Bidirectional Replication

Bidirectional replication is a method of DNA replication used by many organisms e.g. Paramecium. Bidirectional replication consists of the linear chromosome replicating in two directions, starting from one point, the replication origin. The chromosome also has two replication forks which are the regions where nucleotides are actively added to growing strands. The linear chromosomes have several origins of replication and two replication forks for each of these, replication therefore occurs much more quickly. At all replication origins, replication takes place in a bidirectional format which results in the formation of ‘replication bubbles’. These bubbles grow in size as replication continues. Eventually, two replication forks (at each end of a bubble) meet, at which point they fuse together producing a larger bubble. Ultimately, all the replication bubbles along the chromosome merge into one large bubble joint only at the telomeres; these split to give two identical strands of DNA. This process continues to produce a many strands of DNA which are then passed on todaughter cells (adapted from [1]).