DNA and RNA

• DNA stands for deoxyribonucleic acid
• RNA stands for ribonucleic acid
• DNAs function is to store genetic information
• RNAs function is to transfer genetic information from DNA to ribosomes
• nucleotides are made of:

  • a phosphate group
  • a pentose sugar
  • a nitrogenous base
• nucleotides join via condensation reactions between the phosphate group of one nucleotide and the sugar of another. this forms a phosphodiester bond
• DNA has a double helix structure
• RNA is single stranded
• the four nitrogenous bases in DNA are:

  • A - adenine
  • T - thymine
  • G - guanine
  • C - cytosine
• in RNA, uracil pairs with adenine instead of thymine
• DNA contains a deoxyribose sugar whereas RNA contains a ribose sugar
• complimentary bases join by hydrogen bonding
• there are two hydrogen bonds between adenine and thymine/uracil
• there are three hydrogen bonds between guanine and cytosine
• polynucleotide stands are antiparallel - they run in opposite directions
• RNA is usually shorter than DNA
• cytosine, thymine and uracil are prymidines - single rings
• adenine and guanine are purines - double rings
• stages of DNA replication

  • DNA helicase breaks hydrogen bonds between bases
  • original stand acts as a template for free floating nucleotides to join to their complimentary bases by hydrogen bonding
  • DNA polymerase catalyses condesation reactions to form sugar phosphate backbone
• DNA polymerase always builds the new stand in the 5’ to 3’ direction. This means it moves along the strand in the 3’ to 5’ direction
• The two main isotopes of nitrogen are nitrogen 14 and nitrogen 15
• to test for semi conservative replication bacteria that were grown in heavy nitrogen were taken and placed in broth containing light nitrogen and left for one replication. when the sample was spun in a centrifuge the DNA settled in the middle showing it contained one strand of nitrogen 14 and one of nitrogen 15