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

a. If the single bidirectional origen: 2 replication forks act at a time and gives 60bp/sec. Then total time required is 3.2 x 10^8 / 60 = 53 x 10^5 Sec = 1472 hr

b. If 2000 bidirectional origins are there, then 4000 replication forks exist. Each fork 30 bp/sec. Then 4000 forks synthesizes 4000 x 30 = 120000 bp/Sec. Then time required for complete replication is: 3.2 x 10^8 / 120000

= 2667 Sec or 45 min