Review Question - QID 106556

The siRNA will destroy the helicase mRNA transcript resulting in no helicase protein expression. In the absence of helicase, DNA will not be unwound and no replication can occur.

DNA replication begins with helicase unwinding the DNA and separating the two strands of DNA. To prevent the strands from reannealing, single stranded binding proteins (SSBs) stabilize the individual strands. RNA primase then creates an RNA primer to allow for DNA polymerase III to begin creating newly synthesized DNA. As replication continues, supercoiling is created in which case topoisomerase II relieves this tension. Finally, DNA polymerase I removes and replaces the primer of the next fragments, and the two fragments are sealed by DNA ligase. The these last two steps are only involved in the lagging strand.

Incorrect Answers:
Answer 2: Topoisomerase is involved in relieving both positive and negative supercoiling that occurs during DNA replication. If topoisomerase is knocked down, the supercoiling will not be relieved and DNA will not be able to be unwound further.
Answer 3: Single stranded binding proteins (SSBs) bind and stabilize melted DNA after they have been unwound by helicase. If SSBs are knocked down, then the two melted DNA strand reanneal.
Answer 4: Primase is involved in creating a primer in which DNA polymerase uses as a starting point to synthesize new DNA. If primase is knocked down, then no primer will be created.
Answer 5: Ligase is responsible for ligating fragment of newly replicated DNA. If ligase is knocked down, then the fragments will not be ligated.