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:
- G1 (Gap 1): The cell grows in size.
- S (Synthesis): DNA replication occurs.
- 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.