DNA structure

• formation of a polynucleotide 


  nucleotides monomers are joined with phosphodiester bonds forming polynucleotide = nucleic acid
• phosphpdiester bond 


  forms polynucleotide = nucleic bond

  OH on the 3Carbon reacts with the phosphate group attached to the 5Carbon on another nucleotide
• what direction is DNA synthesised

  5' to 3'
• two strands of DNA

  anti parallel
• the Watson-crick model of DNA structure

  DNA has a double stranded helical structure

  sugar phosphate backbone is on the outside

  bases inside

  stabilised by hydrogen bonds
• what does the model provide

  a stimulus for deciphering the genetic code

  possible mechanism for replication of DNA
• what kind of replication

  semi-conservative
• what is needed to make a DNA copy

  unwinding of helical double stranded DNA (two parental templates)

  prevention of unwound double-stranded helical DNA

  joining of ends of newly synthesised fragments together (lagging and leading strands)
• leading strand 


  continuously synthesised in 5' to 3' direction
• lagging strand 


  discontinuously synthesised in the 5' to 3' direction as Okazaki fragments
• replication, semi-discontinuous 


  bidirectional

  
• primase 


  an enzyme (type of RNA polymerase) RNA primer = starting point for DNA polymerisation
• DNA polymerase III


  needs an OH group on the phosphate group of the incoming nucleotide

  only makes DNA in the 5' to 3' direction

  synthesises a new DNA strand by adding nucleotides complementary to the parental templates
• DNA polymerase I 


  removes RNA primers

  fills the gap with DNA nucleotides (DNA polymerase)
• DNA ligase 


  joins newly synthesised Okazaki fragments together. creates phosphodiester bonds

  
• single- stranded DNA binding protein

  prevention of unwound double-stranded helical DNA, protect it from degradation
• topoisomerase 


  release of tension generated by unwinding the DNA helix
• Exonuclease 


  during replication DNA errors can be repaired

  DNA pol III has a proofing mechanism
• how are incorrect bases removed

  3' to 5' exonuclease by DNA pol III
• Endonuclease 


  after replication

  can be due to radiation damage and chemical modifications of bases
• Polymerase chain reaction (PCR)

  molecular photocopying
• how does PCR work

  Denaturing

  Annealing

  Extension
• where can PCR be used

  medical applications

  forensic applications

  infectious disease detection and identification

  molecular biology research
• what does PCR copy

  only targeted DNA will be copied