3.8 The cell cycle

Interphase: Occupies most of the cell cycle, called the resting phase because no division takes place Nuclear division: When the nucleus divides either into two (mitosis) or four (meiosis) Cytokinesis: Division of the cytoplasm, which follows nuclear division and the cytoplasm divides to make two new cells (mitosis) or 4 new cells (meiosis)

It takes around 24 hours 90% of it is interphase

.Uncontrolled growth and division of cells A group of diseases caused by a growth disorder in cells. When there is damage to the genes that regulate mitosis and the cell cycle So as a result a group of abnormal cells (a tumour) develops.

Malignant is cancerous, whilst benign isn’t, and doesn’t invade organs or tissues as the group of cells are held together in a membrane. It becomes cancerous if the tumour changes from benign to malignant

. Growth: Increase the size of a tissue during development . Repair: Replace dead and worn out cells . Asexual reproduction: It produces an identical copy of the parent cell

The environment of the cell, Two types of gene: mutations in one of these genes results in uncontrolled mitosis Mutant cells are structurally and functionally different from normal cells, and most mutated cells die. However any that survive can form clones of themselves and form tumours

. Malignant tumours grow rapidly, are less compact, and are more likely to be life threatening . Benign tumours grow more slowly, are more compact, and are less likely to be life threatening

It involves killing dividing cells by blocking parts of the cell cycle, so it is disrupted. These drugs disrupt the cell cycle by: . Preventing DNA from replicating . Inhibiting the metaphase stage of mitosis by interfering with the spindle fibre formation

• They also disrupt the cell cycle of normal cells, eg ones that divide rapidly like hair cells, so they are vulnerable to damage. This explains frequent hair loss. However, the drugs are more effective against rapidly dividing cells, like cancer cells.