Question

What step in the cell cycle represent irreversible commitment

Answer 1

Cell cycle–the existence of a cell from the moment of its formation in the process of dividing the mother cell to its own division (including this division) or death.The cell cycle consists of interphase and mitosis (cell division).

As well

Under cellular aging, scientists understand the irreversible blocking of the cell cycle after a number of divisions, a decrease in the level of metabolism and energy exchange.

Answer 2

Irreversible commitment in the cell cycle is primarily associated with a checkpoint called the "restriction point" or "R-point" (also known as the "start point" in yeast cells). The restriction point is a critical juncture in the G1 phase of the cell cycle, where a cell makes the decision to enter the S phase and commit to cell division.

Here's a detailed explanation of the restriction point and its role in the cell cycle:

1. G1 Phase: The cell cycle is divided into several phases, and the G1 phase, which stands for "Gap 1," is the phase that follows cell division (mitosis or meiosis) and precedes DNA replication. During G1, the cell is preparing for DNA synthesis (S phase) and growth.

2. Cell Cycle Checkpoints: Throughout the cell cycle, there are checkpoints that serve as quality control mechanisms to ensure that the cell is ready to proceed to the next phase. The primary checkpoints are the G1 checkpoint (restriction point), the G2 checkpoint, and the spindle checkpoint during mitosis.

3. Restriction Point (R-Point): The G1 checkpoint, or the restriction point, is a crucial decision point in the cell cycle. At this stage, the cell evaluates its internal and external conditions. Factors like the availability of nutrients, proper cell size, and absence of DNA damage are assessed.

4. Irreversible Commitment: The key feature of the restriction point is that it represents an irreversible commitment to cell division. Once a cell passes this checkpoint and commits to entering the S phase, it will eventually go through the entire cell cycle, regardless of external conditions. This means that if a cell successfully passes the restriction point, it is committed to replicating its DNA and dividing.

5. Cyclin-Dependent Kinases (CDKs): Progression through the cell cycle is regulated by a family of proteins called cyclin-dependent kinases (CDKs) and their associated regulatory proteins called cyclins. At the restriction point, the activity of CDKs is tightly controlled. When certain conditions are met, specific cyclins combine with CDKs, resulting in the activation of CDKs. Active CDKs phosphorylate target proteins, promoting the cell's entry into the S phase and initiating DNA replication.

6. Regulatory Proteins: Regulatory proteins, such as p53 and Rb (Retinoblastoma protein), play a vital role in controlling the restriction point. If DNA damage or unfavorable conditions are detected, these proteins can halt cell cycle progression by inhibiting CDK activity and, as a result, prevent the cell from passing the restriction point. This serves as a safeguard to avoid cell division under unfavorable circumstances.

In summary, the restriction point (G1 checkpoint) in the cell cycle represents the irreversible commitment to cell division. When a cell passes this checkpoint, it commits to entering the S phase and eventually completing the entire cell cycle. The decision to pass this checkpoint is based on the evaluation of various factors, and it is tightly regulated by cyclin-dependent kinases and regulatory proteins.