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?

They dictate the direction of cell movement. Signup and view all the answers

What role do integrins play in cell migration?

They mediate attachment to the extracellular matrix. Signup and view all the answers

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

Formation of lamellipodia. Signup and view all the answers

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

Wound healing Signup and view all the answers

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

Rac Signup and view all the answers

What is one primary event of chemotaxis in cells?

Movement towards a chemoattractant gradient Signup and view all the answers

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

They encode for proteins essential for cell cycle control. Signup and view all the answers

What distinguishes temperature-sensitive cdc mutants from normal yeasts?

Their proteins function properly at low temperatures. Signup and view all the answers

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

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

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

It arrests in anaphase unable to exit mitosis. Signup and view all the answers

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

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

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

Synthesis Signup and view all the answers

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

G2 phase Signup and view all the answers

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

Mitosis Signup and view all the answers

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

To monitor environmental conditions and prepare for division Signup and view all the answers

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

Environmental conditions must be checked and appropriate stimuli identified Signup and view all the answers

During which phase does the majority of DNA replication occur?

S phase Signup and view all the answers

What is the purpose of the cell cycle control system?

To regulate transitions between different phases of the cell cycle Signup and view all the answers

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

S phase takes longer than M phase Signup and view all the answers

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

A washing machine Signup and view all the answers

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

To divide the cytoplasm and complete cell division Signup and view all the answers

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

To promote the formation of branched cortical actin. Signup and view all the answers

Which process is regulated by Rho-GTP?

Formation of contractile actin stress fibers. Signup and view all the answers

How do small GTPases like Rac become activated?

Through nucleotide exchange facilitated by GEF. Signup and view all the answers

What triggers the hydrolysis of GTP in small GTPases?

The termination of signal transduction. Signup and view all the answers

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

They activate regulators such as GEF. Signup and view all the answers

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

Rho-GDP. Signup and view all the answers

Which of the following statements about GEF is true?

GEF facilitates the exchange of GDP to GTP. Signup and view all the answers

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

It checks if the environment is favorable and if DNA is intact. Signup and view all the answers

What happens at the G2 checkpoint?

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

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

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

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

Cells may pause and repair DNA damage before continuing. Signup and view all the answers

What characterizes the G0 state of a cell?

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

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

Metaphase checkpoint Signup and view all the answers

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

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

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

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

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

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

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

G1 phase 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.