Cell Cycle Regulation Quiz
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Questions and Answers

What is the primary role of cyclins in cell cycle regulation?

  • To phosphorylate target proteins.
  • To inhibit the activity of Cdks.
  • To activate cyclin-dependent kinases (Cdk) by binding to them. (correct)
  • To regulate the availability of nucleotides.

Which of the following statements accurately describes cyclin-dependent kinases (Cdk)?

  • Cdks can function independently without cyclins.
  • Cdks regulate cell cycle events through the phosphorylation and dephosphorylation of target proteins. (correct)
  • Cdks are only active in the presence of cyclin A.
  • Cdks catalyze the degradation of cyclins to ensure cell cycle progression.

What is the main purpose of the G1 checkpoint in the cell cycle?

  • To ensure DNA replication occurs without error
  • To confirm that all chromosomes are correctly attached to the spindle
  • To facilitate the progression from metaphase to anaphase
  • To assess cell size, nutrient availability, growth factors, and DNA damage (correct)

Which of the following cyclins is involved in the regulation of the G2/M transition of the cell cycle?

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

Which checkpoint specifically monitors for successful DNA replication?

<p>G2 checkpoint (A)</p> Signup and view all the answers

What must occur for a cyclin-dependent kinase (Cdk) to become activated?

<p>It must bind to a cyclin. (D)</p> Signup and view all the answers

What does the M checkpoint primarily check for during cell division?

<p>Correct attachment of chromosomes to the spindle apparatus (D)</p> Signup and view all the answers

Which of the following is NOT a factor checked at the G2 checkpoint?

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

Which category of molecules do cyclins belong to in the context of cell cycle regulation?

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

In the context of internal control mechanisms, which phase lacks a checkpoint for assessing growth factors?

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

What is the primary role of retinoblastoma protein (Rb) in the cell cycle?

<p>It halts the cell cycle at the G1 checkpoint. (B)</p> Signup and view all the answers

Which of the following statements best describes the role of p53 in cellular function?

<p>It stimulates the activity of DNA repair enzymes when damage is detected. (A)</p> Signup and view all the answers

What is the common outcome for the regulatory proteins Rb, p53, and p21 in cancerous cells?

<p>They are damaged or non-functional, facilitating cell replication. (C)</p> Signup and view all the answers

At which checkpoint do Rb, p53, and p21 primarily exert their regulatory effects?

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

Which statement is true regarding the absence of p53 in cancer cells?

<p>It contributes to the inability of the cell to monitor DNA integrity. (D)</p> Signup and view all the answers

Which statement is true regarding the initiation of cell division?

<p>It can be triggered by external events such as nearby cell death. (B)</p> Signup and view all the answers

What effect does crowding of cells have on cell division?

<p>It can inhibit cell division by signaling density-dependent restriction. (D)</p> Signup and view all the answers

Which of the following is NOT a factor that triggers cell division?

<p>Internal cellular energy levels (A)</p> Signup and view all the answers

What role do checkpoints (G1, G2, and M) play in the cell cycle?

<p>They regulate the timing of events by assessing cell conditions. (B)</p> Signup and view all the answers

Which external event can potentially inhibit cell division?

<p>Death of a nearby cell (C)</p> Signup and view all the answers

What is the role of the Cdk2-cyclin A complex in late G1?

<p>It prevents the activation of E2F. (C)</p> Signup and view all the answers

What happens to the Rb protein during the cell cycle as it approaches late G1?

<p>It undergoes a shape change upon phosphorylation. (A)</p> Signup and view all the answers

Which protein complex is responsible for enabling the transition from G1 to S phase?

<p>Cdk2-cyclin A complex. (B)</p> Signup and view all the answers

During which phase is E2F promoted to transcribe genes necessary for DNA synthesis?

<p>Only in late G1 phase. (B)</p> Signup and view all the answers

How does the inactivity of Rb influence E2F during middle G1?

<p>Rb prevents E2F from activating genes. (B)</p> Signup and view all the answers

Which type of molecules are responsible for promoting the progression of the cell to the next phase?

<p>Cyclins and cyclin-dependent kinases (A)</p> Signup and view all the answers

What is the role of Cyclin-dependent kinase inhibitor 1 (p21) in the cell cycle?

<p>Halts the cell cycle (B)</p> Signup and view all the answers

Which of the following is NOT a positive regulator of the cell cycle?

<p>Retinoblastoma protein (A), Tumour protein p53 (D)</p> Signup and view all the answers

Which of the following proteins is classified as a tumour suppressor that stops the cell cycle?

<p>Tumour protein p53 (D)</p> Signup and view all the answers

What is the primary function of retinoblastoma protein (Rb) in the cell cycle?

<p>Halt the cell cycle (D)</p> Signup and view all the answers

What role do growth factors play in the cell cycle?

<p>They stimulate cell growth and can become oncogenes when mutated. (A)</p> Signup and view all the answers

Which statement accurately describes proto-oncogenes?

