During DNA replication, the synthesized okazaki fragments adjacent to each other are joined up directly by DNA ligase-catalyzed phosphodiester bond formation. Can someone point out to me which part of this statement says it's false? All I know is that the fragments are joined together by DNA ligase, which can only mean the part about the phosphodiester bond is wrong, but arent the 2 nucleotides joined by a phosphodiester aka nucleotide bond?
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1$\begingroup$ This seems to be a garbled version of a trick MCQ which is of no interest to anyone. Rather than vote for the half answer, vote to close it. $\endgroup$– DavidCommented Feb 9, 2018 at 16:49
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4 Answers
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I'm pretty sure the "phosphodiester bond" part is correct.
The only thing I can think of that might be questionable is the word "directly". If directly = immediately, then the sentence could be termed false, because they aren't joined immediately.
Even then, it seems like that's just grasping at straws, so I wouldn't worry too much about it. It sounds like you understand the concept, which is what matters.
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The best guess I could make is "directly". Okazaki fragments also contain RNA primers, which need to be replaced by DNA fragments. This is why joining Okazaki fragments together is a bit longer process. In short, the RNA primers are first removed by Flap endonuclease I and replaced by DNA Polymerase $\ce{\delta}$, after which these fragments are joined by DNA ligase I. I would suggest you read the Wikipedia article about Okazaki fragments.
answered Nov 11, 2017 at 11:09
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$\begingroup$ You're most welcome :) If my post really answers your question, please consider selecting it as correct. It gives points to both the answerer (me) and the asker (you) ;) $\endgroup$ Commented Nov 12, 2017 at 11:31
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Okazaki fragment maturation involves a gap-filling (between adjacent Okazaki fragments) and strand-displacement (5'-end of the downstream Okazaki fragment) DNA synthesis by DNA polymerase δ (Polδ) which produces a ligatable nick; the nicked DNA is the substrate for DNA ligase.
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Okazaki fragments do not attach to the lagging strand adjacent to one-another, but rather, attach randomly, some distance from one-another.
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1$\begingroup$ My answer is correct. Okazaki fragments do NOT line up adjacent to one another. They are some distance apart, and the distance between them must be filled in. That was the error in the question. $\endgroup$ Commented Dec 11, 2017 at 21:09