Question

ΦΧ174 phage provides a model for leading and lagging strand synthesis

There are two types of DNA replication in E. coli:

1- ΦΧ174 phage model: each strand synthesized _____
(unidirectional replication fork)

a) synthesis of the (-) strand to form the double-stranded RF form serves as a model for lagging strand synthesis. We now know that it is a model for re-initiation at lesions.

b) synthesis of the (+) strand to form single-strands for packaging into phage particles servers as a model for leading strand synthesis.

2- OriC origin of bacterial chromosomal replication: both strands synthesized at the same time (bidirectional replication fork)

Answer 1

In E. coli, the ΦX174 phage model represents unidirectional replication where a single strand is synthesized, serving as a model for both leading and lagging strand synthesis. The OriC origin of replication illustrates bidirectional replication with both strands being synthesized at the same time.

Step-by-step explanation:

The ΦX174 phage model and the OriC origin of replication in E. coli illustrate two different methods of DNA replication. In the ΦX174 model, the replication is unidirectional, where the synthesis of the (-) strand forms the double-stranded RF form and acts as a model for lagging strand synthesis. This contrasts with our understanding that it also models re-initiation at lesions. The synthesis of the (+) strand, which forms single strands for packaging into phage particles, serves as a model for leading strand synthesis.

Conversely, the OriC origin represents bidirectional replication. This process begins at the origin of replication, where enzymes open the DNA double helix to form two replication forks. Here, DNA polymerase can only synthesize new strands in the 5' to 3' direction. The leading strand is synthesized continuously, while the lagging strand is created in short segments called Okazaki fragments. Both strands are synthesized simultaneously, thanks to the action of primase and DNA polymerase.