In which phase of the cell cycle are chromosomes inactive, highly condensed, and not transcribed into messeng… - Haryana CHO - 2022

Haryana CHO - 2022

Applied Physiology

Easy

Appeared in: Haryana CHO - 2022

Explanation

The M phase (Mitosis) is characterized by the highest level of chromosome condensation.
This supercoiling is necessary to organize and separate the duplicated chromosomes into two daughter cells without tangling or damage.
The tightly packed structure of mitotic chromosomes physically blocks RNA polymerase and other transcription factors from accessing the DNA.
As a result, gene transcription into messenger RNA (mRNA) is globally shut down during the M phase.

Option A: The G₁ phase is a period of active cell growth and protein synthesis. Chromosomes are decondensed (as euchromatin) to allow for high levels of transcription.
Option B: The S phase is when DNA replication occurs. The chromatin must be in a relaxed, open state to allow DNA polymerase to access and duplicate the entire genome. Transcription still occurs, although at a reduced rate compared to G1.
Option D: The G₂ phase is the final preparation stage before mitosis. The cell continues to grow and produce proteins, so chromosomes remain decondensed and transcriptionally active.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Chromosome condensation and transcriptional activity during the cell cycle as background academic context rather than a clinical decision trigger.
Understanding the cell cycle is fundamental to oncology. Cancer is characterized by uncontrolled cell division, often due to defects in cell cycle checkpoints.
Many chemotherapy drugs, known as antimitotic agents (e.g., Vinca alkaloids, Taxanes), specifically target the M phase. They disrupt the formation of the mitotic spindle, arresting cells in mitosis and leading to apoptosis (programmed cell death).
What if? If a cell had a defect in the M-phase checkpoint (spindle checkpoint), it might divide with incorrectly segregated chromosomes. This leads to aneuploidy (abnormal number of chromosomes), a hallmark of many cancer cells, which contributes to genetic instability and tumor progression.

How to Approach the Question

First, identify the key terms in the question: 'inactive', 'highly condensed', and 'not transcribed'.
Next, recall the primary function of each phase of the cell cycle.
Interphase (G₁, S, G₂) is the 'living' phase where the cell grows, replicates its DNA, and carries out its normal functions. This requires the DNA to be accessible, so it is in a loose, decondensed state (chromatin) to allow for transcription and replication.
The M phase (Mitosis) is the 'division' phase. Its main job is to separate the chromosomes. To do this neatly, the long chromatin threads must be tightly packed into compact chromosomes.
Logically connect 'highly condensed' with 'inactive'. When the DNA is tightly wound, the enzymes needed for transcription cannot access it.
Therefore, the only phase that fits all three criteria—condensed, inactive, and not transcribed—is the M phase.

Concept Tested & Keywords

Concept Tested: Chromosome condensation and transcriptional activity during the cell cycle.
Stem keywords: cell cycle, chromosomes, inactive, highly condensed, not transcribed, messenger RNA, mRNA
Lead-in keywords: In which phase
Negative lead-in flag: false

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