Regarding oncogenesis
Correct Answer: Topoisomerase2 causes break in strands
Description: Topoisomerase2 causes break in strands ; and option C and D is also answer ref Harrison 16/e p453; 454; Robbins 7/e Cell Cycle Inhibitor Proteins Topoisomerases can fix these topological problems and are separated into two types depending on the number of strands cut in one round of action: Both these classes of enzyme utilize a conserved tyrosine. However these enzymes are structurally and mechanistically different. For a video of this process click here. A type I topoisomerase cuts one strand of a DNA double helix, relaxation occurs, and then the cut strand is re-ligated. Cutting one strand allows the pa of the molecule on one side of the cut to rotate around the uncut strand, thereby reducing stress from too much or too little twist in the helix. Such stress is introduced when the DNA strand is "supercoiled" or uncoiled to or from higher orders of coiling. A type II topoisomerase cuts both strands of one DNA double helix, passes another unbroken DNA helix through it, and then re-ligates the cut strands. Type II topoisomerases utilize ATP hydrolysis and are subdivided into two subclasses which possess similar structure and mechanisms: Type IIA topoisomerases which include eukaryotic and eukaryal viral Topoisomerase IIa and Topoisomerase IIb, bacterial gyrase, and topoisomerase IV. Type IIB topoisomerases, which include Topoisomerase VI found in archaea
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