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MCAT Question A Day - 2/28/14 - Answer!

Which of the following shows the correct sequential order of enzymes active during DNA replication on the lagging strand?

A.  DNA helicase, DNA polymerase, DNA ligase, RNA polymerase
B.  DNA helicase, RNA polymerase, DNA polymerase, DNA ligase
C.  RNA polymerase, DNA helicase, DNA polymerase, DNA ligase
D.  RNA polymerase, DNA polymerase, DNA ligase, DNA helicase

The correct answer is (B). The DNA helicase partially unwinds the DNA double helix. RNA polymerase (primase) then synthesizes the primer to which DNA polymerase binds. DNA polymerase adds DNA nucleotides (5' to 3') to each okazaki fragment. DNA ligase then joins the fragments together.

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