DNA

• What are nucleic acids?

  • Carry genetic code
  • Determine order of amino acids
  • Two types: Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)
• The structure of nucleotides

  phosphate group, sugar, nitrogenous base
• Nitrogenous base

  • An organic base that contains nitrogen
  • purine: 2 rings, adenine and guanine
  • pyrimidine: 1 ring, thymine, cytosine and uracil (RNA)
• Polynucleotides

  • Very long chain of nucleotides
  • Joined by condensation reactions
  • Phosphodiester bonds
• Structure of DNA

  • 2 polynucleotide strands
  • Backbone is a sugar-phosphate arrangement
  • Bases project to the inside of the helix
  • Second polynucleotide chain runs in the opposite direction to the first
  • Strong, covalent, sugar-phosphate bonds
  • Hydrogen bonds hold bases together
  • Needs to be easy to split
  • Bases align in accordance to the base pairing rule
• Function of structure: phosphodiester bonds


  • keeps the DNA intact
  • stops it falling apart
• Function of structure: hydrogen bonds between bases


  • makes it easy to split DNA
  • allows and enables replication
• Function of structure: double stranded


  • 2 strands are complimentary
  • stabilises DNA
• Function of structure: long polymer


  • can store more genetic material
  • keeps genetic material in order
• Function of structure: helical coil


  • makes it easier to store in small spaces/ compact
• Function of structure: base pairs in the centre of helix


  • easiest way for the strands to bond
  • keeps the bases safe
• How is DNA adapted to its function?

  • sugar phosphate backbone lets DNA pass through generations
  • Double stranded= allows for semi conservative replication
  • 3.2 billion base pairs= infinite combinations= mass diversity
• What is RNA?

  • transfers genetic info from DNA to ribosomes
  • polynucleotide
  • single, short chain
  • contains ribose sugar instead of deoxyribose
  • A & U, C & G
• Types of RNA

  mRNA (messenger), tRNA (transfer), rRNA (ribosomal)
• mRNA

  • single strand copy of one gene
  • takes the gene to the ribosome, used for protein synthesis
• tRNA

  • single stranded molecule
  • folds using complimentary base pairs
  • Acceptor stem attaches to an amino acid
  • carries an amino acid to the ribosome to make it into a protein
  • Anticodon is complimentary to a mRNA codon
• rRNA

  • single stranded
  • folds using complimentary base pairing
  • forms part of the ribosomal structure
• The structure of RNA

  • pentose sugar is ribose NOT deoxyribose
  • RNA sugar has an extra oxygen on the second carbon
• RNA nucleotide

  
• Bases of RNA


  Thymine is replaced by uracil