B2.2 mitosis

• all organisms require a continuous supply of new cells for:

  • growth
  • repair
  • development
• the process in which new cells are generated is called the “cell cycle“
• 1. the cell grows in size and increases the number of sub cellular structures (eg. mitochondria and ribosome)
• 2. DNA is duplicated so the two new cells have a full set of DNA
• when a cell is not dividing DNA is spread out in long strings
• once the cell prepares for division DNA condenses into chromosomes
• eukaryotic cells (animals) contain two copies of each chromosome one copy is from the mother and one from the father
• humans have 23 pairs of chromosomes
• so humans actually have 46 chomosomes
• as the cell continues to repair for division it duplicates each of the 46 chromosomes (the duplicate stays attached to the original)
• the duplicates form an X shape
• once the the cell is ready to divide all 46 of the cells chromosomes line up in the centre of the cell
• cell fibres pull the arms of the chromosomes to each side of the cell, breaking them in half
• 3. cell divison (cytokinesis)
• cytokinesis: the entire cell divides to form two identical daughter cells
• the DNA divides into two