<p>They are normally present genes that promote cell growth when mutated. (B)</p> Signup and view all the answers

What is the primary function of tumor-suppressor genes?

<p>To inhibit cell division and prevent tumor growth. (A)</p> Signup and view all the answers

Which of the following accurately describes the effect of growth factors binding to their receptors?

<p>They activate signaling pathways that encourage cell proliferation and angiogenesis. (C)</p> Signup and view all the answers

Which factor is NOT involved in the intracellular signaling pathways triggered by growth factor binding?

<p>p53 (D)</p> Signup and view all the answers

What is the primary role of cyclin D in the cell cycle?

<p>Drives the G1 - S transition and commits the cell to DNA replication (A)</p> Signup and view all the answers

Which cyclin-CDK complex is primarily associated with the transition from G2 to M phase?

<p>Cyclin B - Cdk 1 (Cdc2) (A)</p> Signup and view all the answers

What is a characteristic function of cyclin E in the cell cycle?

<p>Initiates DNA replication in early S phase (C)</p> Signup and view all the answers

Which of the following cyclins is linked to the regulation of G1 - S transition?

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

Which statement regarding CDK-cyclin complexes is true?

<p>Sequential activation of CDK-cyclin complexes controls cell cycle progression. (C)</p> Signup and view all the answers

What role does phosphorylation play in the Cdk/cyclin complex?

<p>It changes the shape of the complex, allowing it to function. (C)</p> Signup and view all the answers

Which statement most accurately describes the function of the Cdk/cyclin complex in the cell cycle?

<p>It governs specific checkpoints by phosphorylating target proteins. (C)</p> Signup and view all the answers

What is the correct sequence of events in the activation of the Cdk/cyclin complex?

<p>Cyclin binds to Cdk, complex is phosphorylated, then it phosphorylates the target protein. (A)</p> Signup and view all the answers

How does the activation of a target protein advance the cell cycle?

<p>By changing its shape, leading to downstream effects necessary for progression. (C)</p> Signup and view all the answers

What must occur for the Cdk/cyclin complex to be considered fully active?

<p>It must be phosphorylated in specific locations. (D)</p> Signup and view all the answers

What is the role of p21 in the cell cycle?

<p>It inhibits the activity of Cdk2-cyclin A. (B)</p> Signup and view all the answers

What happens when pRb is phosphorylated?

<p>E2F is activated, promoting the progression of the cell cycle. (C)</p> Signup and view all the answers

What is the function of the tumor suppressor protein p53 in the cell cycle?

<p>It detects DNA damage and stimulates p21 expression. (A)</p> Signup and view all the answers

In the context of negative controls within the cell cycle, what role does E2F play?

<p>E2F drives DNA replication when phosphorylated by pRb. (D)</p> Signup and view all the answers

Which statement most accurately describes the sequence of events triggered by DNA damage?

<p>DNA damage causes p53 activation, which then stimulates p21 production. (B)</p> Signup and view all the answers

Flashcards

G1 Checkpoint

A checkpoint in the cell cycle that ensures the cell is ready to divide, by checking for sufficient cell size, nutrients, growth factors, and the absence of DNA damage.

G2 Checkpoint

A checkpoint in the cell cycle ensuring that all DNA has been accurately replicated before the cell enters mitosis.

M Checkpoint

This checkpoint ensures that all chromosomes are correctly attached to the spindle fibers before the cell enters anaphase.

What is the cell cycle?

The cell cycle is a series of events that takes place in a cell leading to its division and duplication of its DNA (DNA replication) to produce two daughter cells.

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What are Cell Cycle Checkpoints?

Internal control mechanisms that operate at specific points during the cell cycle to ensure that each phase is completed correctly and that the cell only divides when it is appropriate to do so.

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Cyclins

Proteins that act as positive regulators in the cell cycle, controlling the progression from one phase to the next.

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Cyclin-dependent kinases (Cdks)

Enzymes that phosphorylate target proteins, regulating the cell cycle by activating or deactivating them. However, they only become active when bound to cyclins.

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Cyclin types

Different types of cyclins that regulate different parts of the cell cycle, such as cyclins D, E, A, and B.

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Phosphorylation

The process of adding a phosphate group to a molecule, often used to activate or deactivate a protein.

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Cyclin-Cdk complex

The complex formed when a cyclin protein binds to a Cdk. This complex is necessary for the Cdk to become active and control the cell cycle.

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Negative Regulators

Proteins that stop the cell cycle from progressing.

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E2F

A protein complex that regulates cell cycle progression by controlling the transcription of genes needed for DNA synthesis.

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Retinoblastoma protein (Rb)

A protein that acts as a tumor suppressor, holding the cell at the G1 checkpoint and preventing uncontrolled replication.

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Rb

A protein that acts as a brake on the cell cycle by inhibiting the transcription of genes needed for DNA synthesis. When Rb is phosphorylated, it releases E2F, allowing DNA replication.

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p53 protein

A protein that acts as a tumor suppressor, stopping cell division when DNA is damaged and prompting DNA repair. Often absent in cancerous cells.

