BIOCHEM 3G03 Chapter Notes - Chapter 20: Dna Supercoil, Origin Recognition Complex, Dna Polymerase
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30 Nov 2016
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Dna duplicated through separation of strands followed by assembly of two new complementary strands. Dna molecule twists up on itself supercoiling. Each writhe, or supercoil in dna is the result of over twisting or under twisting the dna helix. Topoisomerase cuts one of both strands of the supercoiled dna, altering the structure and then reconnecting the broken strands. Type i: cut on dna strand: o(cid:272)(cid:272)u(cid:396)s i(cid:374) all (cid:272)ells a(cid:374)d alte(cid:396)s dna(cid:859)s heli(cid:272)al twisting. Ia nick the dna cut the backbone of one strand, pass the intact strand through the break and then seal the broken strand in order to unwind the dna by one turn. Ib also cuts one strand but holds the dna on one side of the nick while allowing the. Human topoisomerase i: type ib with 4 domains that encircle the dna. Surface that contacts dna is rich in + groups, that can interact with the backbone phosphate groups of about 10 bp.
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