BIOL308 Lecture Notes - Lecture 5: Histone Deacetylase, Garland Science, Amine
4 Feb 2015
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Dna has to be packaged into nucleus (or cell in case of prokaryotes), but it also has to be accessible to transcriptional and replicational machineries. Positive supercoiling dna overwound: reduced chance for dna- protein interaction. Negative supercoiling - dna underwound: negative supercoils store energy, which can be converted into untwisting (unwinding) of double helix that could help strand separation - untwisting favored (important for replication and transcription) L (linking number) = t (twisting) + w (writhing); L can only be changed by breaking one or both strands of the dna, winding. And them tighter or looser, and rejoining the ends. Enzymes essential in both prokaryotes and eukaryotes; recognize and regulate supercoiling and make cuts in dna - play an important role in replication and transcription. Prokaryotic: topoisomerase i: nicking-closing enzyme, makes transient cuts in one strand. Changes l # in steps of 1: topoisomerase ii relaxes positive supercoiled dnas uses the energy of.
