DNA and RNA

DNA and RNA

Nucleic Acids
1. there are 2 forms: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
  1. DNA
    1. Found in the Nucleus in a Eukaryotic cell where it acts as an information store.
  2. RNA
    1. Found in 3 different forms that are used to read and translate the information to produce various proteins that are required to function.
2. The monomer of all Nucleic Acids is called a Nucleotide
  1. The Nucleotide is made up of 3 sub units: A phosphate group, a sugar molecule and a Nitrogenous Base.
    1. Joined by Covalent Bonds
    2. There are 4 different Nucleotides, that have the same Phophate group, either deoxyribose sugar or ribose sugar and one of four different Nitrogenous bases.
      1. Adenine, Guanine, Cytosine, Thymine (Thymine isn't present in RNA so is replaced with Uracil)
  2. Joining Nucleotides together.
    1. Condensation Reaction between the Phosphate group of one Nucleotide and the sugar of another Nucleotide.
      1. Repeating this reaction gives a long chain of Nucleotides.
        Forms a Sugar-Phosphate backbone.
  3. The Organic Nitrogenous Bases are grouped into either Purines or Pyrimidines.
    1. Adenine and Guanine are Purines.
      1. 2 Ring Structure
    2. Thymine, Uracil and Cytosine are Pyrimidines.
      1. 1 Ring Structure
      2. Pyrimidines are smaller than Purines.
3. Too much Nucleic Acid causes Gout
  1. Uric acid is produced when excess Purines are broken down in the liver. It is then excreted in the Urine.
    1. Some people have too much Uric acid in their blood. Uric acid is insoluble at lower temperatures and forms crystals that are deposited in the joints at the extremities such as the toes. The toe joint becomes very painful and swollen- a condition called Gout.
DNA
1. DNA is a long-chain polymer of nucleotide monomers. The polymer is called a polynucleotide. A DNA molecules forms when 2 polynucleotide strands come together forming what looks like a ladder.
  1. Hydrogen bonds form between the bases to strengthen the rungs of the ladder. This gives DNA a very stable structure which is vital as it carries the instructions to make an organism. If it were unstable the instructions could go wrong to easily.
2. The 2 DNA strand run parallel to each other and the space between them is taken up by the Nitrogenous bases projecting inwards. The term 'Antiparallel is used because the strands run in opposite directions to each other - the sugars are pointing in opposite directions.
  1. The bases pair up in a specific way which keeps the chains the same distance apart.
    1. When a pyrimidine appears on one side a purine will appear on the other.
      1. Adenine pairs with Thymine (or Uracil in RNA)
      2. Guanine pairs with Cytosine
      3. As the pairs come together, Hydrogen bonds form between the bases.
      4. Base Pairing is described as Complementary.
3. Making Copies of DNA
  1. When a cell divides each new cell much receive a full set of instructions. Each cell must have a full copy of all the DNA for that organism.
  2. DNA replication takes place during the Interphase of the Cell Cycle.
  3. 1) DNA helix is untwisted.
    1. 2) Helix unzips by the use of the enzyme HELECASE.
      1. 3) The original DNA strand acts a template for the new RNA strand.
        4) Free floating DNA Nucleotides bond to the exposed bases by complementary base pairing rules.
        5) Semi-Conservative Replication
        6) Protein synthesis. The Hydrogen bonds break and the RNA is now called mRNA which goes into the Ribosomes.
        7) Primer signals tRNA to collect the Amino Acids and transport them to the Ribosomes.
        8) RNA Polymerase is the enzyme that allows the Amino Acids to bond together by the RNA code.
4. Structure and function in DNA
  1. The sequence of bases is an example of information storage because the information is in the form of codes that are used to build Proteins.
  2. The molecules are long so a large amount of information can be stored.
  3. The base-pairing rules means that the complementary strand of information can be replicated.
  4. The Double Helix structure gives the molecule stability.
  5. Hydrogen Bonds allow easy unzipping for copying and reading information.
RNA
1. Important structural differances between DNA and RNA.
  1. The sugar molecule is Ribose.
  2. Contains the Nitrogenous Base Uracil instead of Thymine.
  3. The poly-nucleotide chain is usually single stranded.
  4. 3 forms of RNA molecule exist.
2. 3 forms of RNA.
  1. mRNA ( messenger RNA)
    1. A strand that is complementary to a strand of DNA (the template strand) it is therefore a copy of the other DNA strand (the coding strand) of the double helix.
  2. tRNA (transfer RNA)
    1. Carries Amino Acids to the Ribosomes where they are bonded together to form Polypeptides.
  3. rRNA (ribosomal RNA)
    1. Found in the Ribosomes.
Scientists.
1. In 1953 at Cambridge, James Watson and Francis Crick discovered the structure of DNA and worked out how it might form the instructions for life.
  1. Their work and the key moment of discovery owed much work that was done by at the same time by Rosalind Franklin, Raymond Gosling and Maurice Wilkins at Kings College London.
    1. The x-ray patterns they produced using DNA crystals enabled Watson and Crick to finally piece together a full model of the structure of SNA that also explained how copies might be made from it.

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