Cell division

• The nucleus of a cell contains chromosomes. Each chromosome carries a large number of genes made of DNA molecules
• Diagram of stuff

  
• Body cells divide to form two identical daughter cells by going through a series of stages known as the cell cycle. Cell division by mitosis is important for the growth and repair of cells, for example the replacement of skin cells. Mitosis is also used to asexual reproduction
• The three main stages of the cell cycle:

  • Stage 1 - cell grows bigger, DNA replicates (chromosomes are duplicated), increase in number of sub-cellular structures e.g ribosomes
  • Stage 2 - (mitosis) a complete set of chromosomes is pulled to each end of the cell, the nucleus divides to form two nuclei
  • Stage 3 - cytoplasm and cell membrane divide to form two identical daughter cells
• Stem cells are undifferentiated cells that can develop into one or more types of specialised cell. There are two types of stem cells in mammals, adult stem cells and embryonic stem cells. Stem cells can be cloned to produce large numbers of identical cells
• Adult stem cells:

  • Found in specific parts of the body in adult and children, e.g bone marrow
  • Can only differentiate to form certain types of cells, for example stem cells from bone marrow can only differentiate to form types of blood cells
  • Advantages - fewer ethical issues, adults can consent to have their stem cells removed and used. An already established technique to treat diseases like leukaemia. Relatively safe to use as a treatment and donors recover quickly
  • Disadvantages - requires a donor, potentially meaning a long wait time to find someone suitable. Can only differentiate to form certain types of specialised cells, so can be used to treat fewer diseases
• Embryonic stem cells:

  • Early human embryos often taken from spare embryos from fertility clinics
  • Can differentiate into any type of specialised cell in the body
  • Advantages - can treat a wide range of diseases as can form any specialised cell. May be possible to grow whole replacement organs. Usually no donor needed as they are obtained from spare embryos from fertility clinics
  • Disadvantages - ethical issues as the embryo is destroyed and each embryo is a potential human life. Risk of transferring viral infections to the patient. Newer treatment so relatively under researched, not yet clear if it can cure as many diseases as thought
• Plant meristem:

  • Found in meristem regions in the roots and shoots of plants
  • Can differentiate into all cell types - they can be used to create clones of whole plants
  • Advantages - rare species of plants can be cloned to prevent extinction. Plants with desirable traits such as disease resistance can be cloned to produce large numbers of identical plants. Fast and low cost production of large numbers of plants
  • Disadvantages - cloned plants are genetically identical, so a whole crop is at risk of being destroyed by a single disease or genetic defect
• In therapeutic cloning, cells from a patient’s own body are used to create a cloned early embryo of themselves. Stem cells from this embryo can be used for medical treatments and growing new organs. These stem cells have the same genes as the patient so are less likely to be rejected when transplanted