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Some E. coli mutants contain defective DNA ligase. When the DNA produced by these mutants are...

Some E. coli mutants contain defective DNA ligase. When the DNA produced by these mutants are analyzed, two products are isolated. One corresponds to a high molecular weight fraction, the other to a low molecular weight fraction. Explain this observation.

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Answer #1

DNA ligase serves to join the Okazaki fragment during DNA replication, which leads to the formation of the lagging strand.

The formation of the leading strand does not require DNA ligase activity because it occurs in a continuous manner.

Therefore when E. coli mutants containing defective DNA ligase were analyzed two products were isolated. The high molecular weight fraction corresponds to the leading strand because it has been synthesized in a continuous manner. The low molecular weight fraction corresponds to the lagging strand, which has not been ligated due to defective DNA ligase. The separate Okazaki fragments give rise to low molecular weight fraction.

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