The diploid genome of Drosophila melanogaster is approximate

The diploid genome of Drosophila melanogaster is approximately 3.2x10^8 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

Since the synthesis of DNA is occurring bidirectionally, we can perform the calculations with double the given speed i.e. total amount of DNA synthesized per second = 30×2 = 60 bp

a. Time taken to replicate entire genome from a single bidirectional origin = 3.2×10⁸/60 = 5333333 seconds (= 1481.5 hours!!!)

b. Time taken to replicate entire genome from 2000 bidirectional origins = (3.2×10⁸)/(60×2000) = 2667 seconds (= 44.45 minutes only)