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Chapter 23: Problem 28

What would be the effect of a drug that inhibited the breakdown of cyclin B?

Short Answer

Expert verified
Inhibiting cyclin B breakdown would result in mitotic arrest, preventing cells from exiting mitosis.

Step by step solution

01

Understanding Cyclin B Function

Cyclin B is crucial for the regulation of the cell cycle. It partners with Cdk1 to form the maturation-promoting factor (MPF), which is essential for a cell's transition from the G2 phase into mitosis (M phase).
02

Analyzing Cyclin B Breakdown

During cell cycle progression, cyclin B must be broken down for a cell to exit mitosis and enter the G1 phase. The degradation of cyclin B is necessary to inactivate MPF, thus allowing the cell to complete mitosis and prepare for the next cycle.
03

Effect of Inhibition

If a drug inhibits the breakdown of cyclin B, the cell would be unable to inactivate MPF. This would prevent the cell from successfully exiting mitosis, potentially leading to mitotic arrest where the cell remains stuck in the M phase.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Cell Cycle Regulation
Cell cycle regulation is the process that ensures cells progress through the phases of growth and division in a controlled manner. This regulation is vital for maintaining cellular health and function. The cell cycle comprises several phases: G1, S, G2, and M, during which the cell grows, duplicates its DNA, and divides.

A series of checkpoints throughout the cycle ensures that each phase is completed accurately. If errors are detected, the cycle can pause for repairs, ensuring that faulty cells do not propagate. These checkpoints are governed by
  • Cyclins, which are proteins that regulate the passage through different stages by activating cyclin-dependent kinases (CDKs).
  • CDKs, which are enzymes activated by cyclins to initiate specific cell cycle events.
Proper cell cycle regulation prevents uncontrolled cell growth, contributing to the prevention of diseases such as cancer.
Maturation-Promoting Factor (MPF)
Maturation-Promoting Factor (MPF) is a critical component in cell cycle regulation. MPF is a complex formed by the interaction of Cyclin B and Cyclin-Dependent Kinase 1 (Cdk1).

This complex plays an essential role in initiating the M phase, which includes mitosis. MPF's primary function is to trigger the cell's entry into mitosis from the G2 phase. It does so by:
  • Phosphorylating various proteins that initiate the breakdown of the nuclear envelope.
  • Promoting chromosome condensation and the assembly of the mitotic spindle, a structure that separates chromosomes during mitosis.
The activity of MPF is tightly controlled and must be turned off by the end of mitosis to allow the cell to divide properly and reset for the next cycle. Inhibiting Cyclin B breakdown would mean MPF remains active, resulting in failure to exit mitosis.
Mitotic Arrest
Mitotic arrest is a condition where a cell is unable to successfully complete mitosis. This often occurs when mechanisms controlling cell cycle progression are disrupted, such as with the inhibition of Cyclin B breakdown.

Mitotic arrest can have several consequences for the cell:
  • The cell remains stuck in mitosis, unable to proceed to the G1 phase, leading to cell cycle disruption.
  • This state can cause cellular damage, as the cell cannot complete division, possibly resulting in cell death or dysfunction.
Prolonged mitotic arrest signals the cell to activate programmed cell death pathways, such as apoptosis, to prevent compromised cells from propagating and potentially leading to disease.

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