The eukaryotic cell cycle is controlled at several points, which of these statements is not true?

Options

A. Cell growth Is assessed at the `G_(1)//S` checkpoint
B. DNA replication is assessed at the `G_(2)//M` checkpoint
C. Environmental conditions are assessed at the `G_(0)` checkpoint.
D. The chromosomes are assessed at the spindle checkpoint.

Answer

To determine which statement about the eukaryotic cell cycle is not true, we need to review the key checkpoints in the cell cycle and their functions. Here's a step-by-step breakdown of the information provided:

### Step-by-Step Solution:

1. **Understanding the Cell Cycle**: The eukaryotic cell cycle consists of several phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). Each phase has specific functions and checkpoints that ensure the cell is ready to proceed to the next phase.

2. **Identifying Checkpoints**: There are three main checkpoints in the eukaryotic cell cycle:
- **G1 Checkpoint**: This checkpoint occurs at the end of the G1 phase before the cell enters the S phase. It checks for sufficient nutrients, cell size, DNA integrity, and the presence of necessary enzymes. If conditions are not favorable, the cell may enter a resting state known as G0.
- **G2 Checkpoint**: This occurs at the end of the G2 phase before the cell enters mitosis (M phase). It checks whether DNA has been correctly replicated and ensures there are no errors in the DNA.
- **M Checkpoint (Spindle Checkpoint)**: This checkpoint occurs during metaphase of mitosis. It ensures that spindle fibers are correctly attached to the chromosomes before the cell proceeds to anaphase.

3. **Evaluating Statements**: The question asks which statement is not true regarding the checkpoints in the eukaryotic cell cycle. Based on the information provided:
- There are indeed checkpoints at G1, G2, and M phases.
- The G0 phase does not have a checkpoint; it is a resting state for cells that are not ready to divide.
- The checkpoints serve to assess various conditions necessary for successful cell division.

4. **Conclusion**: The statement that is not true is likely related to the G0 phase, as it is not a checkpoint but rather a state where the cell is not actively preparing to divide.

### Final Answer:
The statement that is not true is related to the G0 phase, as it does not have a checkpoint.

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