Cells and control Revision Notes

Purpose of Mitosis

Mitosis is the process of cell division that produces two, genetically identical diploid daughter cells. This is essential for organismal growth, repair of damaged tissues, and asexual reproduction. It ensures that new cells have the same genetic information as the parent cell.

Process of Mitosis

Before mitosis, the cell's chromosomes are replicated. During mitosis, these replicated chromosomes (each consisting of two sister chromatids) align, and the sister chromatids are then separated, moving to opposite ends of the cell. Finally, the cell divides, forming two new daughter cells. Each daughter cell receives a full and identical set of chromosomes to the parent cell's nucleus, maintaining the diploid number.

Genetic Outcome

The outcome of mitosis is the formation of two daughter cells that are genetically identical to each other and to the original parent cell. These cells are diploid, meaning they contain two complete sets of chromosomes. This genetic fidelity is vital for maintaining the integrity of an organism's genetic material across cell generations for bodily functions like tissue regeneration.

The Cell Cycle: Interphase

The cell cycle involves a period of growth and DNA replication (interphase) followed by cell division (mitotic phase). Interphase is crucial for preparing the cell for division. During the S phase of interphase, the cell's DNA is duplicated, leading to chromosomes that consist of two identical sister chromatids joined at a centromere. The cell also grows and synthesises proteins during the G1 and G2 phases.

Stages of Mitosis and Cytokinesis

Mitosis is the division of the nucleus, ensuring each new cell receives an identical set of chromosomes. It comprises several distinct stages:

1. Prophase: Chromosomes condense and become visible, the nuclear envelope starts to break down, and the spindle fibres begin to form.
2. Metaphase: Chromosomes line up individually along the cell's equator (metaphase plate).
3. Anaphase: Sister chromatids separate and are pulled to opposite poles of the cell by the shortening spindle fibres.
4. Telophase: Chromosomes decondense at opposite poles, new nuclear envelopes form around each set of chromosomes, and the spindle fibres disappear.

Following nuclear division, Cytokinesis occurs, which is the division of the cytoplasm, resulting in two separate, genetically identical daughter cells.

What is Mitosis?

Mitosis is a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth. It ensures genetic consistency between parent and daughter cells.

Mitosis in Growth

Multicellular organisms grow by increasing the number of their cells through mitosis. From a single fertilized egg (zygote), repeated mitotic divisions form a complex organism, adding cells to become larger and more developed.

Mitosis in Repair and Replacement

Mitosis is essential for repairing damaged tissues and replacing dead or worn-out cells. For instance, when you cut yourself, new skin cells are generated via mitosis to heal the wound. Red blood cells and skin cells are constantly replaced through this process.

Mitosis in Asexual Reproduction

In asexual reproduction, a single parent organism produces genetically identical offspring. Mitosis is the cellular basis for this process in organisms like bacteria, yeast, and some plants (e.g., runners in strawberries) and fungi. The offspring are clones of the parent.

What is Cancer?

Cancer is a disease characterised by the uncontrolled division of abnormal cells. Rather than following the body's normal regulatory processes for cell growth and division, cancerous cells multiply continuously.

Cell Division Normal vs. Abnormal

Normally, cell division is a highly regulated process where cells divide only when needed for growth or repair. In cancer, genetic changes disrupt these controls, causing cells to divide excessively and without proper regulation.

Formation of Tumours

Uncontrolled cell division leads to the formation of a mass of cells called a tumour. Tumours can be either benign (non-spreading) or malignant (cancerous, with the ability to invade and spread).

Causes of Cell Changes

Changes in cells that lead to cancer are often due to mutations in specific genes that control cell growth and division. These mutations can be caused by various factors, including exposure to carcinogens (e.g., UV radiation, tobacco smoke) or inherited genetic predispositions.