Question

DNA replication in bacteria occurs?
(a)During the S phase
(b)Within nucleolus
(c)Prior to fission
(d)Just before transcription

Answer 1

Hint: The bacterial cell also undergoes DNA replication after which the cell started to divide. As we know the nucleolus is not present in prokaryotic bacteria also a well-defined S-phase is absent due to its primitive nature.

Complete answer:
In the process of DNA replication separating the strands of the double helix would provide two templates for the synthesis of new complementary strands, but exactly how new DNA molecules were constructed was still unclear. In the semiconservative replication in one model two strands of the double helix separate during DNA replication and each strand serves as a template from which the new complementary strand is copied, after completion of the replication each double-stranded DNA includes one parental or “old” strand and one “new” strand.
The first step of replication i.e the initiation in bacteria occurs at the origin of replication where supercoiled DNA is unwound by DNA gyrase and made single-stranded by a helicase and then bound by single-stranded binding protein to maintain its single-stranded state. Another enzyme called primase synthesizes a short RNA primer with a free 3′-OH group to which DNA polymerase III can add DNA nucleotides. The leading strand at the time of elongation of DNA is synthesized continuously from a single primer while the lagging strand is synthesized discontinuously in short Okazaki fragments, each requiring its primer. After that, the RNA primers are removed and replaced with DNA nucleotides by bacterial DNA polymerase I, and DNA ligase seals the gaps between these fragments. The last step is the termination of replication where the resolution of circular DNA of the bacteria concatemers by topoisomerase IV to release the two copies of the circular chromosome.
There are some similarities between mitosis and bacterial binary fission that happens in eukaryotes and other humans, perhaps, more importantly, DNA replication happens at the same time as DNA separation during binary fission (unlike in mitosis, where DNA is copied during the S phase, long before its separation in the M phase).

Additional Information: 1) A bacteria i.e E. coli, in their single circular chromosome they have 4.6 million base pairs (Mbp), and all of it is replicated in approximately 42 minutes 1000 nucleotides are added per second.
2) There are three main types of DNA polymerases known in bacteria, those are DNA pol I, DNA pol II, and DNA pol III.
3) The structure of the double helix was first given by James Watson and Francis Crick in 1953 provided a hint as to how DNA is copied during the process of replication.
So, the correct answer is, ‘prior to fission’.

Note: Apart from the main ones above, some other proteins and enzymes are needed to keep DNA replication running smoothly. A ring-shaped protein that keeps the DNA polymerase of the lagging strand from floating off when it restarts at a new Okazaki fragment is called a sliding clamp, it holds DNA polymerase III molecules in place as they start to synthesize DNA.