A. a closed circular dna in its relaxed form has a linking number (lk) of 500. a supercoiled form of this dna has lk = 495. this supercoiled dna is treated with e. coli topoisomerase i and samples are withdrawn from the reaction at various times and electrophoresed in an agarose gel. sketch how these gels would look. include a lane with the relaxed form, a lane with the supercoiled dna before the enzyme is added, and lanes at various times after the enzyme is added. the final lane should show what the gel looks like when the reaction has reached completion. repeat the experiment using e. coli topoisomerase iv. what do you need in the reaction mix besides the enzyme to make it work? when the topo iv reaction is complete will the product be the same as for topo i? b. discuss the mechanism topo i. why is atp not required to reform a phosphodiester bond after strand passage?