I read on Wikipedia that when the cell enters prophase during mitosis , the DNA has already been duplicated , that is the DNA is replicated in the chromatin form , but here I see the picture which shows the already condensed DNA ( now chromosome ) divide into sister chromatids. When does DNA divide actually ?
link to wikipedia -https://en.wikipedia.org/wiki/Prophase
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$\begingroup$ Wikipedia is an iffy source to use. Points for adding illustrations though! Can you add link(s) so that anyone who wants to can go and read the articles themselves? If you have any questions or concerns about my thoughts on your answer, please visit the Help Center here biology.stackexchange.com/help $\endgroup$– L.B.Feb 20, 2019 at 18:13
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1$\begingroup$ added the link. $\endgroup$– Aditya PrakashFeb 20, 2019 at 18:32
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$\begingroup$ Thank you! Are you able to reference something that isn't from Wikipedia. This article there looks pretty reputable and such; however, sometimes there is some "shady" stuff there, if you find something else, please feel free to link that here as well. $\endgroup$– L.B.Feb 20, 2019 at 18:38
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1$\begingroup$ I can refer my textbook , but I would be thankful if my question is answered , I have stated my confusion quite clearly and I believe I can get answers too. $\endgroup$– Aditya PrakashFeb 20, 2019 at 18:44
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$\begingroup$ My mistake... I thought you were answering a question not asking one. I totally misread, my apologies, your question is fine. I hope you have a great day! :) $\endgroup$– L.B.Feb 20, 2019 at 18:52
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According to This paper and most biology textbooks, S-phase or synthesis phase is literally defined by the beginning and ending of DNA replication. The first picture does not accurately represent the nature of DNA replication and is instead a model to help people track DNA copies during stages of cell division. DNA is replicated as chromatin and condenses to "double" chromosome form. You can see some micrographs of DNA condensation in this paper. You'll see that they don't condense as single chromatids, but they are already replicated.
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$\begingroup$ That's exactly what should happen , It was constantly bugging me that how could the condensed DNA divide , it should be topologically difficult with all that packaging business , so they should divide in the loose form only , am I right in thinking like this ? $\endgroup$ Feb 20, 2019 at 18:57
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1$\begingroup$ Yes, you're correct. I'm not aware of any circumstances in which condensed DNA can replicate. The first image from the textbook is meant to help student track copies of DNA through the cell cycle, but it does not represent the actual mechanics of chromosome formation. $\endgroup$ Feb 20, 2019 at 19:03