Cell Division and Mitosis Quiz
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Questions and Answers

What is the primary role of the mitotic checkpoint?

  • To activate the anaphase-promoting complex
  • To promote the destruction of Cohesins
  • To complete mitosis regardless of chromosome attachment
  • To ensure all chromosomes are attached to the mitotic spindle (correct)

What effect does Mad2 binding have during cell division?

  • Promotes the cleavage of Cohesins
  • Delays the metaphase-anaphase transition (correct)
  • Inhibits the destruction of Securin
  • Increases the activity of Cdc20-APC

Which protein's destruction is triggered by the activated anaphase-promoting complex (APC)?

  • Separase
  • Mad2
  • Securin (correct)
  • Cohesin

What happens if the mitotic checkpoint is activated for an extended period?

<p>It leads to cell death (C)</p> Signup and view all the answers

How does Separase contribute to the separation of sister chromatids?

<p>By cleaving the Cohesin complexes (D)</p> Signup and view all the answers

What is one of the main functions of cell division?

<p>Reproduction of cells (A)</p> Signup and view all the answers

During which phase of the cell cycle does DNA replication occur?

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

Which checkpoint in the cell cycle is considered the primary decision point for many cells?

<p>G1 checkpoint (A)</p> Signup and view all the answers

What marks the beginning of cytokinesis?

<p>Cleavage furrow formation (D)</p> Signup and view all the answers

What is the consequence if a cell does not receive a go-ahead signal at the G1 checkpoint?

<p>The cell enters the G0 nondividing state. (C)</p> Signup and view all the answers

What happens during prophase?

<p>Chromatin fibers become tightly coiled (D)</p> Signup and view all the answers

Which type of cells is most likely to divide frequently throughout life?

<p>Skin cells (A)</p> Signup and view all the answers

Which stage of mitosis involves the alignment of chromosomes at the cell's equator?

<p>Metaphase (B)</p> Signup and view all the answers

What role do external factors play in the regulation of cell division?

<p>They include signals from outside the cell. (C)</p> Signup and view all the answers

What is a key role of the mitotic spindle during cell division?

<p>Attach to kinetochores (B)</p> Signup and view all the answers

At which phases do the major checkpoints in the cell cycle occur?

<p>G1, G2, M (A)</p> Signup and view all the answers

Which phase of the cell cycle occurs after the S phase?

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

What happens during anaphase of mitosis?

<p>Sister chromatids separate (B)</p> Signup and view all the answers

What could be a potential internal signal that influences the G1 checkpoint decision?

<p>Cell size (B)</p> Signup and view all the answers

Which of the following best describes the G0 phase of the cell cycle?

<p>A nondividing state. (B)</p> Signup and view all the answers

What is a key characteristic of mature nerve and muscle cells in relation to cell division?

<p>They do not appear to divide at all after maturity. (A)</p> Signup and view all the answers

What is required for the activity of Cdk?

<p>Phosphorylation at a specific site (B)</p> Signup and view all the answers

How are cyclins regulated in terms of their abundance?

<p>Through protein degradation via ubiquitylation (C)</p> Signup and view all the answers

What role does activated p53 protein play in the cell cycle?

<p>Stimulates transcription of the p21 gene (C)</p> Signup and view all the answers

What triggers the activation of protein phosphatase in the Cdk complex?

<p>Removal of all inhibitory phosphate groups (D)</p> Signup and view all the answers

What can a cell decide at the G1 checkpoint?

<p>Commit to dividing into two (C), Pause until conditions are favorable (D)</p> Signup and view all the answers

Which of the following statements about Cdk inhibitor proteins is correct?

<p>They can respond to DNA damage. (A)</p> Signup and view all the answers

What is the function of maturation promoting factor (MPF) in the cell cycle?

<p>Triggers M phase by phosphorylating various proteins (B)</p> Signup and view all the answers

What happens to cyclins after they execute their function in the cell cycle?

<p>They are targeted for destruction through ubiquitylation. (B)</p> Signup and view all the answers

What initiates the activation of M-Cdk at the end of G2?

<p>Dephosphorylation by Cdc25 (C)</p> Signup and view all the answers

Which site modification is essential for M-Cdk to become active?

<p>Both phosphorylation and dephosphorylation (C)</p> Signup and view all the answers

What is the role of Cdc25 in the activation of M-Cdk?

<p>It removes inhibitory phosphates from M-Cdk. (C)</p> Signup and view all the answers

How does M-Cdk promote its own further activation?

<p>Through a positive feedback loop (B)</p> Signup and view all the answers

What is the main function of the spindle-attachment checkpoint?

