Cell division

• Cell


  The basic unit of life
• Chromosomes


  • Made of DNA
  • Found in pairs (one from father, one from mother)
• Cell division


  A type of cell division required for growth and repair
• The Cell Cycle


  1. Interphase

  2. Mitosis
• Mitosis


  • DNA replication
  • Production of more cellular structures
  • One set of chromosomes pulled to each end of the cell
  • Nucleus divides
• Stem cells


  Undifferentiated cells that can divide to give rise to many more cells of the same type, and from which other cells can arise through differentiation
• Stem cells from meristems in plants


  • Can be used to produce clones of plants quickly and economically
  • Can be used to protect rare species from extinction
  • Can be used to produce large numbers of identical plants with special features for farmers
• Embryonic stem cells


  Cells from an embryo that can divide and differentiate into the many different types of specialised cells required in the body
• Uses of embryonic stem cells


  • Can be used to treat medical conditions and diseases like type 1 diabetes, spinal cord or brain injury
  • Potential risks include transfer of viral infection and ethical/religious objections
• Therapeutic cloning


  Producing an embryo with the same genes as the patient, so stem cells from the embryo are not rejected by the patient's body and can be used for medical treatment
• Chromosomes


  Contain genetic information
• Chromosomes


  • Coded up lengths of DNA molecules
  • Each chromosome carries a large number of genes that control the development of different characteristics
  • Body cells normally have two copies of each chromosome - one from the mother and one from the father
• human cells contain 23 pairs of chromosomes and 46 all together
• Cell cycle

  Series of stages that body cells go through to divide and produce new cells for growth, development and repair
• Mitosis


  The stage of the cell cycle when the cell divides
• Cell cycle


  1. Growth & DNA replication

  2. Mitosis
• Growth & DNA replication

  • DNA is spread out in long strings
  • Cell grows and increases subcellular structures
  • DNA is duplicated to form X-shaped chromosomes with identical arms
• Mitosis


  1. Chromosomes line up at the centre of the cell

  2. Cell fibres pull the chromosomes apart

  3. Membranes form around the sets of chromosomes to become the nuclei of the two new cells

  4. Cytoplasm and cell membrane divide to produce two new daughter cells
• Stem cells


  Undifferentiated cells that can divide to produce lots of identical undifferentiated cells and differentiate into different cell types
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
• Embryonic stem cells


  • Can turn into any type of cell
  • Found in early humans
• Adult stem cells


  • Only found in certain places like bone marrow
  • Can only differentiate into certain cell types, not any cell type
• Stem cells from embryos and bone marrow can be grown in a lab to produce clones and differentiate into specialised cells for medicine or research
• Medicine already uses adult stem cells to cure disease, e.g. transferring stem cells from bone marrow to replace faulty blood cells
• Embryonic stem cells could be used to replace faulty cells in sick people, e.g. insulin-producing cells for diabetes, nerve cells for spinal injuries
• Therapeutic cloning


  Making an embryo with the same genetic information as the patient so the stem cells produced wouldn't be rejected
• There are risks involved in using stem cells in medicine, e.g. stem cells grown in the lab could become contaminated with a virus
• Arguments against stem cell research


  • Embryos are potential human lives and shouldn't be used for experiments
  • Curing existing patients is more important than the rights of embryos
  • Embryos used are usually unwanted ones from fertility clinics that would be destroyed anyway
  • Scientists should focus on finding other sources of stem cells instead
• In some countries, stem cell research is banned, but it is allowed in the UK as long as it follows strict guidelines
• Plant stem cells


  • Found in the meristems (parts of the plant where growth occurs)
  • Can differentiate into any type of plant cell throughout the plant's life
  • Can be used to produce clones of whole plants quickly and cheaply
  • Can be used to grow crops of identical plants with desired features like disease resistance