cell processes

• 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 DNA containing a large number of genes that control the development of different characteristics
  • Eukaryotic cells have two copies of each chromosome, one from each parent
• 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
• Chromosome alignment and separation

  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 of the cell, breaking the chromosomes in half
• Cell division (cytokinesis)


  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
• Meiosis


  The process that forms gametes (sex cells)
• Gametes


  Cells that only contain half the genetic material of a normal cell (haploid)
• Diploid cells


  Cells that have two sets of genetic information, one from each parent
• Meiosis


  1. Replicate DNA

  2. Chromosomes line up in pairs

  3. Chromosome pairs pulled apart

  4. Cell splits in two

  5. Cell splits in two again
• Chromosomes


  • Contain genetic information
  • Humans have 23 different types
  • Each type has two copies, one from each parent
• The left-to-right order of chromosome pairs is random during meiosis
• The DNA in each of the four gametes produced by meiosis is genetically unique
• Sperm and egg fuse during fertilization

  Form a diploid cell that can divide by mitosis
• The diploid cell can divide by mitosis to form an embryo, fetus, and fully grown organism