Question

In case of prokaryotic cell, the ori site can be defined as:

(1) A-T rich region

(2) G-C rich region

(3) A-T & G-C rich may be

(4) None of the above

(Note: Explain reason for all options for which they are considered/not considered)

Answer 1

In case of prokaryotic cell, the ori site can be defined as A-T rich region as the AT‐rich region is exactly the site where a replication complex is formed.

oriC—contains multiple binding sites for the initiator protein DnaA. It consists of three A–T rich 13-mer repeats and four 9-mer repeats. Ten to 20 monomers of the replication initiator protein DnaA bind to the 9-mer repeats, and the DNA coils around this protein complex forming a protein core. This coiling stimulates the AT rich region in the 13-mer sequence to unwind, allowing the helicase loader DnaC to load the replicative helicase DnaB to each of the two unwound DNA strands.