Cell Cycle and Regulation
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Questions and Answers

What is the main event occurring during the S-phase of the cell cycle?

  • Cellular growth
  • Nuclear division
  • Cytoplasmic division
  • DNA replication (correct)

Mitosis consists of interphase and G0 phase.

False (B)

What are the two main stages of the cell cycle?

Interphase and Mitotic phase

During the _____ phase, chromatin condenses into chromosomes.

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

Match the following phases with their descriptions:

<p>G1-phase = Cellular growth and enzyme synthesis S-phase = DNA replication occurs G2-phase = Preparation for mitosis Telophase = Daughter chromosomes are at the poles</p> Signup and view all the answers

What characterizes the G1-phase of interphase?

<p>High rate of biosynthetic activities (C)</p> Signup and view all the answers

Cytokinesis happens during the G2 phase.

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

What is the purpose of the G2-phase?

<p>Rapid control of replicated DNA and preparation for division</p> Signup and view all the answers

What is the primary role of the Ink family of proteins?

<p>To halt the cell cycle in the G1 phase (B)</p> Signup and view all the answers

The Rb gene, when mutated, can lead to retinal cancer by allowing uncontrolled cell advancement through the G1 phase.

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

What is the role of the p53 gene in the regulation of the cell cycle?

<p>It prevents the propagation of genetically damaged cells.</p> Signup and view all the answers

The active form of Rb is ____ phosphorylated and inhibits E2F-dependent gene activation.

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

Match the following proteins with their corresponding functions:

<p>p21 = Holds the cell cycle at G1/S phase E2F = Stimulates entry into S phase p53 = Triggers apoptosis in irreparable DNA damage Rb = Inhibits G1/S phase progression</p> Signup and view all the answers

What primarily activates cyclin dependent kinases (CDKs)?

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

CDK activity varies throughout the cell cycle while CDK levels remain constant.

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

What is the role of Maturation Promoting Factor (MPF) in the cell cycle?

<p>MPF promotes passage to M phase and initiates nuclear division during mitosis.</p> Signup and view all the answers

The cyclin that helps cells commit to DNA replication at the end of G1 phase is _____

<p>Cyclin E</p> Signup and view all the answers

Match the cyclin class with their function:

<p>G1 cyclin = Helps cells pass the checkpoint in late G1 phase S cyclin = Initiates DNA synthesis M cyclins = Facilitates passage to M phase G1/S cyclin = Commits cells to DNA replication</p> Signup and view all the answers

Which of the following proteins are considered negative regulators of the cell cycle?

<p>CIP/KIP family (A)</p> Signup and view all the answers

Tumor suppressor proteins act as positive regulators of the cell cycle.

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

Cyclin D-CDK4 and Cyclin D-CDK6 are involved in the _____ phase of the cell cycle.

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

What is the main purpose of cytokinesis?

<p>To divide the cytoplasm and form two daughter cells (B)</p> Signup and view all the answers

The G0 phase is a stage where cells actively divide.

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

Name the three main checkpoints in the cell cycle.

<p>G1 checkpoint, G2 checkpoint, M checkpoint</p> Signup and view all the answers

Cyclin Dependent Kinases (Cdks) partner with cyclins to form a ______ protein kinase.

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

Which of the following is a characteristic of tumor suppressor proteins?

<p>They inhibit positive regulators. (C)</p> Signup and view all the answers

Match the following terms with their descriptions:

<p>G1 cyclins = Regulate the transition from G1 to S phase S cyclins = Are active during DNA synthesis M cyclins = Peak at the transition from G2 to M phase P53 proteins = Act as tumor suppressors</p> Signup and view all the answers

Cells can exit the cell cycle to enter the ______ phase, which is a non-dividing state.

<p>G0</p> Signup and view all the answers

What do positive regulators like cyclins do in the cell cycle?

<p>They control the changes necessary for cell division.</p> Signup and view all the answers

Flashcards

Cell Cycle

A series of events in eukaryotic cells leading to their replication.

