biology topic 21

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  • Biology Topic 2
    • Fertillisation
      • Term used to describe when nuclei of female and male gametes fuse
      • For Animals
        • 1. Sperm swim towards the egg cell in the oviduct
          • 2. Once one sperm makes contact with the zona pellucida of the egg cell, the acrosome reaction occurs-This is where digestive enzymes are released from the acrosome of the sperm
            • 3. These enzymes digest the zona pellucida, so that the sperm can move through it to the cell membrane of the egg cell
              • 4. The sperm head fuses with the cell membrane of the egg cell. This triggers the cortical reaction- the egg cell releases from the contents of vesicles called cortical granules into the space between the cell membrane and the zona pellucida
                • 5. The chemicals from the cortical granules make the zona pellucida thicken, which makes it impenetrable to other sperm. This makes sure that only one sperm fertilises the egg cell
                  • 6. Only the sperm nucleus enters the egg cell- its tail is discarded
                    • 7. The nucleus of the sperm fuses with the nucleus of the egg cell-HAZAH FERTILISATION!
    • Cell differentiation
      • 1. Stem cells all contain the same genes, but not all of them are expressed because not all of them are active
        • 2. Under the right conditions, some genes are activated and other genes are inactivated
          • 3. mRNA is only transcribed from the active genes
            • 4. The mRNA from the active genes is then translated into proteins
              • 5. These proteins modify the cell-they determine the cell structure and control cell processes (including the activation of more genes, which produce more proteins)
                • 6. Changes to the cell produced by these proteins cause the cell to become specialized (differentiate). These changes are difficult to reverse, so once a cell has differentiated it stays specilaized
    • Stem cells
      • Cell differentiation
        • 1. Stem cells all contain the same genes, but not all of them are expressed because not all of them are active
          • 2. Under the right conditions, some genes are activated and other genes are inactivated
            • 3. mRNA is only transcribed from the active genes
              • 4. The mRNA from the active genes is then translated into proteins
                • 5. These proteins modify the cell-they determine the cell structure and control cell processes (including the activation of more genes, which produce more proteins)
                  • 6. Changes to the cell produced by these proteins cause the cell to become specialized (differentiate). These changes are difficult to reverse, so once a cell has differentiated it stays specilaized
      • Totipotency- the ability to produce all cell types, including all the specialised cells in an organism and extraembryonic cells (cells of the placenta and umbilical cord)
      • Pluoripotency- the ability of a stem cell to produce all specialized cells in an organism (but not extraembryonic cells)
      • Unspecialized cells that can develop into any type of cell
      • Medical uses
        • Stem cell therapies
          • Leukemia patients can have bone marrow transplants
          • Spinal cord injuries
          • Heart disease
            • Damaged caused by heart attacks
        • Save many lives
          • Donor organs restocked fully
        • Cure blindness-replaces old eye cells with cells created by newly formed eye cells
      • Sources
        • Adult stem cells
          • Found in bone marrow
          • Simple operation
          • Little risk involved
          • Not as flexible-Can only differentiate into a limited type of cells
        • Embryonic
        • Embryonic stem cells
          • Obtained from early embryos
            • Created in a laboratory using IVF
            • 4-5 days old stem cells are removed
            • Embryo is destroyed in process
          • Can differetiate into all cell types

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