[Patrycja]

I have got a question relating the DNA replication forks and I have been unable to find out the answer from my books. I am new to molecular biology only started it about two weeks ago.

I know and understand the idea of the DNA replication happening in the replication forks. So if we presume that the replication fork goes into left side with the top strand being the leading str and the bottom the lagging it makes all sense to me. But its says in the book that the replication forks are bidirectional so it can go to right hand side at the same time. So does that mean that if it goes to right side the top strand become the lagging strand while the bottom becomes the leading strand??

Thank you

[CharonY]

It is easier to think in terms of 5' to 3' direction rather than using right-left, which are pretty much meaningless. That being said, depending on the position relative to the origin of replication, the lagging strand becomes the leading strand and vice versa. It is easy to understand if you remember that replication is always 5' to 3'. The strand that leads away from the origin with 5'-3' direction is always the leading one. However, on the other side of the origin it will move from 3' to 5' and hence become the lagging strand:

3'<-<-<-Ori->->->5'