E. coli has one circular DNA for its genome. Its size is about 4.5 to 4.7 Mb. The time to synthesize one strand therefore can be approximated by distance divided by speed, which is about 60 to 90 minutes.

Interestingly, the time takes an E. coli to divide can be as short as 20 minutes. It may seem too short, however, it turns out that when the condition is right, E. coli will carry out a nested replication. A new round of replication will start even before the current one finished. This allows E. coli to grow exponentially when there are enough nutrients.

According to this source, the E. Coli genome consists of 4,600,000 base pairs. Using 1000 base pairs per second, it would take 4,600 seconds- or about 1 hour and 17 minutes.

For this, you need to know the size of the E. coli genome, which is about 4.6 million base pairs. Now it's just an algebra problem: divide the number of base pairs by the rate of polymerization.

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