DNA replication and replication forks problem

[growingpains]

This is from BR Bio Section IX (Genetic Information), Passage VII, Question 39:

A given culture of mammalian DNA has 1.2 meters of duplex DNA in each cell and the DNA synthesis phase for these cells is 5 hours. How many replication forks are there, if the growth rate in these cells is 16 um/minute?

Here's how I solved it:

1.2 meters / 5 hours = 0.24 meters/hour = 240,000 um/hour = 4000 um/min
4000 um/min / 16 um/min = 250 forks

But now, shouldn't the answer actually be roughly 125 forks, because each fork provides roughly 2x the rate of replication?




Also, in a similar light, if a strand of DNA has 4000 kilobase pairs and each Okazaki fragment is 1 kilobase long, wouldn't there be 8000 Okazaki fragments? 4000 kb / 1 kb x 2 (because there are two strands

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[bajoneswadup]

how exactly would each fork provide 2x the rate? and i'm pretty certain there would
be 4,000 okazaki fragments. if each strand has 4000kb, so 8000kb total, the okazaki fragments are only produced on the lagging strand- so its 4000

 

[milski]

The consensus on this one was leaning towards a TBR error but we never got a confirmation.

http://forums.studentdoctor.net/showthread.php?t=886875

 

[growingpains]

how exactly would each fork provide 2x the rate? and i'm pretty certain there would
be 4,000 okazaki fragments. if each strand has 4000kb, so 8000kb total, the okazaki fragments are only produced on the lagging strand- so its 4000

My mistake, I misused the term "fork." By fork, I meant replication bubble, in which there are two forks each.