Question

Arrange the following steps of DNA replication in E. coli in a correct sequence: A. Formation of Okazaki fragments which are of 1000 to 2000 nucleotides B. Helicase unwinds the helix with the help of topoisomerase like DNA Gyrase C. DNA polymerase I or RNase H removes the RNA primer and polymerase I synthesizes complementary DNA to fill the gap D. A special RNA polymerase ‘primase' synthesizes a short RNA primer complementary to DNA E. Fragments are joined by the enzyme DNA ligase

• A. D, A, E, C, B
• B. A, C, D, E, B
• C. C, A, D, B, E
• D. B, D, A, C, E

Hint:

Remember: Unwind $\rightarrow$ Prime $\rightarrow$ Elongate $\rightarrow$ Remove primer $\rightarrow$ Ligate.

Answer 1

The Correct Option is D

Step 1: Concept
The sequential steps of DNA replication in E. coli.

Step 2: Meaning
DNA replication is a tightly ordered process: unwinding, priming, elongation, primer removal, and ligation.

Step 3: Analysis
B: Helicase (+ topoisomerase/gyrase) unwinds the double helix.
D: Primase synthesises short RNA primers.
A: DNA polymerase III elongates, forming Okazaki fragments (1000--2000 nt).
C: DNA polymerase I removes RNA primers and fills gaps with DNA.
E: DNA ligase seals the nicks to form a continuous strand.

Step 4: Conclusion
Correct sequence: B $\rightarrow$ D $\rightarrow$ A $\rightarrow$ C $\rightarrow$ E. Final Answer: (D)