Cell and Nuclear Division By Idura

Learning Objectives

Haploid and Diploid Cells usually contain two sets of chromosomes. Such cells are described as diploid. This is represented as 2n, where n = the number of chromosomes in one set of chromosomes. A cell which contains only one set of chromosomes is described as haploid. This is represented as n. In humans, therefore, normal body cells are diploid (2n), with 46 chromosomes, and gametes are haploid (n), with 23 chromosomes.

The Cell Cycle During interphase, cells grow to its normal size after cell division and carries out its normal functions. At some point during interphase, a signal may be received that the cell should divide again. If this happens, the DNA in the nucleus replicates so that each chromosome consists of two identical chromatids. This phase of the cell cycle is described as the S phase – S stands for synthesis (of DNA)

Mitosis (Prophase)

Metaphase

Anaphase

Telophase

Reduction Division Reduction Division (Meiosis) is when the number of chromosomes is reduced. Its purpose is to prevent doubling of the chromosome number

Importance of Mitosis Growth Replacement of cells and repair of tissues Asexual Reproduction

Cancer Cancer is one of the most common diseases of developed countries, accounting for roughly one in four deaths, similar to the number of deaths from strokes and coronary heart disease combined. Cancers show us the importance of controlling cell division precisely, because cancers are a result of uncontrolled mitosis.

Carcinogens The term for mutated genes that causes cancer is oncogene. Most mutated cells are either crippled in some way that results in their early death or are destroyed by the body’s immune system. A factor which brings about any mutation is called a mutagen, and is described as mutagenic. Any agent that causes cancer is called a carcinogen and is described as carcinogenic. Hence, some mutagens are carcinogenic

Factors Which Increase Mutation Ionising Radiation and ultraviolet light Chemicals Virus Infection Hereditary Predisposition

Types of Tumor benign tumours, which do not spread from their site of origin, but can compress and displace surrounding tissues malignant (cancerous) tumours, which are far more dangerous since they spread throughout the body, invade other tissues and eventually destroy them. Cells can break off and spread through the blood and lymphatic system to form secondary growth. The spread of cancer this way is called metastasis.

The Flow Chart

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