Cell Control

• Multicellular eukaryotic organisms require a continuous supply of new cells for growth, development and repair
• Cell cycle


  1. Growth

  2. DNA replication

  3. Mitosis and division (cytokinesis)
• DNA


  Usually spread out in long strings, condenses into chromosomes when cell prepares for division
• Chromosomes


  • Packets of DNA, contain 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
• Chromosome duplication


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

  1. Chromosomes line up at cell center

  2. Fibers attach to each half of chromosomes and pull them to opposite sides of cell

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


  Cell membrane and cytoplasm pull apart, forming two daughter cells with identical DNA
• Body cells


  • Normally have two copies of each chromosome
• Cell division by mitosis

  1. Makes two cells identical to the original

  2. The nucleus of each new cell contains the same number of chromosomes as the original
• Cell cycle


  Makes new cells for growth and repair
• Cell division


  1. Body cells in multicellular organisms divide to produce new cells during a process called the cell cycle

  2. The stage of the cell cycle when the cell divides is called mitosis
• Mitosis


  • Multicellular organisms use it to grow or to replace cells that have been damaged
  • Some organisms use it to reproduce - this is called asexual reproduction
• Cell cycle stages


  1. Interphase

  2. Mitosis and Cytokinesis
• Interphase


  1. DNA is all spread out in long strings

  2. Cell grows and increases subcellular structures

  3. Cell duplicates its DNA - so there's one copy for each new cell

  4. DNA is copied and forms X-shaped chromosomes
• Mitosis


  1. Prophase - Chromosomes condense, membrane around nucleus breaks down

  2. Metaphase - Chromosomes line up at centre of cell

  3. Anaphase - Spindle fibres pull chromosomes apart, chromatids pulled to opposite ends

  4. Telophase - Membranes form around each set of chromosomes, cytoplasm and cell membrane divide to form two new cells
• At the end of mitosis, the cell has produced two new daughter cells, each containing the same sets of chromosomes as the other