1.2 Replication of DNA

• Describe the purpose of DNA replication.

  Ensures that the daughter cells will have a full chromosome complement after mitosis
• state what a primer is and explain its function during DNA replication.

  A short strand of nucleotides which bind to the 3’ end of the template strand.

  Acts as a start point for DNA polymeras.
• Explain why DNA polymerase is required for DNA replication.

  Adds nucleotides to the 3’ end of a growing DNA strand. Creates the strong chemical bonds to create the sugar phosphate backbone.
• Explain why Ligase is needed for DNA replication.

  An enzyme that joins DNA fragments together on the lagging strand.
• Explain why only the leading strand can be synthesised continuously.

  DNA polymerase can only add to the 3’ end.
• Describe the purpose of polymerase chain reaction (PCR)


  Amplifies target sequences of DNA.
• Give the temperature range and describe what is happening during stage 1 of PCR.

  92°-98°

  strands are separating as hydrogen bonds are being broken.
• Give the temperature range and describe what is happening during stage 2 of PCR.

  50°-65°

  Primers bind to target sequences
• Give the temperature range and describe what is happening during stage 3 of PCR.

  70°-80°

  Heat tolerant DNA polymerase replicates region of DNA.
• State two practical applications of PCR.

  Solve crimes.

  Settle paternity suits.
• What are primers?


  Short strands of nucleotides
• What must happen for DNA polymerase to start replication?

  A primer must bind to the 3' end of the template DNA.
• The lagging strand is...


  Replicates in fragments (discontinuously).
• Why is ATP required for the replication of DNA?

  Provides energy for nucleotides to be added to the new strand.
• What is the purpose of the template DNA strand?

  Provides the correct base sequence to be replicated.
• What is the purpose of free DNA nucleotides?

  Join onto the exposed template strand allowing synthesis of the new DNA strand.
• Why does PCR use heat tolerant DNA polymerase?


  Ensures that the enzyme does not denature during the repeated heating and cooling.
• In PCR, what does the repeated cycles of heating and cooling allow?

  Allows the target sequences to be amplified in a shorter time, making the process more efficient.