Living and Growing B3 OCR Gateway

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  • Living and Growing B3
    • Cells
      • Animal cell Structure
        • Nucleus-Contains DNA in the form of chromosomes
        • Ribosome- Where proteins are synthesised.
      • Bacterial Cell Structure
        • Bacteria dont have chloroplasts or mitochondria
        • Cell membrane
        • Cell wall
    • DNA
      • Chromosomes are made of DNA
        • Chromosomes are long molecules of coiled up DNA. The DNA id divided up into short sections called genes.
          • Each nucleotide contains a small molecule called a ''base''. DNA has four different bases
            • Each base forms cross links to a base on the other strand. This keeps the two DNA strands tightly wound toghether.
            • A always pairs up with T, and C always pairs up with G. This is called complementary base pairing.
        • DNA is a double helix. Each of the two DNA strands is made up of lots of small groups called ''nucleotides''.
          • You only need to know the four bases by their first initials - A,C,G and T.
      • Watson and Crick
        • Scientists struggled for decades to work out the structure of DNA.
          • They used data from other scientists to help them understand the structure of the molecule. This included: X-ray data showing that DNA is a double helix formed two chains wound together. Other data showing that bases occurred in pairs.
      • DNA can replicate itself.
        • In order to copy itself, the DNA double helix first 'unzips' - to form two single strands.
          • The result is two double-stranded molecules of DNA that are identical to the original molecule of DNA.
        • New nucleotides then join on using complemantary base-pairing. This makes an exact copy of the DNA on the other strand.


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