<p>To block sister chromatid separation if kinetochores are improperly attached (C)</p> Signup and view all the answers

What action does activated M-Cdk take against the inhibitory kinase Wee1?

<p>It directly inhibits the activity of Wee1. (D)</p> Signup and view all the answers

Which proteins are recruited to unattached kinetochores during improper attachment?

<p>Mad2 (B)</p> Signup and view all the answers

What is the role of the SCF complex in cell cycle regulation?

<p>To target specific cyclins and some CKIs for degradation (C)</p> Signup and view all the answers

What is required for the activation of cyclin-dependent kinases (Cdks)?

<p>Binding of cyclins (C)</p> Signup and view all the answers

Which type of cyclin assists in promoting passage through the restriction point in late G1 phase?

<p>G1-cyclins (D)</p> Signup and view all the answers

How do cyclin levels change throughout the cell cycle?

<p>They are low during interphase and peak during mitosis. (D)</p> Signup and view all the answers

What is NOT a mechanism of regulation for the cyclin-Cdk complex?

<p>Cdk binding to DNA (A)</p> Signup and view all the answers

What is necessary for a Cdk to be fully active?

<p>Phosphorylation at one site and dephosphorylation at two sites (A)</p> Signup and view all the answers

Which class of cyclins binds to Cdks during S phase and is required for initiating DNA replication?

<p>S-cyclins (C)</p> Signup and view all the answers

What event triggers the entry into M phase?

<p>Increased levels of M-cyclins (D)</p> Signup and view all the answers

Which statement is incorrect regarding the cyclin-Cdk complex?

<p>It is always active during the cell cycle. (B)</p> Signup and view all the answers

Flashcards

Cell division

The process by which a cell reproduces, involving an orderly sequence of events where the cell duplicates its contents and divides into two daughter cells.

Mitosis

The phase of the cell cycle where the nucleus divides, resulting in two daughter nuclei.

Cytokinesis

The phase of the cell cycle where the cytoplasm divides, resulting in two daughter cells.

Interphase

The phase of the cell cycle where the cell grows and prepares for DNA replication. It includes G1, S, and G2 phases.

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G1 phase

The first phase of interphase, where the cell grows and carries out normal metabolic functions.

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S phase

The second phase of interphase, where the cell replicates its DNA.

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G2 phase

The third phase of interphase, where the cell grows and prepares for mitosis.

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Prophase

The first stage of mitosis, where the chromatin condenses into visible chromosomes, the nucleolus disappears, and the mitotic spindle begins to form.

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Cell division frequency

The rate at which cells divide varies depending on the cell type. Some cells divide frequently throughout life, while others have the potential to divide but remain in reserve. Highly specialized cells like nerve and muscle cells typically do not divide after maturity.

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Cell cycle control system

The cell cycle control system is a complex system of proteins and signaling pathways that regulates the progression of the cell cycle. It ensures that the cell cycle occurs in a precise and ordered sequence.

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Checkpoints in the cell cycle

Checkpoints are critical control points in the cell cycle where the cell evaluates conditions and decides whether to proceed or stop the cell cycle.

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G1 checkpoint

The G1 checkpoint, also known as the restriction point, is a key decision point where a cell assesses its readiness to proceed through the cell cycle. If conditions are favorable, the cell receives a go-ahead signal and continues. If not, it exits the cell cycle and enters a non-dividing state called G0.

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Go-ahead signal at the G1 checkpoint

If a cell receives a go-ahead signal at the G1 checkpoint, it will continue through the cell cycle. This signal is influenced by both internal factors like cell size and nutrient availability, as well as external factors like growth factors.

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External factors in cell division

External factors are signals or conditions from the outside of the cell that influence whether or not a cell will divide. Examples include growth factors, nutrients, and signals from neighboring cells.

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Internal factors in cell division

Internal factors are signals or conditions originating within the cell that influence its decision to divide. These factors include cell size, nutrient availability, DNA integrity, and the presence of specific proteins.

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Cyclin-Cdk complex

A protein complex crucial for cell cycle progression. It consists of a Cyclin protein and a Cdk (Cyclin-Dependent Kinase) protein.

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Cyclins

A type of protein that helps regulate the cell cycle by binding to and activating Cdk proteins. Their levels fluctuate throughout the cell cycle.

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Cyclin-Dependent Kinases (Cdks)

A family of protein kinases that are activated by cyclins. They control the progression of the cell cycle by phosphorylating specific target proteins.

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Ubiquitylation

A process where a protein is tagged with a small protein called ubiquitin, marking it for degradation. This is often used to regulate the abundance of cyclins in the cell cycle.

