The diploid genome of Drosophila melanogaster is approximate

The diploid genome of Drosophila melanogaster is approximately 3.2x10⁸ base pairs of DNA. DNA synthesis occurs at approximately 30 bp/second. Calculate the minimum time required to replicate the entire genome if replication were initiated:

A.) at a single bidirectional origin

B.) at 2000 bidirectional origins

Solution

A. Genome is a large linear molecule of DNA and the origin of replication starts at the midpoint of the chromosome. As the replication forks moves in two directions, so the DNA synthesis occurs at 60bp/s. The time required to replicate the entire genome would be

3.2 x 10⁸ / 60bp/s = 5.3 x 10⁶ s = 61.3 days

B. If there are 2000 bidirectional origins equally spaced along the DNA molecule. The initiation occurs at all origins, the rate would be 2000 x 2 x 30 bp/s or 1.2 x 10⁵ bp/s

3.2 x 10⁸ / 1.2 x 10⁵ = 2666 s = 44.4 mins