1.2.2 Mitosis & The Cell Cycle

• Body cells in multicellular organisms divide to produce new cells as part of a series of stages called the cell cycle.
• What is mitosis?

  The stage of the cell cycle where the cell divides.
• Why do multicellular organisms use mitosis?

  To grow or replace cells that have been damaged.
• Growth & DNA replication:

  • In a cell that’s not dividing, the DNA is all spread out in long strings.
  • Before it divides, the cell has to grow and increase the amount of subcellular structures it has, such as mitochondria and ribosomes.
  • It then duplicates its DNA so there’s one copy for each new cell.
  • The DNA is copied and forms X-shaped chromosomes.
  • Each ‘arm’ of the chromosome is an exact duplicate of the other.
• Mitosis:

  • Once its contents and DNA have been copied, the cell is ready for mitosis.
  • The hormones line up at the centre of the cell and cell fibres pull them apart.
  • The two arms of each chromosome go to opposite ends of each cell.
  • Membranes form around each of the sets of chromosomes and become the nuclei of the two new cells.
  • Lastly, the cytoplasm and cell membrane divide.
  • Two daughter cells have now been produced and are identical to both each other and their parent cell.
• Cell division by mitosis is important in…?

  The growth and development of multicellular organisms.
• Binary fission:

  1. The circular DNA and plasmid(s) replicate.
  2. The cell gets bigger and the circular DNA strands move to opposite ends of the cell.
  3. The cytoplasm begins to divide and new cell walls begin to form.
  4. The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s).