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p21 (cyclin-dependent kinase inhibitor 1)

A protein that acts as a CDK inhibitor, blocking the activity of kinases that control the cell cycle and preventing uncontrolled replication.

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Cdk2-cyclin A

A specific type of cyclin-CDK complex that is active in late G1 and phosphorylates Rb, releasing E2F.

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Cell Cycle Regulation

The process that controls the timing and progression of events in the cell cycle.

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External Events in Cell Cycle Regulation

External factors that influence the start and stop of cell division.

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Death of a Nearby Cell in Cell Cycle Regulation

A mechanism that can initiate cell division when a nearby cell dies, allowing for regeneration and tissue repair.

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Growth-Promoting Hormones

Hormones that promote cell growth and division.

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Crowding of Cells in Cell Cycle Regulation

A condition where cells stop dividing as they reach high density, preventing uncontrolled growth and maintaining tissue balance.

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Tumour protein p53

A protein that halts the cell cycle when DNA is damaged, preventing mutations.

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Cyclin-dependent kinase inhibitor 1 (p21)

A protein that inhibits the activity of Cdks, acting as a 'break' to pause the cell cycle.

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Proto-oncogenes

Normal cellular genes that, when mutated, can become oncogenes and contribute to uncontrolled cell growth.

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Growth factors

Proteins that bind to growth factor receptors on the cell surface, triggering a cascade of intracellular signaling pathways that ultimately lead to cell cycle progression, growth, and angiogenesis.

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Tumor-suppressor genes

Genes that normally inhibit uncontrolled cell division and act as brakes on the cell cycle. When mutated, they may allow cells to divide unchecked.

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Angiogenesis

The process by which new blood vessels are formed, often stimulated by growth factors and involved in the development and spread of tumors.

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Intracellular signaling pathways

A series of proteins and pathways that are activated by growth factors and other signals, leading to gene transcription, cell cycle progression, and cell proliferation.

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Restriction Point

A key control point during the G1 phase, where the cell decides whether to proceed to DNA replication or exit the cell cycle.

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What are Cyclin-CDK complexes?

These complexes are crucial for progressing through the cell cycle, ensuring that events happen in the right order.

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What is the role of cyclins in the cell cycle?

They bind to cyclin-dependent kinases (CDKs) to activate them, allowing for the phosphorylation of target proteins and driving the cell cycle forward.

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What role do cyclin-dependent kinases (CDKs) play in the cell cycle?

They are enzymes that phosphorylate proteins, which can activate or deactivate them, essentially acting as molecular switches.

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What is the cyclin-dependent kinase (Cdk) complex?

The cyclin-dependent kinase complex (Cdk) is a key regulator of the cell cycle. It consists of two main components: a cyclin protein and a Cdk protein. The cyclin protein acts as an activator, while the Cdk protein is an enzyme that adds phosphate groups to other proteins.

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What are checkpoints, and how are they related to cyclins and CDKs?

They're like a series of checkpoints that ensure the cell is ready to move to the next phase of the cell cycle. These checkpoints assess factors like cell size, DNA integrity, and whether all chromosomes are attached to the spindle fibers.

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Why is phosphorylation important for the cyclin-dependent kinase complex?

The Cyclin-Cdk complex must be phosphorylated at specific locations to become fully active. This phosphorylation event changes the shape of the complex, enabling it to function properly.

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How does the Cdk complex control the cell cycle?

The Cdk complex phosphorylates target proteins, often enzymes involved in cell cycle progression. This phosphorylation alters the shape and activity of the target protein, either activating or deactivating it, and ultimately advancing the cell cycle.

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How do Cyclin-CDK complexes regulate the cell cycle?

The sequential activation of different Cyclin-CDK complexes ensures a precise and regulated progression through the cell cycle.

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What is the role of different cyclins in cell cycle control?

Different types of cyclins bind to Cdk at specific points in the cell cycle. Each cyclin-Cdk combination regulates specific checkpoints, ensuring that the cell divides only when appropriate.

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How does the cyclin-Cdk complex affect target proteins?

The cyclin-Cdk complex, once activated by phosphorylation, phosphorylates target proteins, altering their shape and function. This change in activity of the target protein helps advance the cell to the next stage of the cell cycle.

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Study Notes

Positive Regulation

  • These positive, cell cycle regulators are:
    • Cyclins
    • Cyclin-dependent kinases (Cdk)
  • Cyclins are cell cycle regulatory proteins that switch kinases on and off
  • Cyclins can be categorised as cyclins D, E, A, or B, and each cyclin regulates a different part of the cell cycle
  • Cdk regulate cell cycle events by (de)phosphorylation target proteins as a way of (de)activating them. However, Cdk can only be activated if a cyclin binds to it, creating a cyclin-Cdk complex.

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Description

Test your knowledge on the roles of cyclins and cyclin-dependent kinases (Cdk) in cell cycle regulation. This quiz explores key checkpoints, the functions of proteins like p53 and Rb, and the mechanics of DNA replication monitoring. Discover how these components work together to ensure proper cell division.

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