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The Cell Cycle
The cell cycle has three stages:
1. Interphase: this stage occupies most of the cell cycle and is known as resting phase as no
division takes pace. This is divided into three parts:
I. First growth (G) phase: when proteins from which cell organelles are synthesised
II. Synthesis (S) phase: when DNA is replicated
III. Second growth (G) phase: when organelles grow and divide and energy stores
2. Nuclear division: when nucleus divides either into two (mitosis) or four (meiosis)
3. Cell division: follows nuclear division. This is the process by which the whole cell divides
either into two or four.
Length of the complete cycle varies amongst the organisms. Typically a mammalian cell takes about
24 hours to complete a cycle of which 90% is interphase
Cancer is caused by growth disorder of cells. It is a result of damage to genes that regulate mitosis
and cell cycle. This leads to uncontrolled growth of cells. As a result tumour (abnormal cells) develops
and continuously expands in size.