2. The diagram shows a length of template DNA and three Okazaki fragments of the

Question

2. The diagram shows a length of template DNA and three Okazaki fragments of the lagging strand. The RNA primers have not yet been removed. (50 points total) lagging strand template DNA 5 3 3 5 primer RNA primer RNA primer RNA left Okazaki fragment middle Okazaki fragment right Okazaki fragment a. (10 points) Which Okazaki fragment was synthesized first, the one on the left, in the middle, or to the right? b. (20 points) Before the primer of the left Okazaki fragment can be removed by DNA polymerase I and the gap can be filled in, is it necessary for the middle Okazaki fragment to have already been synthesized? Explain why or why not. c. (20 points) After DNA polymerase I removes the primer of the middle Okazaki fragment and fills in the gap with DNA, where will DNA ligase act to unite the DNA backbone, at the white arrow, the black arrow, or both locations? Briefly explain.

Explanation / Answer

1.The right Okazaki fragment synthesized first among all okazaki fragments as 5' to 3' direction is lagging strand synthesis direction.

2.yes it's necessary to middle okazaki fragments to have already been synthesized because then it's possible for DNA polymerase to remove rna primer and fill the gap of left okazaki fragments.

3.Dna ligase act to unite the dna backbone at the White arrow where it synthesise phosphodiester bond again 5' to 3' direction.

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