Chromosomes and Mitosis

• • In order to survive and grow, our cells have got to be able to divide. And that means our DNA as well...
  • Chromosomes contain Genetic information

  1. The nucleus of a cell contains chromosomes
  2. Chromosomes are coiled up lengths of DNA molecules
  3. Each chromosome carries a large number of genes
  4. Different genes control the development of different characteristics e.g. hair colour
  5. Body cells normally have two copies of each chromosome
  6. There are 23 pairs of chromosomes in a human cell
• The cell cycle makes new cells

  1. Body cells in multicellular organisms (e.g. me, you or a plant)divide to make new cells. This is part of a series of stages called the cell cycle
  2. The stage of the cell cycle when the cell divides is called mitosis
  3. Multicellular organisms use mitosis to grow and develop
• Stages of cell cycle - Growth & DNA replication:

  Before it divides:

  1. The cell grows and increases the amount of subcellular structures such as ribosomes and mitochondria
  2. The DNA is replicated (copied) - so there's one copy for each new cell
  3. The DNA forms X-shaped chromosomes(The left arm has the same DNA as the right arm of the chromosome). Each 'arm' of the chromosome is an exact copy of the other
• Stages of cell cycle - Mitosis:

  The cell cycle is now ready for dividing...

  4. The chromosomes line up at the centre of the cell

  5. The two arms of each chromosome are pulled apart to opposite ends of the cell

  6. This divides the nucleus

  7. Each set of chromosomes become the nucleus of a new cell

  8. The cytoplasm and cell membrane divide

  9. The cell has now produced two new cells

  • They both contain the same DNA - they're identical
  • They're also identical to the original cell