Interphase

The stage of the cell cycle before mitosis, with cellular growth, nutrient accumulation, and DNA replication.

G1 phase

The first phase of interphase, characterized by cellular growth and synthesis of enzymes for DNA replication.

S phase

The phase where DNA replication occurs, creating identical sister chromatids.

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G2 phase

The phase in interphase between DNA replication and mitosis, where the cell checks and prepares for division.

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Mitosis

The phase of the cell cycle where the cell divides its nucleus (karyokinesis) and then its cytoplasm (cytokinesis).

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Prophase

The first stage of mitosis, where the nucleolus fades and chromosomes condense.

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Prometaphase

Stage of mitosis where the nuclear envelope breaks down.

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Metaphase

Stage of mitosis where chromosomes line up at the metaphase plate.

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Anaphase

Stage of mitosis where sister chromatids separate and move to opposite poles.

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Telophase

Stage of mitosis where daughter chromosomes reach the poles, and the spindle fibers disappear.

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Karyokinesis

The division of the nucleus during mitosis.

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Cytokinesis

The division of the cytoplasm during mitosis, resulting in two daughter cells.

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Cytokinesis

The division of the cytoplasm during cell division, creating two daughter cells with identical genetic information.

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G0 phase

A non-dividing state of a cell, often associated with a variable level of differentiation.

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Meiosis

A type of cell division that reduces the chromosome number by half, important for genetic variation.

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Cell Cycle Checkpoints

Stages in the cell cycle where the cell assesses internal and external conditions before proceeding.

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G1 checkpoint

Checks the integrity of DNA before DNA replication.

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G2 checkpoint

Ensures complete DNA replication before mitosis.

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M checkpoint

Monitors chromosome attachment to spindle fibers.

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Cell Cycle Regulators

Proteins that monitor and control the cell cycle progression.

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Positive Regulators

Proteins that promote cell division.

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Cyclins

Proteins that activate cyclin-dependent kinases (CDKs).

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Cyclin-Dependent Kinases (CDKs)

Enzymes that drive cell cycle events when partnered with cyclins.

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Negative Regulators

Proteins that inhibit cell cycle progression.

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Tumor Suppressor Proteins

Proteins that prevent uncontrolled cell growth.

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Cyclin-dependent kinases (CDKs)

A family of protein kinases that regulate the cell cycle by activating or deactivating target proteins through phosphorylation.

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Ink Family

A family of proteins that bind and inhibit CDK4/CDK6, halting the cell cycle in the G1 phase.

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CDK activation

CDKs are inactive alone; binding of cyclins causes activation, making them functional enzymes.

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CDK2-cyclin E/A

A combination of cyclin-dependent kinases and cyclins that usually drive cell cycle progression after G1.

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Rb gene

A tumor suppressor gene that controls cell cycle progression from G1 to S phase.

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Cyclin

Proteins that bind to and activate CDKs during specific phases of the cell cycle, regulating activity.

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Phosphorylation

Adding a phosphate group to a protein, changing its activity (activation or deactivation).

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pRb (hypophosphorylated)

The inactive form of the Rb protein, bound to E2F and preventing cell cycle advancement.

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pRb (hyperphosphorylated)

The active form of the Rb protein that is no longer bound to E2F, allowing cell cycle progression.

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G1 cyclin

Helps cells pass the late G1 checkpoint to commit to cell cycle progression.

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G1/S cyclin

Helps cells commit to DNA replication and enter S phase.

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p53

A tumor suppressor protein, activated by DNA damage or other signals, controlling cell cycle arrest, repair, senescence or apoptosis.

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p21

A protein produced by CKI gene and triggered by p53 to halt growth cycle at G1/S. Allowing time for DNA repair and allowing cell growth and DNA repair to occur

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S cyclin

Necessary for DNA synthesis at the start of S phase

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M cyclin

Initiates mitosis and nuclear division (including nuclear envelope breakdown).

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Maturation Promoting Factor (MPF)

A cyclin-CDK complex crucial for regulating mitosis.

