Question

In very general terms, describe the mechanism of MPF action during the cell cycle. What are the components of MPF and how do they behave during the cell cycle? If possible describe the experiments that elucidated this mechanism.

Short answer

MPF (Maturation-Promoting Factor), also known as CDK1-Cyclin B complex, is crucial in controlling cell cycle progression. It consists of two components: Cyclin-Dependent Kinase 1 (CDK1), which phosphorylates target proteins, and Cyclin B, a regulatory protein controlling CDK1 activity. Cyclin B levels determine MPF activity: increasing Cyclin B leads to MPF activation and mitosis initiation, whereas decreasing Cyclin B inactivates MPF and allows cell cycle continuation. Experiments by Hartwell, Hunt, and Nurse in 1989, involving yeast cells and sea urchin eggs, elucidated MPF's mechanism and led to the discovery of cyclins and cyclin-dependent kinases.

Step-by-step solution

Introduction: MPF and its role in the cell cycle

Maturation-Promoting Factor (MPF), also known as Cyclin-Dependent Kinase 1 (CDK1) - Cyclin B complex, plays a critical role in controlling the cell cycle's progression. It is responsible for triggering the cell's entry into mitosis (the process of cell division) and enabling cells to progress through the cell cycle.

Components of MPF: Cyclin-dependent kinase and Cyclin

MPF consists of two main components: 1. Cyclin-Dependent Kinase 1 (CDK1): A protein kinase that is responsible for phosphorylating target proteins to trigger mitosis. 2. Cyclin B: A regulatory protein that binds to CDK1 and controls its activity. Cyclin B levels fluctuate during the cell cycle, which regulates MPF activity.

MPF behavior during the cell cycle

As cells progress through the cell cycle, Cyclin B levels increase. When Cyclin B binds to CDK1, MPF activity becomes apparent, and the cell is pushed into mitosis. During mitosis, Cyclin B degrades, causing MPF activity to decrease so that the cell can exit mitosis and recommence the cell cycle. In simple terms, MPF's activity during the cell cycle can be summarized as follows: 1. Low Cyclin B levels: CDK1 remains inactive, and MPF's activity is low, keeping the cell in the interphase. 2. Increasing Cyclin B levels: Cyclin B binds to CDK1, activating MPF and initiating mitosis. 3. Decreasing Cyclin B levels: Cyclin B degrades, inactivating MPF, and allowing the cell to exit mitosis.

Experiments that elucidated the MPF mechanism

The experiments performed by Leland Hartwell, Timothy Hunt, and Paul Nurse in 1989 helped to elucidate MPF's mechanism in the cell cycle. They conducted experiments on yeast cells and sea urchin eggs to investigate proteins involved in cell division regulation. As a result, they discovered the cyclins and cyclin-dependent kinases, identifying MPF as a key regulator of the cell cycle. These findings earned them the Nobel Prize in Physiology or Medicine in 2001.

Key concepts

Cyclin-Dependent Kinase 1 (CDK1)

At the heart of cell cycle control is a critical enzyme known as Cyclin-Dependent Kinase 1 (CDK1). CDK1 is the engine that drives the cell through the complex journey of division.

Think of it as the conductor of an orchestra, ensuring that each section of the cell-cycle 'music' is played at the right time. When CDK1 partners with another protein called Cyclin B, it triggers a cascade of events that push the cell into the mitotic phase. This partnership is crucial because it is meticulously regulated by the cell, allowing for orderly progression and preventing mistakes that could lead to cell damage or disease.

Cyclin B

Imagine Cyclin B as a gatekeeper, determining when the cell can enter into the critical phase of division known as mitosis.

It fluctuates in level throughout the cycle, peaking right when the cell needs to start dividing, and falling off when it's time to return to normal functions post-division. This rise and fall act almost like a clock. When Cyclin B levels are high, it binds to CDK1, giving the green light to proceed with mitosis. As the cell passes through mitosis, Cyclin B breaks down, bringing the process to a halt—literally like clockwork.

Mitosis

Mitosis is the phase of the cell cycle where a cell divides to form two identical daughter cells, each with the same genetic material as the original.

This process is like a well-rehearsed play, where every actor knows their cue. CDK1 and Cyclin B are the directors making sure every part of the cell performs correctly, from condensing chromosomes to redistributing cell organelles, ensuring that each newly formed cell is equipped to begin life anew.

Cell cycle regulation

Regulating the cell cycle is critical, as errors in this process can lead to unchecked cell growth, a hallmark of cancer.

The cell cycle is controlled by various checkpoints, much like a roller coaster ride is overseen by inspections to make sure it's safe to proceed. The MPF, or CDK1-Cyclin B complex, governs one of the most crucial checkpoints—the transition from interphase into mitosis. With precise regulation, the cell can maintain equilibrium between growth and division, acting as a fail-safe against potential errors.

Nobel Prize in Physiology or Medicine

The ensemble work of three scientists, Leland Hartwell, Timothy Hunt, and Paul Nurse, unveiled the curtains from the mystifying process of cell cycle control.

They delved into the molecular mechanics of cells, ultimately identifying key components like MPF, cyclins, and cyclin-dependent kinases. This breakthrough was monumental, furnishing a new understanding of cell growth and its disorders such as cancer. Their discovery not only unraveled a fundamental aspect of biology but also laid the groundwork for therapeutic interventions. In recognition of their pioneering work, they were awarded the Nobel Prize in Physiology or Medicine in 2001.