Uncontrolled Cell Division & Tumour Formation (DP IB Biology)

Mutations in Genes Controlling Cell Cycle

• Mutations of the genes that control the cell cycle may lead to cancer

• Two types of genes are typically involved with the development of cancer:

  • Proto-oncogenes code for proteins which stimulate normal cell division

    • These genes are converted to oncogenes once they mutate

    • This results in an increase in the protein product produced or proteins which are permanently activated

    • Leading to uncontrolled cell division which may result in cancer

  • Tumour-suppressor genes code for proteins which inhibit cell division or promote controlled cell death (known as apoptosis) should the nucleus contain damaged DNA

    • Mutations in these genes may result in no or reduced protein product or proteins which are permanently deactivated

    • Leading to uncontrolled cell division and possibly cancer

Types of Tumours

• Cancers demonstrate how important it is that cell division is precisely controlled, as cancers arise due to uncontrolled mitosis

• Cancerous cells divide repeatedly and uncontrollably, forming a tumour (an irregular mass of cells)

• A typical tumour contains around a thousand million cancerous cells by the time it is detected

Types of tumour

• Tumours have different characteristics depending on whether they are cancerous (malignant) or non-cancerous (benign)

• All tumours may cause harm to the body by:

  • Damaging the organ in which the tumour is located

  • Causing blockages or obstructions

  • Damaging other organs by exerting pressure

Malignant tumours

• Malignant tumours are cancerous

• Malignant tumours cause cancer by growing rapidly, then invading and destroying surrounding tissues

  • Cells within malignant tumours secret chemicals that cause the formation of blood vessels to supply the tumour with nutrients, growth factors and oxygen

  • These tumours are known as primary tumours and this is where cancer starts to develop

• Cells can break off these primary tumours and spread to other parts of the body through the bloodstream or lymphatic system, this is called metastasis

  • Metastasis causes the spread of tumours to other places in the body, affecting multiple organs

  • Tumours that develop from cells that broke off the primary tumour are known as secondary tumours

  • When removed through surgery, malignant secondary tumours can still grow back

• The formation of malignant tumours can be initiated by carcinogens such as:

  • UV or X-ray exposure

  • Tobacco from cigarettes

  • Asbestos

  • Processed meat

Cancer formation diagram

Stages in the development of cancer

Benign tumours

• Benign tumours are not cancerous

• These tumours grow slowly 

• Benign tumours do not invade other tissues and do not metastasise, unlike malignant tumours

• These tumours can cause damage such as blockages or by exerting pressure on the organ it is growing in or those surrounding it

• When removed, benign tumours do not usually grow back

• The formation of benign tumours can be initiated by:

  • Inflammation or infection

  • Injury

  • Diet

  • Genetics

  • Toxins and radiation

• Examples of benign tumours are:

  • Polyps found in the nose, colon and ovaries

  • Non-cancerous brain tumours

  • Warts, caused by a viral infection