Biology Topic 3

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  • Biology Topic 3
    • In the Beginning
      • Prokaryotic Cells
        • Extremely small (less then 2um diameter)
        • DNA is circular
        • No nucleus - DNA free in cytoplasm
        • Cell wall made of polysaccharides
        • Few organelles, no mitochrondria
        • Smaller ribosomes
      • Eurokaryotic Cells
        • Complex
        • Animal and plant cells
        • Larger cells (2-200um)
        • DNA linear
        • Nucleus present - DNA within
        • No cell wall (in animals, celluose wall in plants
        • Many organelles, mitochrondria present
        • Ribosomes present
      • Protein Transport
        • 1. Transcription of DNA to mRNA
        • 2. mRNA leaves nucleus
        • 4. Proteins move through the ER assuming 3D shape on route
        • 5. Vesicles rER fuse to form the flattenmed daces of the golgi appartus
        • 7. Proteins are modified within the golgi appartus
        • 3. Protein made on ribosomes enter the rER
        • 8. Vesicles pinch of golgi appartus containing modified proteins
        • 9. Vesicle fuses with surface membrane releasing protein
      • Gametes
        • Male and female sex cells that reproduce sexually
        • They join by fertilisation to form a zygote with 46 chromosomes
        • In plants, male gametes are pollen grains and female gamets are ovules
        • Contain half the number of chromosomes as normal body cells (23)
        • Sperm cells are composed of: nucleus, mitochrondria, flagellum, acrosome
        • Egg cells are composed of: cell membrane, follicle cells (which form a protective coat), a sona pellucida and a nucleus.
      • Meiosis
        • Happens in the reproductive organs to produce gametes
        • Cells that divide by meiosis have 46 chromosomes
        • Without meiosis, you'd get twice as many chromosomes at fertilisation
        • Overview of meiosis:
          • 1. DNA replicates to form two identical chromosomes called chromatids
          • 2. DNA condences to form double-armed chromosomes (made of chromatids)
          • 3. Chromosomes arrange into homologous pairs
          • 4. Homologous pairs are separated, halving the chromosome number
          • 5. Pairs of sister chromatids are separated
          • 6. Four new gametes are produced which are genetically identical
        • Why do we get genetic variation?
          • Crossing Over of Chromatids
            • 1. Homologous pairs come together and pair up
            • 2. Two of the chromatids in the pairs twist around each other
            • 3. The twisted bits break of and rejoin the othe chromatid instead, combining the genetic material
            • 4. Chromatids still contain the same genes. but different alleles
            • 5. Four new cells have been created, each containing different alleles
          • Independant Assortment of Chromosomes
            • 1. Four different daughter cells have different combinations of chromosomes
            • 2. Half of your chromosomes come from your Mum, and the other half from your Dad
            • 3. When gametes are produced, different combinations of these chromosomes go into cells
            • 4. This is called independant assortment of chromosomes
      • Fertilisation in Mammals
        • Exact moment when nuclei of male and female gamete fuse
        • The zygote that forms contains half the genetic material from mum and dad
        • Process of fertilisation in the Oviduct
          • 1. Sperm reach the ovum
          • 2. Chemicals are released from ovum to trigger acrosome reaction
          • 3. Acrosome swells, fusing with sperm cell surface membrane
          • 4. Digestove enzymes are released from acrosome
          • 5. These enqymes digest through the follicle cells
          • 6. The sperm fuses with the ovum membrane
          • 7. The sperm nucleus enters the ovum
          • 8. Enzymes from lysosome thicken jelly-like layers of egg preventing other sperms enters
          • 9. Nuclei of ovum and sperm fuse
      • Fertilisation in Flowering Plants
        • 1. Pollen grains grain on stigma of flower
        • 2. Pollen tube grows down the syle.  Three nuclei - two male gametes and one tube nucleus
        • 3. When the tube reaches the ovary, grows through the microphle and into the embryo sac
        • 4. The tube nucelus disintegrates, and tip of pollen tube bursts releasing two male gametes
        • 5. One male gamete fuses with egg nucleus (zygote formed)
        • 6. Second gamete fuses with polar nuclei and this acts as a food source
        • 7. Double fertilisation has occured
    • From one to many: the Cell Cycle
    • How development is controlled
    • Genes and Environment

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