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


  When a cell is not dividing, it is spread out in long strings; when preparing for division, it condenses into chromosomes
• Chromosomes


  • Packets of condensed DNA
  • Each chromosome contains a large number of genes that control the development of different characteristics
• Eukaryotic cells have two copies of each chromosome, one from the mother and one from the father
• Humans have 23 pairs of chromosomes, for a total of 46 chromosomes
• Chromosome duplication


  Each chromosome duplicates, with the duplicate staying attached to the original chromosome, forming an X shape
• Cell division


  1. Chromosomes line up at the center of the cell

  2. Fibers from either side of the cell attach to the respective halves of each chromosome and pull them to opposite sides

  3. Cell membrane and cytoplasm pull apart, forming two daughter cells with identical DNA
• The resulting daughter cells can then contribute to growth, development or repair and undergo the cell cycle all over again