Mitosis: Stages and Key Events

The process of mitosis is divided into several distinct stages, each characterized by specific cellular events. This page provides a comprehensive overview of the entire mitotic process, from interphase through to cytokinesis.

Interphase (90% of Cell Cycle)

Interphase is the preparatory phase for cell division, consisting of three sub-stages:

1. G1 (Gap 1): The cell grows in size.
2. S (Synthesis): DNA replication occurs.
3. G2 (Gap 2): Further growth in preparation for mitosis.

Vocabulary: Interphase - The stage of the cell cycle where the cell prepares for division but no actual division takes place.

Prophase

During prophase, several key events occur:

• The nuclear envelope breaks down and disappears.
• Chromatin condenses into visible chromosomes.
• In animal cells, centrioles move to opposite poles of the cell.
• Spindle fibers begin to form, collectively known as the spindle apparatus.

Definition: Spindle apparatus - The structure composed of microtubules that guides chromosome movement during cell division.

Metaphase

In this stage:

• Spindle fibers attach to the centromeres of chromosomes.
• Chromosomes align at the cell's equator, forming the metaphase plate.

Highlight: The alignment of chromosomes at the metaphase plate is a crucial event in mitosis A Level Biology Edexcel and other curricula.

Anaphase

Anaphase is characterized by:

• Division of centromeres, separating sister chromatids.
• Rapid movement of chromatids (now called chromosomes) to opposite poles.
• Mitochondria gathering around spindle fibers to provide energy.

Example: If cells are treated with chemicals that destroy the spindle, chromosomes remain at the equator, unable to reach the poles.

Telophase and Cytokinesis

The final stages of mitosis include:

• Chromosomes reaching their respective poles and decondensing.
• Reformation of the nuclear envelope and nucleolus.
• Disintegration of spindle fibers.
• Division of the cytoplasm (cytokinesis) to complete cell division.

Vocabulary: Cytokinesis - The process of cytoplasmic division that completes cell division.

Understanding these stages is crucial for answering AQA A Level Biology mitosis exam questions and mastering the detailed mitosis stages a level biology gcse content.