Revision Questions : Polymerase Chain Reaction

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Question 1: Which of the following can be amplified by PCR?
  • (1) RNA
  • (2) Single stranded DNA
  • (3) Double stranded DNA
  • INCORRECT! RNA is converted to DNA by reverse transcriptase for PCR
  • INCORRECT! Not just this.
  • CORRECT! Both single stranded and double stranded DNA can be amplified
  • INCORRECT! RNA is converted to DNA by reverse transcriptase for PCR
Question 2: If there is 1 copy of target gene before the PCR cycle starts, after 35th cycle, how many copies of target gene are there?
  • INCORRECT! After each cycle, the PCR product can act as template for further amplification
  • INCORRECT! After each cycle, the PCR product can act as template for further amplification
  • INCORRECT! Please try again!
  • CORRECT!
Question 3: The reason of using Taq polymerase in PCR is/are:
  • (1) It will not be denatured at 95oC.
  • (2) It can catalyze the polymerization process at 95oC.
  • (3) It adds nucleotides to the 3' end of each primer attaching to the DNA strand.
  • INCORRECT! There is still one important property of Taq polymerase
  • INCORRECT! Taq polymerase has limited catalytic function at 95oC
  • CORRECT!
  • INCORRECT! Taq polymerase temporarily stops working at 95oC and it works optimally at 72oC
Question 4: Which of the following CANNOT be used as a source of DNA for PCR?
  • INCORRECT! DNA in a single sperm can be amplified by PCR
  • INCORRECT! DNA in dried corncob had been successfully amplified by PCR
  • INCORRECT! Pulp tissue extracted from teeth can be used as a source of DNA
  • CORRECT! A very small quantity or even partly degraded DNA can be amplified by PCR
Question 5: The efficiency of PCR drops after several runs, this is because
  • (1) not all DNA are denatured as the DNA concentration becomes high.
  • (2) there are less nucleotides available.
  • (3) there is insufficient amount of active Taq polymerase.
  • INCORRECT! There are still other reasons
  • INCORRECT! There are still other reasons
  • INCORRECT! There are still other reasons
  • CORRECT! Taq polymerase has half life of 45 minutes at 94oC, so some Taq polymerase may be inactive.