Question

As per the general model, the order of the activities in the DNA replication in E coli from the beginning to the end is:
A. Enzyme ‘primase’ synthesizes the ‘primer RNA’
B. Single-strand binding (SSB) proteins bind to the separated single strands and stabilize them.
C. DNA gyrase and DNA helicase unwind the complementary strands of DNA in the origin of replication (Ori C).
D. After digesting the RNA primers, the ‘Okazaki fragments' are joined together by the enzyme ‘ligase’.
E. Synthesis of DNA starts and goes continuously in the ‘leading strand’ and discontinuously in the ‘lagging strand’
Choose the correct answer from the options given below:

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

Hint:

To easily solve replication sequencing questions, remember that unwinding (C) must happen first to allow proteins to bind, and joining of fragments by ligase (D) is always the final step.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
DNA replication in prokaryotes like E. coli is a multi-step biological process carried out by an enzyme complex. It proceeds in a highly coordinated, sequential order.

Step 2: Detailed Explanation:
Let us arrange the steps of replication chronologically:
1. Unwinding (C): Replication begins at the unique origin site (oriC). DNA gyrase relieves topological tension, and DNA helicase unwinds and separates the double-stranded DNA.
2. Stabilization (B): Single-strand binding (SSB) proteins rapidly bind to the exposed single strands to prevent them from re-annealing and to protect them from degradation.
3. Priming (A): DNA polymerases cannot synthesize DNA de novo and require a free 3'-OH end. The enzyme primase synthesizes short RNA primers complementary to the DNA template.
4. Elongation (E): DNA Polymerase III extends the primers, synthesizing DNA continuously on the leading strand and discontinuously as Okazaki fragments on the lagging strand.
5. Ligation (D): DNA Polymerase I removes the RNA primers and fills the gaps with DNA. Finally, DNA ligase joins the adjacent Okazaki fragments covalently.
The sequential order of these events is C, B, A, E, D.

Step 3: Final Answer:
Hence, the correct sequence is C, B, A, E, D.