B3 - A

  • Created by: zoolouise
  • Created on: 02-06-15 17:43
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  • Molecules of life
    • Cell structure
      • The number of mitochondria in a cell depend on the cell activity, this is because respiration occurs in mitochondria.
        • Mitochondria are found in the cytoplam
          • Liver cells have large numbers of mitochondria as it carries out many functions, muscle cells have many mitochondria as they need to contract.
      • Ribosomes are also found in the cytoplasm, they are smaller than mitochondria and can only be seen with an electron microscope.
        • Ribosomes are the site of protein synthesiss
    • DNA and the genetic code
      • The nucleus contains genes and each gene is a section of chromosome made of DNA, and it also cods for a particular protein.
      • DNA Is made of 2 strands coiled together to form a double helix.
        • Each strand contains chemicals called bases. There are also cross links between each strand formed by pairs of bases. Each gene contains a different sequence of bases.
      • The DNA base code controls what protein is made. The base sequence in DNA codes for the amino acid sequence in protein. 1 amino acid = 3 bases.
        • There are 4 types of bases. A-T, C-G. The cross links between strands are always between the same bases and this is called complementary base pairing.
      • Proteins are made in the cytoplasm but DNA can not leave the nucleus, therefore a copy of each gene is made which can leave the nucleus and carry the code to the cytoplasm.
      • The code needed to produce a protein is carried from DNA to the ribosomes by a molecule called mRNA.
    • Discovering the structure of DNA
      • Watson and Crick discovered the structure of DNA in 1953 but shared the nobel prize in 1962.
      • Watson and Crick used data from other scientists to build a model of DNA : They used xray photographs which showed DNA had 2 strands in a helix, they also used data indicating that bases occurred in pairs.




thank you

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