Question

What types of DNA molecules are copied using rolling circle replication process?

• A. Bacterial chromosomes
• B. Some bacteriophage genomes (such as $\lambda$)
• C. Mitochondrial genome
• D. Yeast chromosomes

Hint:

Rolling circle replication (RCR) is a unidirectional mechanism used by circular plasmids and bacteriophages (like $\lambda$ and $\Phi X174$) to synthesize long, concatemic genomic repeats.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Rolling circle replication (RCR) is a process of unidirectional nucleic acid replication that can rapidly synthesize multiple copies of circular molecules of DNA or RNA.
This mechanism is widely used by circular genetic elements, including plasmids, some eukaryotic viruses, and several bacteriophages.

Step 2: Detailed Explanation:
Rolling circle replication begins when a site-specific nick is made by an initiator protein in one strand of a double-stranded circular DNA molecule, exposing a free 3'-hydroxyl ($\text{OH}$) end and a 5'-phosphate ($\text{P}$) end.
DNA polymerase uses the intact, un-nicked circular strand as a template to elongate the 3'-OH end, displacing the 5'-terminated single strand as it replicates around the circle.
This continuous synthesis yields a long, single-stranded concatemer consisting of multiple tandem repeats of the genome.
This mechanism is utilized during the lytic cycle of certain bacteriophages, such as bacteriophage $\lambda$ and $\Phi X174$, to generate the concatemic DNA molecules that are subsequently packaged into viral heads.
In contrast, bacterial chromosomes replicate via a bidirectional, theta-type mechanism originating from a single origin ($\textit{oriC}$).
Yeast chromosomes and mitochondrial genomes also use distinct bidirectional replication systems rather than the rolling circle mechanism.

Step 3: Final Answer:
Rolling circle replication is used to copy some bacteriophage genomes (such as $\lambda$), which corresponds to Option (B).