DNA replication

• Why is DNA replication described as semi-conservative?


  Each new molecule is made up of one new and one old template strand
• State the function of DNA polymerase


  catalyses formation of phosphodiester bonds between DNA nucleotides
• State the function of DNA helicase


  Unzips DNA double helix, breaking hydrogen bonds
• What bonds do DNA/RNA polymerase catalyse?


  phosphodiester bonds
• The 2 strands of the double helix are .............. to eachother


  antiparallel
• Describe 2 reasons for DNA replication


  cell divison and reproduction
• Define what is meant by semi-conservative 


  as the 2 molecules of DNA created consist of one original strand and one newly synthesised strand
• How does the structure of DNA enable genetic conservation


  DNA is double stranded so each strand acts as a template to produce a new strand

  Hydrogen bonds are weak and easily break/form between complementary bases

  purines can only bind to a pyrimidine due to their different sizes and numbers of hydrogen bonds
• Describe the steps that happen in semi-conservative replication


  . DNA molecule unwinds

  . DNA helicase breaks hydrogen bonds between complementary base

  pairs so the DNA molecule unzips

  . each strand of the DNA molecules acts as a template strand

  . Free DNA nucleotides complementary base pair to exposed bases on

  the template strands

  . DNA polymerase forms phosphodiester bonds between adjacent nucleotides forming the sugar-phosphate backbone

  . Each DNA molecule formed contains one original strand and one new strand
• What type of effect does a mutation have on DNA?


  alter the sequences of amino acids in the protein causing an abnormal protein to be produced which could have either a positive or negative effect
• DNA helicase is present in both transcription and DNA replication, RNA polymerase is only present in transcription and DNA polymerase is only present in DNA replication
• Give evidence that DNA replication is semi-conservative

  • after 2 replications, 2 DNA molecules have one original and one new strand and 2 DNA molecules have 2 new strands
  • after 3 replications there are 8 DNA molecules, only 2 of which have strands from the original DNA
• phosphodiester bonds form between the monomers. They consist of a ..... group between the ...... molecules, forming the ...... of a molecule

  1 ) phosphate

  2 ) pentose

  3 ) strands
• Explain how pairing of nitrogenous bases allows identical copies of DNA to be made (3)

  • adenine pairs with thymine, guanine pairs with cytosine
  • because of hydrogen bonding
  • purines can only bind to pyramidines due to difference sizes
• Outline how the process of DNA replication is completed following the pairing of nitrogenous bases (3)

  • DNA polymerase joins the phosphodiester bonds between adjacent nucleotides
  • sugar-phosphate reforms
  • DNA rewinds into the double helix