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APC/C

Protein complex that triggers the destruction of proteins that hold chromosomes together.

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CDK inhibitors

Proteins that regulate CDK activity and prevent inappropriate cell cycle progression.

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CIP/KIP

Family of CDK inhibitors that help regulate the cell cycle.

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Study Notes

Cell Cycle and Regulation

  • Eukaryotic cells replicate through a series of events called the cell cycle
  • The cell cycle is broadly divided into two stages: Interphase and the Mitotic phase
  • Interphase (I) stage is characterized by cellular growth, accumulation of nutrients needed for mitosis, and DNA replication
  • Mitotic (M) phase is where the cell divides into two daughter cells
  • Interphase includes four phases: G1, S, G2, and G0
  • G1 phase: the first phase in interphase, located between mitosis and S phase, characterized by variable duration, high biosynthetic activity and synthesis of enzymes for DNA replication
  • S phase: DNA replication occurs, producing two genetically identical sister chromatids held together by a centromere
  • G2 phase: period between S phase and mitosis, associated with rapid DNA control and preparation for division
  • Mitosis phase is relatively brief, comprising nuclear division (karyokinesis) and cytoplasmic division (cytokinesis)
    • Prophase: nucleolus fades, chromatin condenses into chromosomes
    • Prometaphase: breakdown of the nuclear envelope
    • Metaphase: alignment of chromosomes at the metaphase plate
    • Anaphase: daughter chromosomes are pulled apart and move to the cell poles
    • Telophase: daughter chromosomes at poles, spindle fibers disappear, cytoplasm divides to form two daughter cells with identical genetic information
  • Exit phases:
    • G0 phase: non-dividing (rest) state, associated with variable levels of differentiation (e.g., muscle and nerve cells).
    • Meiosis: In germinal cells, it replaces mitosis and introduces genetic variation.
  • Cell Cycle Checkpoints:
    • G1 checkpoint: verifies the integrity of DNA before proceeding to S phase and DNA replication
    • G2 checkpoint: verifies completeness of genomic DNA replication before mitosis
    • M (Metaphase) checkpoint: monitors chromosome attachment to the mitotic spindle before anaphase and chromosomal segregation

Cell Cycle Regulators

  • Regulatory proteins monitor and dictate cell progression through stages
  • Positive regulators: control changes necessary for cell division
    • Cyclins: G1, G1/S, S, and M cyclins, associated with specific phases
    • Cyclin-Dependent Kinases (Cdks): enzymes that partner with cyclins
  • Negative regulators: control positive regulators, include:
    • Tumor suppressor proteins: Rb proteins and P53 proteins
    • Inhibitors of Cdks (CDKIs): two types - Ink and CIP families.
  • Specific examples of regulators are discussed, including the role of Rb and P53

Rb Gene

  • Rb gene regulates cells' advancement from G1/S phase
  • pRb arrests the cell cycle at G1 phase
  • Mutated Rb gene leads to uncontrolled cell growth, potentially causing cancer (e.g., retinoblastoma)
  • Rb regulation: active form is hypo-phosphorylated, activates E2F proteins to promote genes for S phase; in active cycling cells, Rb progressively become hyperphosphorylated, E2F binds DNA, activating genes important for S phase

p53 Gene

  • p53 gene acts as a guardian, preventing the proliferation of damaged/genetically altered cells
  • Can be activated by hypoxia, inappropriate oncogene signaling or DNA damage
  • Activated p53 controls cell cycle arrest, DNA repair, cellular senescence, and apoptosis
  • Activated p53 stimulates CKI gene, which produces p21 proteins to hold the cell cycle at G1/S phase, allowing DNA repair. If damage is irreparable, triggers apoptosis.

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Related Documents

Cell Cycle and its Regulation PDF

Description

Explore the essential stages of the cell cycle, which includes interphase and the mitotic phase. This quiz covers key concepts such as G1, S, G2 phases, and the processes of mitosis and cytokinesis. Test your knowledge on the events that lead to successful cell replication.

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