Question

Which one of the following precedes reformation of nuclear envelope during M-phase of cell cycle ?

• A. Decondensation of chromosomes and reassembly of nuclear lamina
• B. Transcription from chromosomes and reassembly of nuclear lamina
• C. Formation of the contractile ring and formation of phragmoplast
• D. Formation of the contractile ring and transcription from chromosomes

Answer 1

The Correct Option is A

The question asks which event precedes the reformation of the nuclear envelope during the M-phase of the cell cycle. To answer this, we need to understand the sequence of events that occur during the M-phase, specifically during telophase when the nuclear envelope reforms.

During the M-phase (mitosis), the cell undergoes several stages: prophase, metaphase, anaphase, and telophase.

1. Prophase: Chromosomes condense and become visible. The nuclear envelope breaks down.
2. Metaphase: Chromosomes align at the cell's equatorial plate.
3. Anaphase: Sister chromatids separate and move towards opposite poles.
4. Telophase: This is the stage where the reformation of the nuclear envelope occurs.

In telophase, two critical processes occur:

1. Decondensation of Chromosomes: The chromosomes begin to decondense, reversing the process that occurred during prophase.
2. Reassembly of Nuclear Lamina: The nuclear envelope reforms around each set of chromosomes, and the nuclear lamina reassembles supporting the new envelops.

Based on the above explanation, the correct answer is clearly Decondensation of chromosomes and reassembly of nuclear lamina as these occur before and consequently during the nuclear envelope reformation. This eliminates the other options:

• Transcription from chromosomes and reassembly of nuclear lamina: Transcription initiation before complete reformation of the nuclear envelope is not common.
• Formation of the contractile ring and formation of phragmoplast: This mainly pertains to cytokinesis, not nuclear envelope reformation.
• Formation of the contractile ring and transcription from chromosomes: Again, this relates more to the final stages of cell division.

Therefore, the correct sequence pertaining to the nuclear envelope involves the Decondensation of chromosomes and reassembly of nuclear lamina. The answer choice reflects these events correctly, occurring just prior to complete nuclear envelope reformation in telophase.