cell cycle

• body cells in multicellular organisms divide to produce new cells as part of a series of stages called the cell cycle
• the stage of the cell cycle when the cell divides is called mitosis
• multicellular organisms use mitosis to grow or replace cells that have been damged
• the end of the cell cycle results in two new cells identical to the original cell, with the same number of chromosomes
• Growth and DNA replication:

  1. in a cell thats not dividing the DNA is spread out in long strings
  2. the cell has to grow and increase the amount of subcellular structures (e.g mitochondria and ribosomes)
  3. it then duplicates its DNA - theres one copy for each new cell. DNA forms X-shaped chromosomes. each 'arm' of the chromosome is an exact duplicate of the other
• Once DNA and contents are copied the cell is ready for mitosis:

  4. the chromosomes line up at the centre and cell fibres pull them apart. two arms of each chromosome go to opposite ends of the cell

  5. membranes form around each sets of chromosomes. these become nuclei of the two new cells - the nucleus has divided

  6. lastly the cytoplasm and cell membrane divide
• After mitosis, the cell has produced two new daughter cells which contain exactly the same DNA - theyre identical