Mitosis

• Multicellular eukaryotic organisms require a continuous supply of new cells for growth, development and repair
• The process through which these cells are generated is known as the cell cycle
• Cell cycle


  1. Growth

  2. DNA replication

  3. Mitosis and division (cytokinesis)
• DNA


  Usually spread out in long strings when cell is not dividing, condenses into chromosomes when cell starts to prepare for division
• Chromosomes


  • Packets of DNA, each containing a large number of genes that control development of different characteristics
  • Eukaryotic cells have two copies of each chromosome, one from mother and one from father
• Humans have 23 pairs of chromosomes, 46 in total
• Animals of different species can't reproduce to have fertile offspring due to different numbers of chromosomes
• Chromosome duplication


  1. Duplicate stays attached to original chromosome, forming an X shape

  2. Right half of each chromosome is a duplicate of the left half
• Chromosome alignment and separation


  1. Chromosomes line up along center of cell

  2. Fibers from either side attach to respective half of each chromosome and pull them to opposite sides of the cell, breaking the chromosomes in half
• Cell division (cytokinesis)


  Cell membrane and cytoplasm pull apart, forming two daughter cells with identical DNA
• Resulting daughter cells can then contribute to growth, development or repair and undergo the cell cycle all over again
• Prophase: Chromatin into chromosomes, the nuclear envelope break down, chromosomes attach to spindle fibres by their centromeres.
• 2) Metaphase: Chromosomes line up along the metaphase plate (centre of the cell).
• 3) Anaphase: Sister chromatids are pulled to opposite poles of the cell.
• 4) Telophase: Nuclear envelope reforms, chromosomes unfold into chromatin, cytokinesis can begin.