A molecular biologist is setting up a polymerase chain reaction (PCR) to amplify a genomic DNA sequence. After running the thermocycler through 30 cycles of 95∘C→55∘C→72∘C95^\circ\text{C} \rightarrow 55^\circ\text{C} \rightarrow 72^\circ\text{C}95∘C→55∘C→72∘C, they find that no target DNA has been amplified. It is discovered that one key component was omitted from the reaction mixture.
Which of the following omissions would explain the complete absence of DNA amplification, along with the correct biological reason?
Omission of DNA ligase, because phosphodiester bonds cannot be formed to link the newly incorporated nucleotides together.
Omission of helicase, because the template strands cannot be unwound and separated at 55∘C55^\circ\text{C}55∘C to allow primer binding.
Omission of DNA primers, because Taq DNA polymerase requires a pre-existing 3′-OH3'\text{-OH}3′-OH group to initiate synthesis of the complementary strand.
Omission of RNA polymerase, because it is required to synthesize the primers needed for Taq polymerase to bind to the template.