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Maturation Promoting Factor (MPF)

A protein complex that promotes the transition from G2 to M phase. It phosphorylates target proteins that are involved in initiating mitosis.

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Cdk Inhibitors

Proteins that inhibit the activity of Cdk proteins. They help control cell cycle progression by pausing the cycle if conditions are unfavorable.

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p53

A protein involved in the DNA damage response. When DNA is damaged, p53 is activated, which then triggers the production of a Cdk inhibitor called p21.

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What are Cyclin-Dependent Kinases (Cdks)?

Cyclin-dependent kinases (Cdks) are enzymes that control the cell cycle. They are inactive unless bound to a cyclin protein.

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What are Cyclins?

Cyclins are proteins that regulate the activity of Cdks. They bind to Cdks and activate them, triggering specific events in the cell cycle.

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How do Cyclins and Cdks work together?

Cyclin-Cdk complexes are formed when a cyclin binds to a Cdk. These complexes are essential for controlling the progression of the cell cycle.

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What are the different types of Cyclins?

There are four main classes of cyclins: G1-cyclins, G1/S-cyclins, S-cyclins, and M-cyclins. Each class is responsible for promoting a specific event in the cell cycle.

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How are Cdks activated?

The activation of Cdk requires phosphorylation by a Cdk-activating kinase (CAK), along with binding to a cyclin. This ensures that Cdk only triggers specific events when needed.

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How is the activity of Cdk regulated?

Cdk activity is regulated through multiple mechanisms, including post-translational modifications, transcriptional regulation, Cdk inhibitors, and cyclical proteolysis. This ensures precise control of the cell cycle.

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How do cyclin levels change during the cell cycle?

The concentration of cyclins rises and falls during the cell cycle. This fluctuation is crucial for regulating Cdk activity and driving the cell through different phases.

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How is the Cyclin-Cdk complex regulated?

The cyclin-Cdk complex is regulated by phosphorylation, dephosphorylation, and binding to cyclin inhibitors. This ensures that Cdk activity is only activated when necessary.

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Spindle Assembly Checkpoint

A checkpoint that monitors whether all chromosomes are correctly attached to the mitotic spindle before allowing the cell to progress to anaphase.

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Anaphase-Promoting Complex (APC)

A protein complex that promotes the separation of sister chromatids during anaphase. It does this by targeting proteins for ubiquitylation and degradation.

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Securin

A protein that inhibits the activity of Separase, preventing premature separation of sister chromatids.

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Separase

An enzyme that cleaves the cohesin proteins that hold sister chromatids together, allowing them to separate during anaphase.

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Cohesins

Proteins that hold sister chromatids together during mitosis. They are cleaved by Separase to allow chromosome segregation.

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M-Cdk

A protein kinase complex composed of M cyclin and a catalytic subunit called Cdk, which promotes entry into mitosis (M phase).

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Cdc25

A protein phosphatase that activates M-Cdk by removing inhibitory phosphates. It's like a key that unlocks M-Cdk's activity.

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Wee1

An enzyme that inhibits M-Cdk by adding inhibitory phosphates. It acts as a "brake" on M-Cdk activity.

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Positive feedback loop in M-Cdk activation

A positive feedback loop where activated M-Cdk further activates more M-Cdk, leading to a rapid increase in M-Cdk activity. It's like a chain reaction!

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Kinetochore

A specialized region on a chromosome where microtubules of the spindle attach during cell division.

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Spindle-attachment checkpoint

A checkpoint that ensures all chromosomes are properly attached to the spindle before sister chromatids separate, preventing errors in cell division.

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CKI (Cdk inhibitor protein)

A protein that inhibits cell cycle progression by binding to and blocking the activity of cyclin-dependent kinases (Cdks).

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SCF complex

A ubiquitin ligase complex that targets G1/S cyclins and some CKIs for degradation, promoting the transition from the G1 to the S phase of the cell cycle.

