Question

a diagram of the cell cycle is shown. it maps the phases of the cell cycle and the checkpoints by which certain criteria must be met for the cell cycle to advance to the next phase. what statements describe how a cell may respond at a checkpoint? the cell may undergo apoptosis. the cell cycle can skip mitosis and continue to the g₁ phase if an error is detected. the cell can temporarily halt cell cycle progression. the cell may initiate the next phase in the cell cycle. the cell can reverse the cycle to correct a mistake.

Explanation:

• Apoptosis: If a cell has irreparable damage at a checkpoint (e.g., DNA damage that cannot be fixed), it may undergo apoptosis (programmed cell death) to prevent the propagation of faulty cells.
• Halt cell cycle: Checkpoints (like \(G_1\), \(G_2\), and \(M\) checkpoints) can cause the cell cycle to pause. For example, at the \(G_1\) checkpoint, if the cell is not ready (e.g., not enough nutrients, damaged DNA), proteins (e.g., p53 - related proteins) can stop the cell cycle progression until the issues are resolved.
• Initiate next phase: If all the criteria at a checkpoint are met (e.g., at the \(G_1\) checkpoint: undamaged DNA, proper cell size, enough nutrients), the cell will proceed to the next phase (e.g., from \(G_1\) to \(S\) phase).

• Skipping mitosis: The cell cycle is a sequential process. Skipping mitosis (\(M\) phase) and going back to \(G_1\) is not a normal response at a checkpoint. The cell cycle phases \(G_1\to S\to G_2\to M\) are sequential, and skipping \(M\) would lead to cells with abnormal ploidy (chromosome number) if it were a regular occurrence.
• Reversing the cycle: The cell cycle is a unidirectional process. While there are repair mechanisms (e.g., DNA repair in \(S\) or \(G_2\) phase), the cycle does not reverse in the sense of going back multiple phases to “correct a mistake” in a general checkpoint - related response.

Answer:

• The cell may undergo apoptosis.
• The cell can temporarily halt cell cycle progression.
• The cell may initiate the next phase in the cell cycle.