A researcher has synchronized two different E. coli cultures so that all of the

Question

A researcher has synchronized two different E. coli cultures so that all of the cells enter cell division simultaneously. One culture is wild-type E. coli cells, and the other culture is a mutant E. coli that does not have the gene for Dam methylase. He isolates the DNA from both wild-type and mutant E. coli 20 minutes after replication is complete. What is the methylation state for each strain of E. coli? What would be the methylation state for each bacterial strain if you isolated the DNA immediately after replication termination?

Explanation / Answer

Dam methylase is reponsible for adding mythylase group to E.coli. Dam methaylase select adenine base in the sequence 5'-GATC-3' in the newly synthesized DNA strand. Before replication Dam methylse add a methyl group to bith of the strand. However, after replication only one strand contains the mehylated group for a while, at this time it is known as hemi-methylated. Later Dam methylase add methyl group to newly snthesized strand also.

thus, if we look the E.coli strain , both the wild tpye and mutant after 20mins after replicaiton, the wild type E.coli will have the mythylase group in both the strands. However, in the mutant E.coli DNA there will be no mehylase, as it has no Dam methylase gene.

On the other hand if we look at the DNA for boh the E.coli strain immediately after replciaiton, only the of wild type E.coli will contain methylase group at one strand. The mutant E.coli DNa will lack the methylase group.

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