[Campbell Biology P.375] Which of the following sequences accurately describes the synthesis... | Practice Question

Which of the following sequences accurately describes the synthesis and processing of a single Okazaki fragment on the lagging strand during DNA replication, as depicted in Figure 16.18?

  • A: Primase synthesizes RNA primer → DNA pol III extends DNA → DNA pol I removes RNA primer and replaces with DNA → DNA ligase joins fragments.
  • B: DNA pol III synthesizes DNA → Primase adds primer → DNA ligase joins fragments → DNA pol I removes primer.
  • C: Helicase unwinds DNA → Primase synthesizes RNA primer → DNA pol I removes primer → DNA pol III extends DNA.
  • D: DNA pol I adds nucleotides → DNA pol III removes primer → DNA ligase seals nicks → Primase initiates synthesis.

Explanation

The synthesis of an Okazaki fragment on the lagging strand begins with primase synthesizing a short RNA primer. DNA polymerase III then extends this primer by adding DNA nucleotides. Subsequently, DNA polymerase I removes the RNA primer and replaces it with DNA nucleotides. Finally, DNA ligase forms a phosphodiester bond to join the newly synthesized DNA segment to the preceding Okazaki fragment, sealing the nick.