Solution to PS 8 #3

a) Assume that the genome is one large linear  molecule of DNA and that the origin of replicaton is at the midpoint of this chromosome.  Since the replication fork moves in oppositie directions, 60 bp can be replicated per second.  The time required to replicate the entire genome would be:

1.65 x 108 bp / (60 bp/s)= 2.75 x 106 s= 764 hours = 32 days

b)  Assuming that there are 2000 bidirectional origins equally spaced along the DNA molecule  and that initiation occurs simultaneously at all origins, the rate would be 2000 x 2 x 30 bp/s or 1.2 x 105 bp/s and the time to replicate the genome would be:

1.65 x 108 bp/ (1.2 x 105 bp/s)= 1375 s= 23 mins

c)  Assume that the origins are equally spaced and that initiation at all origins is simultaneous.  the required rate of replication is:

1.65 x 108 bp/ (300s)= 5.5 x 105 bp/s

Bidirectional replication at each fork proceeds at an overall rate of 60 bp per second. The minumum number of origins woud be:

5.5 x 105 bp/s/ (60 bp s-1 origin-1)= 9170 origins


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