DNA Structure and Replication

ID #1722

Do prokaryotes have chromatin? and can you explain more thoroughly the difference between chromatin and chromosomes? and one last thing, what do you mean when you say topoisomerase "nicks," winds or unwinds and reseals DNA?


Depends on how strict your definition is. I've read numerous explanations for what actually constitutes chromatin, and the one I use for simplicity in this course is "DNA complexed with protein." By that definition, then bacteria definitely have chromatin because they have histone-like proteins associated with their DNA. Other definitions would lead to different answers, but let's not go there right now.

A chromosome is a unique piece of chromatin. Humans have lots of chromatin in their cells' nuclei, but that chromatin is not found in one gigantic fragment. Instead, it's found spread out over 23 different molecules called chromosomes, and we have a pair of each of those, giving us a total of 46 chromosomes.

A topoisomerase cuts the phosphodiester backbone, either twists or unwinds the strand(s), and then seals the cut right back up. At no point are bases removed or added, it just serves to relax or induce supercoils.

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