2009 Exam 2

This will be graded very strictly and will not be re

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Unformatted text preview: e, Biology 231's first-ever extra credit exam question! This will be graded very strictly and will not be re-graded. W e learned about telom erase, a n extraordinary complex of p rotein and R N A that c an solve the “end problem” of e ucaryotic D N A replication. (a) 2 pts. In two sentences, describe concisely the “end problem.” (Not the solution, just the problem) A fte r c o n v en tio n al D N A re p licatio n , w h en th e last R N A p rim er is rem oved from the 5' e nd of the new ly synthesized D N A s trand, it leaves a gap that c an’t b e filled by norm al replication, w hich requires a n existing free 3' -O H . W ithout a c om plim entary strand, this singlestra n d ed stre tch o f p are n tal D N A w ill b e d eg ra d ed , th u s sh o rte n in g b o th stra n d s – an d th e ch ro m o so m e – w ith each ro u n d o f rep licatio n . ( b) 2 pts. If y ou w ere designing the cell, y ou m ight b e able to come up w ith a different w ay to s olve the end problem, u s ing D N A p olym erases o nly. In one sentence, describe a w ay to do this: H ow a bout a special, 5 '-end-specific D N A p olym erase (“endase”) that could synthesize n ew D N A in the 3 '-to-5' d irection, extending the daughter strand to the sam e length as the p arental strand. A ls o s ugge s te d: p rim e r-fre e D N A s ynthe sis , o r p rim ing w ith D N A (+2) m a ny c irc ula r c hrom os om e s (+2) a c tio n o f F ly in g S p a g h e tti M o n s te r ( n o c re d it) a lc h e m y (n o c re d it) d u c t ta p e (n o c re d it) -14-...
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