stress fiber formation).
    • Extracellular signals, like PDGF and LPA, activate the specific GTPases, influencing cytoskeletal dynamics crucial for cell protrusion and migration.
    • Cell migration is influenced by external signals directing movement, exemplified by Rac activation at the leading edge and Rho at the rear.

    Chemotaxis

    • Cell migration occurs in response to extracellular cues such as chemoattractants released by bacteria.
    • Cells exhibit polarized morphology, with leading edge protrusions and traction at the rear, facilitating directional movement.
    • Collective cell migration observed in epithelial cells occurs during processes like wound healing, requiring coordination among multiple cells.
    • Integrins mediate cell attachment to the extracellular matrix and interact with the actin-myosin cytoskeleton, supporting migration.

    Cell Cycle Overview

    • The cell cycle consists of four phases: G1, S, G2, and M phases, underpinning cell growth and division.
    • The S phase involves duplication of chromosomes (synthesis), while the M phase includes mitosis and cytokinesis (cell division).
    • G1 and G2 phases serve as checkpoints to assess environmental suitability for cell cycle progression.
    • Cell cycle regulation is crucial, ensuring DNA integrity and appropriate environmental conditions before moving into S or M phases.

    Cell Cycle Control System

    • Checkpoints in the cell cycle control system monitor internal and external conditions, allowing cells to transition safely between phases.
    • Critical control points exist before entering S (to check nutrient availability) and M phases (to ensure proper DNA replication).
    • G1 phase varies in length dependent on extracellular signals; unfavorable conditions may lead to cell entry into a resting state (G0).
    • Cells can withdraw from the cycle permanently upon differentiation or temporarily during G0 before re-entering.

    Critical Features for Cell Cycle Guidance

    • A timing mechanism ensures events like DNA replication occur at specific moments.
    • Events are initiated in the correct order, with binary switches triggering them irreversibly.
    • Backup mechanisms exist to address malfunctions, ensuring robustness in cell cycle progression.
    • Checkpoints assess environmental favorability and DNA integrity, influencing whether cells proceed, pause, or withdraw from the cycle.### Cell Cycle Progression and Regulation
    • Incomplete DNA replication during S or G2 phase inhibits cell cycle progression to subsequent phases.
    • Proper attachment of chromosomes to the mitotic spindle is crucial for cell cycle advancement during M phase.

    Experimental Models for Cell Cycle Study

    • Simple eukaryotes like yeast, which can divide by fission or budding, are key experimental models for cell cycle research.
    • Systematic searches for mutations in yeasts that affect essential cell-cycle control genes contributed significantly to discoveries.
    • Mutations in cdc genes (cell-cycle-division genes) impact cell cycle transitions.

    Temperature-Sensitive cdc Mutants

    • Temperature-sensitive cdc mutants function at low temperatures but malfunction at high temperatures due to improper protein folding.
    • High temperatures prevent transitions from G1 to S phase, allowing scientists to identify critical genes for cell cycle progression.
    • At permissive temperatures, cells divide normally, while restrictive temperatures hold cells at specific cycle stages.

    Characteristics of cdc Mutants

    • cdc15 mutant yeast cells complete anaphase but do not exit mitosis, leading to uniform arrest with enlarged buds typical of late M phase.
    • The cdc15 protein is essential for cytokinesis, demonstrating the mutation's impact on cell division.

    Xenopus Oocytes as a Model Organism

    • Xenopus oocytes are valuable for identifying factors that promote cell cycle progression due to their rapid cleavage post-fertilization (one division cycle every 30 minutes).
    • Maturation promoting factors (MPF) were discovered by injecting cytoplasm from M phase cells into oocytes, triggering mitosis, indicating their presence.

    Maturation Promoting Factors (MPF)

    • MPF is produced during mitosis but absent in interphase, suggesting new factors trigger mitosis.
    • Experiments showing how cytoplasm from frog eggs induces nuclei from frog sperm to enter mitosis further support MPF's role.

    Mammalian Cells in Cell Cycle Study

    • Mammalian cells have a longer division time (24 hours) than simpler organisms, requiring different monitoring approaches.
    • Molecular tools like 3H-thymidine and bromodeoxyuridine (BrdU) are used to label cells in the S phase.
    • Autoradiography visualizes 3H-thymidine incorporation, while immunofluorescent microscopy identifies cells that have replicated DNA using BrdU.

    Quantifying DNA Duplication

    • Flow cytometry can quantify cells undergoing DNA duplication by detecting fluorescent emissions from labeled dyes.
    • This quantitative analysis allows for precise measurement of the cell cycle's progression in mammalian cells.

    Importance of Cell Cycle Checkpoints

    • G1 checkpoint ensures the environment is suitable for S phase entry; G2 to M transition checkpoint confirms DNA replication completion.
    • M phase checkpoint guarantees all chromosomes are attached to the spindle.
    • DNA damage checkpoints delay G1 and G2 progression, allowing time for repair before resuming the cell cycle.

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    Description

    This quiz focuses on the Rho protein family and its role in cell polarization and migration. It covers the function of Rho-GTPase proteins and their impact on cytoskeletal structure formation through distinct regulatory pathways. Test your knowledge on how these proteins influence signal transduction in cell movements.

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