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Study Notes

Cell Cycle Overview

  • The cell cycle is a series of events that leads to cell division
  • Cell division is crucial for reproduction, growth, and tissue repair
  • Cells duplicate their genetic material before dividing to ensure each daughter cell receives an exact copy
  • The cell cycle is regulated by checkpoints which help prevent errors and allow time for accurate duplication

Learning Outcomes

  • Describe the overall purposes of cell division
  • Describe the structural organization of a eukaryotic genome
  • Explain cytokinesis
  • List the phases of the cell cycle and describe the events in each phase
  • Describe the roles of checkpoints, cyclin, Cdks, and MPF in the cell cycle control system
  • Describe internal and external factors influencing the cell cycle control
  • Explain how abnormal cell division of cancerous cells escapes normal cell cycle control

Functions of Cell Division

  • Reproduction (example: bacteria, amoeba)
  • Growth and development (example: embryos)
  • Tissue renewal (example: skin, blood)

The Cell Cycle

  • The cell division process is a part of the cell cycle
  • A cell duplicates its contents and divids into two
  • Each new cell receives a copy of the genetic material (DNA)
  • Cells duplicate their genetic material before division

Phases of the Cell Cycle

  • Mitotic Phase:
    • Mitosis: division of the nucleus
    • Cytokinesis: division of the cytoplasm
  • Interphase:
    • G1 phase: cell growth and preparation for DNA synthesis
    • S phase: DNA replication
    • G2 phase: preparation for mitosis

Stages of Mitotic Cell Division

  • Prophase: chromatin fibers coil, nucleoli disappear, centrosomes move apart, mitotic spindle forms
  • Prometaphase: nuclear envelope fragments, microtubules interact with chromosomes, kinetochores attach to microtubules
  • Metaphase: centrosomes at opposite poles, chromosomes align at the metaphase plate, kinetochores of sister chromatids attach to microtubules
  • Anaphase: paired centromeres separate, sister chromatids move to opposite poles
  • Telophase: daughter nuclei form, chromatin fibers decondense, cytokinesis occurs

Cytokinesis

  • Cytoplasm divides; resulting in two daughter cells
  • In animal cells, characterized by a cleavage furrow
  • In plant cells, characterized by a cell plate

Interphase

  • G1 Phase: Post-mitotic phase. Cell growth and accumulation of energy
  • S Phase: Synthesis phase. DNA and centriole replication
  • G2 Phase: Pre-mitotic gap phase. Synthesis of RNA and proteins

The Cell Cycle Control System

  • Cell cycle events are directed by a cell-cycle control system
  • Checkpoints are critical control points in the cell cycle
    • Checkpoints in G1, G2, and M phases
    • Control cell cycle progression through chemical signals
  • Checkpoints monitor cell size, DNA replication, chromosome attachment errors and nutrients in the exterior environment

The G1 Checkpoint

  • Major decision point
  • If the cell has a go-ahead signal, it continues through the cell cycle
    • Internal signals: cell size, nutrition signals for metabolism
    • External signals: growth factors
  • If the cell does not receive a go-ahead signal, it may halt or enter a nondividing state (G0)

External Signals

  • Factors/signals outside of cell affecting the division process
  • Chemical factors: nutrients, presence of growth factors
  • Physical factors: density-dependent inhibition (cells stop dividing when crowded), anchorage dependence (cells need a surface to divide)
  • Anchorage to substrate controlled by membrane protein-cytoskeleton interactions

Growth Factors

  • Proteins that stimulate division in other cells
  • Bind to receptors that trigger cell growth
  • Cells usually respond to a combination of growth factors

Internal Factors

  • Kinases: enzymes that transfer phosphate groups to molecules
  • Cyclins: proteins that activate kinases
  • Control cell cycle progression

Maturation Promoting Factor (MPF)

  • Triggers entry into M phase
  • Oscillates during the cell cycle in Xenopus embryos

G2 Checkpoint

  • Ensures all DNA replicated and any errors are fixed

Checkpoint: Spindle Assembly

  • Mitosis only completes when all chromosomes are attached to the mitotic spindle
  • Delaying anaphase prevents chromosome segregation errors

The APC

  • Triggers separation of sister chromatids by promoting the destruction of cohesins
  • Holds sister chromatids together in the replicated chromosome
  • Cleaves cohesin complexes, allowing movement of chromosomes to opposite poles

DNA Damage Arresting the Cell Cycle in G1

  • DNA damage initiates a response that halts the cell cycle
  • Activates p53, which leads to the production of p21
  • p21 inhibits kinases associated with cell cycle progression causing arrest in G1

Regulation of Cyclin-Cdk Complexes

  • Cyclin levels alter based on cell phase, activating or deactivating kinases
  • Phosphorylation (adding phosphate groups) and dephosphorylation (removing phosphate groups) impact the activity of cyclin-dependent kinases (Cdks)
  • Ubiquitination and subsequent degradation regulates abundance of cyclins

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The Cell Cycle PDF

Description

Test your knowledge about the cell division process, focusing on the mitotic checkpoint, roles of key proteins, and various phases of mitosis. This quiz covers essential concepts in cell cycle regulation and the implications of checkpoints on cell division. Perfect for biology students at any level.

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