Question

Circular plasmids are typically found in which form inside a bacterial cell?

1. Covalently closed circular
2. Open circular
3. Linear
4. Negatively supercoiled
5. More than one but not all of the above

Answer 1

The plasmids are generally in covalently closed circular form inside the bacterial cell and are negatively supercoiled.

Negative supercoiling means left -handed coiling of DNA, so the unwinding of DNA occurs in anticlockwise direction.

Both prokaryotes and eukaryotes have negatively supercoiled DNA. Negative supercoiling is beneficial because this prepares the DNA molecule for those processes that requires separation of DNA strands like transcription and replication.

And most bacterial DNA are circular because for this reason plasmids can copy themselves independent of the bacterial chromosome.

So, here option (E) is correct.