Question

In a bacterial cell, in "the absence of ligase enzyme which of the following events wood occur?

• A. The Okazaki fragmentswill accumulate.
• B. The RNA primer is not synthesized
• C. The replication is not at all initiated
• D. The replication becomes continuous

Answer 1

Answer: (A)

Synthesis of DNA by DNA polymerases occur only in $5^{\prime }\to 3^{\prime }$ direction. One strand called leading strand, is copied in the same direction as the unwinding helix. There is continuous synthesis of DNA in the leading strand in $5^{\prime }\to 3^{\prime }$ and this is called continuous replication. For the other strand, the template strand is oriented in $5^{\prime }\to 3^{\prime }$ direction hence the new strand is to be synthesised in $3^{\prime }\to 5^{\prime }$ direction. Thus, the DNA polymerase complex must move backwards away from the replication fork. Synthesis of new strand occurs discontinuously in a series of short DNA fragments called Okazaki fragments and the strand being synthesised is called lagging strand. The Okazaki fragments are later joined together by DNA ligase thus completing the synthesis of lagging strand.