Edexcel GCSE Biology: Mitosis and Uncontrolled Cell Division Study Notes
Introduction to Mitosis
Mitosis is defined as a process of nuclear division that results in the formation of two daughter cells which are genetically identical to each other and to the parent cell.
These resulting daughter cells are diploid. In humans, the diploid number is defined as pairs of chromosomes, totaling chromosomes in each cell.
Mitosis accounts for the production of all body cells (somatic cells) from the original zygote, with the sole exception of gametes (sex cells).
Biological Requirements for Mitosis
Mitosis is a fundamental biological process required for three primary purposes:
Growth: The process allows for the production of new cells, enabling an organism to increase in size and complexity.
Repair: Mitosis is essential for replacing cells that have become damaged or have died over time.
Asexual Reproduction: Some organisms utilize mitosis to produce offspring. Because the division produces genetically identical cells, the offspring are clones of the parent organism.
The Three Parts of the Cell Cycle
The cell cycle describes the entire life of a cell, divided into three distinct phases that occur in sequence:
Interphase: This phase occurs just before the actual process of mitosis begins. During interphase, the DNA within the nucleus copies itself exactly. This replication results in the formation of x-shaped chromosomes, where each side of the "x" is an identical copy of the genetic material.
Mitosis: This is the specific stage of nuclear division where the chromosomes are organized and separated.
Cytokinesis: Following the division of the nucleus, the cell's cytoplasm and cell membrane divide. This physical splitting produces two separate daughter cells, each containing a full copy of every chromosome from the parent cell.
The Detailed Stages of Mitosis
After interphase is complete, the mitosis phase itself proceeds through a specific, ordered series of stages:
Prophase: The DNA condenses, causing the chromosomes to become visible under a microscope. Simultaneously, the nuclear membrane begins to break down.
Metaphase: The chromosomes align themselves along the middle of the cell. This central line is referred to as the equator or the metaphase plate.
Anaphase: Spindle fibres (also referred to as cell fibres) attach to the chromosomes and split them down the center. One chromatid from each chromosome is pulled toward opposite sides (poles) of the cell.
Telophase: To complete the nuclear division, new membranes form around the chromosomes located at each end of the cell, creates two distinct nuclei.
Calculating Cell Proliferation
In biological studies and examinations, it is often necessary to calculate the total number of cells resulting from a specific number of consecutive divisions.
The mathematical formula for this calculation is , where represents the total number of cell divisions.
Example Scenario: If a process starts with cell and it undergoes successive divisions, the calculation would be .
Result: cells.
Regulation of Cell Division and Cancer
Cell division is a highly regulated process essential for maintenance. For instance, cells in the human intestines are constantly undergoing mitosis to replace cells that are shed as food particles move through the digestive tract.
The cell cycle is regulated by many different genes to ensure that cells only divide when necessary and cease division when they are no longer required.
Cancer: This condition is caused by mutations in the DNA of cells. These mutations lead to a breakdown in the control mechanisms of the cell cycle, resulting in uncontrolled cell growth and division.
Tumour Formation: The result of this uncontrolled division is the formation of a mass of cells known as a tumour.