Cell cycle

• 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 condensed DNA
  • Each chromosome contains 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 chromosomes total
• Animals of different species can't reproduce to have fertile offspring due to different numbers of chromosomes
• Chromosome duplication


  Duplicate stays attached to original chromosome, forming an X shape
• Chromosome alignment


  1. Chromosomes line up along center of cell

  2. Fibers from either side attach to respective halves of chromosomes

  3. Chromosomes split in half into two separate arms
• Cell division (cytokinesis)


  1. Cell membrane and cytoplasm pull apart, forming two daughter cells

  2. Each daughter cell has identical DNA to parent cell
• Daughter cells can then contribute to growth, development or repair and undergo the cell cycle again