Nucleic acids

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Nucleotides and Nucleic Acids

  • Carbon, Hydrogen, Oxygen, Nitrogen and Phosphorus.
  • Large polymers formed from many nucleotides linked together in a chain.
  • Made of three components: a pentose monosaccharide (sugar) containing 5 carbon atoms, a phosphate group (inorganic and negatively charged), and a nitrogenous base (two carbon rings in its structure as well as nitrogen.
  • Linked by condensation reaction to form a polynucleotide.
  • Phosphodiester bonds are formed to create a sugarphosphate backbone with a base attached to each sugar.
  • Bonds broken by hydrolysis, releasing individual nucleotides.
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Deoxyribonucleic Acid (DNA)

  • Deoxyribose sugar.
  • Fewer oxygens than in ribose (deoxyribose has 4, ribose has 5).
  • 4 different bases - Thymine, Adenine, Cytosine and Guanine.
  • T and C are pyramidine.
  • A and G are Purine.
  • A and T pair and C and G pair.
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The Double Helix

  • DNA is made up of two strands of polynucleotides known as a double helix.
  • Held together by hydrogen bonds between the bases.
  • Each strand has a phosphate group at the 5' end and a hydroxyl group at the 3' end.
  • They run antiparallel.
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Base Pairing Rules

  • A and T form two hydrogen bonds.
  • C and G form three hydrogen bonds.
  • This is known as complementary base pairing.
  • A small pyramidine always binds to a large purine.
  • Mainains a constant dustance between the DNA backbones.
  • Watson and Crick determined the structure of the double helix in 1953.
  • Sequence of bases along the DNA strand that carries the genetic information in the form of a code.
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Ribonucleic Acid (RNA)

  • Transfer of genetic information from DNA to the proteins that make up enzymes and tissues of the body.
  • As DNA is a very long molecule, it is unable to leave the nucleus to supply protein synthesis.
  • To solve this problem, a relatively small section of the long DNA molecule is transcribed into a mRNA . 
  • mRNA is a polymer composed of many nucleotide monomers.
  • RNA is different to DNA because the pentose sugar is Ribose insetad of Deoxyribose.
  • In RNA, the thymine is replaced with Uracil - there are still two hydrogen bonds.
  • RNA molecules form polymers bythe formation of phosphodiester bonds in condensation reactions.
  • These polymers are small enough to leave the nucleus.
  • After protein synthesis, RNA molecules are degraded in the cytoplasm.
  • Phosphodiester bonds are hydrolysed and the RNA nucleotides are released and reused.
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