question_answer 85)

  Replication was allowed to take place in the presence of radioactive eoxynucleotides precursors in E.coli that was a mutant for DNA ligase. Newly synthesized radioactive DNA was purified and strands were separated by denaturation. These were centrifuged using density gradient centrifugation. Which of the following would be a correct result?   (a) (b)     (c)   (d)  

Answer:

                    In above case, as E.coli is a mutant for DNA ligase, it will result in no further joining ofOkazaki fragments on lagging strand. This will ultimately result into the formation of both high molecular weight fragments(on leading strands) and low molecular weight fragments (on lagging strand). Hence, onlythe graph (a) could be the appropriate result after centrifugation.