MITOSIS

• Interphase

  Replication of DNA, the two copies of DNA remain joined at the centromere
• Prophase


  -Chromosomes first become visible as long thin threads (which later -shortens and thickens)

  -Animal cells have centrioles (two cylindrical organelles) which move to opposite ends of the cell

  -Spindle fibres develop from the centrioles and span from pole to pole (centrioles not necessary in plant cells)

  -The nucleolus disappears

  -Nuclear envelope breaks down, leaving chromosomes free in the cytoplasm

  -Chromosomes are drawn to equator of cell by spindle fibres attached to centromere
• Metaphase

  -Chromatid: identical copy of DNA from the parent cell

  -In this phase chromosomes are made up of two chromatids joined at the centromere

  -Microtubules from poles attach to centromere

  -Chromosomes pulled along spindle apparatus
• Anaphase


  -Centromeres divide into two

  -Spindle fibres pull individual chromatids and move rapidly to their opposite poles (now refer to them as chromosomes)

  -Energy for this process provided by mitochondria (gather around the spindle fibres
• Telophase and cytokinesis

  -Chromosomes reach poles, become long and thinner then disappear leaving chromatin

  -Spindle fibres disintegrate

  -Nuclear envelope and nucleus reform

  -Cytoplasm divides (cytokinesis)
• STAGES OF MITOSIS

  
• Cancer

  Cancer is caused by a growth disorder in cells, and is the result of damage to the genes that regulate mitosis.
• What is a tumor?

  A group of abnormal cells constantly expanding in size
• When does a tumor become cancerous?

  When it changes from benign to malignant
• Treatment of cancer

  Killing dividing cells by blocking part of the cell cycle. Mitosis ceases therefore stopping cancer growth.
• How do drugs (chemotherapy) disrupt the cell cycle?

  -preventing the DNA from replicating

  -inhibiting metaphase by interfering with spindle formation
• What is the issue with chemotherapy?

  It also disrupts the cell cycle of healthy cells, however cancer cells have a particularly fast rate of division and so are damaged more.