3. In rich growth media, E. coli can increase its growth rate so that it divides

Question

3. In rich growth media, E. coli can increase its growth rate so that it divides every 20 minutes. However the time for a growth fork to complete replicating the chromosome remains about the same as in poorer medium. How can you explain the discrepancy?

4. The thymine analog 5 bromouracil is incorporated into DNA in place of thymine. It increases the density of DNA by more than 15N, allowing better resolution of centrifuge bands. However 5BU increases the enol tautomerization of the base. Would you predict that 5BU is a mutagen? Why or why not?  

Explanation / Answer

3. Growth rate is known to be the rate at which the population of a culture inceases.

In a rich growth media, nutrients are in abundance. This facilitates favourable conditions for E. coli cell growth and division. Which implies that a higher percentage of E. coli would grow and go for cell division in a nutrient rich media. So we will get more number of cells that are bigger.

There would be no change in the growth fork as chromosomal replication will occur only when the cell has all the components to facilitate the replication.

The growth rate will determine how fast a cell can get ready for replication. However the time taken for the chromosomal replication will be independant of the growth rate.

Therefore, a growth fork for completing the replication of the chromosome will remain the same.

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