Reiji and Tuneko Okazaki conducted a now classic experiment in 1968 in which they discovered a population of short fragments synthesized during DNA replication. They introduced a short pulse of 3H -thymidine into a culture of E. coli and extracted DNA from the cells at various intervals. In analyzing the DNA after centrifugation in denaturing gradients, they noticed that as the interval between the time of 3H -thymidine introduction and the time of centrifugation increased, the proportion of short strands decreased and more labeled DNA was found in larger strands. What would account for this observation? a. the ligation of Okazaki fragments by DNA ligase b. the degradation of Okazaki fragments by DNA polymerase I c. the accumulation of Okazaki fragments produced on the lagging strand d. the mutation affecting the activity of DNA ligase Solution Answer C: The accumulation of Okazaki fragments produced on the lagging strand Replication of DNA on lagging strand is discontinuous and replications occur in small sections. These new stretches of DNA are called Okazaki fragments and each one requires its own RNA primer. During DNA replication, each Okazaki fragment is separated by their own RNA primers and are unligated until RNA primers are removed, followed by enzyme ligase connecting (ligating) an Okazaki fragment onto the (now continuous) newly synthesized complementary strand. After the introduction of 3H -thymidine (radioactive thymidine) into a culture of E. coli, 3H –thymidine gradually incorporated into both complimentary strands of leading and lagging strands of DNA during replication. With time, each Okazaki fragment ligated with adjacent fragment with the help of DNA ligase result in the increase of the length of the complementary strand. Due to accumulation and ligation of Okazaki fragments produced on the lagging strand, the proportion of short strands decreased and more labeled DNA was found in larger strands..