am-nicole
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James k. is a Huntington diease patient who has recently been institutionalzed and requiers constant nursing care.his wife is unaffecte ,and they have a 38-year -old daughter. Delia,who has 4 children ranging in age from 8 to 15 years.Delia wishes to know whether she has inherited the disease-producing allele from her father.PCR amplification is carried out on the region cotaining the CAG repeat, shown below.which of the following sets of primers would be used to used to amplify the CAG repeat in the brackets ([CAG]n)?
GAG TCC CTC AAG TCC TTC [CAG]n CAA CAG CCG CCA CCG CCG
(A)- CTCAGGGAGTTCAGGAAG and CGGCGGTGGCGGCTGTTG
(B)- CTTCCTGAACTCCCTGAG and CAACAGCCGCCACCGCCG
(C)- CTTCCTGAACTCCCTGAG and CGGCGGTGGCGGCTGTTG
(D)- GAGTCCCTCAAGTCCTTC and CGGCGGTGGCGGCTGTTG
(E)- GAGTCCCTCAAGTCCTTC and GTTGTCGGCGGTGGCGGC
the answer is D WHY???????????
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| pringo
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Q. : GAG TCC CTC AAG TCC TTC [CAG]n CAA CAG CCG CCA CCG CCG
(A)- CTCAGGGAGTTCAGGAAG and CGGCGGTGGCGGCTGTTG
(B)- CTTCCTGAACTCCCTGAG and CAACAGCCGCCACCGCCG
(C)- CTTCCTGAACTCCCTGAG and CGGCGGTGGCGGCTGTTG
(D)- GAGTCCCTCAAGTCCTTC and CGGCGGTGGCGGCTGTTG
(E)- GAGTCCCTCAAGTCCTTC and GTTGTCGGCGGTGGCGGC
Here, we only have one strand, so we should first make the complementary strand & then ( heating + cooling ) ----> ( haeting + cooling ).........; as a result we need a primer (p.) for the strand in the Q. & a p. for the comp. one, which it is not in the Q.
Replication is always from 5' to 3'. If we pretend that the mentioned strand is in this way :
3' GAG TCC.......[CAG]........CCG CCG 5' so comp. strand is :
5' CTC AGG.......................GGC GGC 3'.
Then after heating & separation of these two strands the P. for the second strand should be : ..............CCG CCG 5' , which there is no option in the Q.
( to make us dizzy !!!!! the direction of the written P. in the Q. is L. to R., instead of R. to L.)
So the main strand is as : 5' GAG TCC.........[CAG]............CCG CCG 3' ===> comp.is :
3' CTC AGG.............................GGC GGC 5'
then heating & separation ===> 3' CTC AGG.........................CCG CCG 5'
5' GAG TCC.........................GGC GGC 3'
so the Ps. are GAG TCC...... & .........GGC GGC ;which one is written from L. to R.
I hope I could have helped u. ( though I tried so hard to type the strands under eachother, but no success !!!!
Bye to all.
Edited by pringo on 02/15/07 - 04:53 PM
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| am-nicole
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I don't think so. please anybody who knows the answer, can you kindly explain it??????
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| keepgoing
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first take rough sheet of a paper now
1.rt wats in quest stem i.e
5'GAG......................CCG CCG3'
2.now in step 2 write its complimentr strand i.e
3' CTC.....................GGC GGC5'
ok on heating we will get these two seperated now adding oligonucleitide primers for each strand
from step 1 starting from 3' end add its compl oligonucleiotide that wud be----- >>CGGCGG....
from step 2 step our 2nd strand to 3'end add GAG...........
hope u got nw
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| indidoc1
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ok.. i hv got some time at my hand.. so will ty to explain in simpler terms what KG ws saying...
Basically, u know that all new strands r gonna be synthesized 5'-----3'
n all strands r written 5'----3' Right??
So.. now lets see...
This is what we r given..
5' GAG TCC CTC AAG TCC TTC [CAG]n CAA CAG CCG CCA CCG CCG 3'
ok.. so if u wanna synthesize it.. u need a primer to attach at the 3' end.. right?
n when we write that one down, we ll again write it frm 5'----3'
So, the primer fr the given strand is 5' CGG CGG TGG CGG CTG TTG 3'
...CONTD
Edited by indidoc1 on 03/08/07 - 10:15 AM
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| indidoc1
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Thats cool but if u really wanna rev up the process, y don't we make use of the other strand of the given chromosome as well?? coz every DNA hs 2 strands
So, given 5' GAG TCC CTC AAG TCC TTC [CAG]n CAA CAG CCG CCA CCG CCG 3'
The complimentary strand is gonna be again written 5'--3'..
5' CGG CGG TGG CGG CTG TTG [CTG]n GAA GGA CTT GAG GGA CTC 3'
Remember.. this is the strand that we wanna amplify in addition to the given one.. So we get double the number of DNA in 1/2 time
Fr this, we need a primer complimentary to its 3' end.. which is  again written 5'---3'
5' GAG TCC CTC AAG TCC TTC 3'
Combine the above 2 answers n its DDDDDD eureka!!
Edited by indidoc1 on 03/08/07 - 10:16 AM
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| indidoc1
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all that i hv written above is just a way to explain in minute detail.. There is a way wth which u cn reason out to the ans as well.. Didn't post it earlier coz didn't want to confuse u..
It goes like this..
We get the 1st primer (to the given strand) as i wrote in the 1st part..
Fr the second primer.. Pay attention ..there's gonna be some word war here  ..
We need a primer fr the strand complimentary to the given strand...
now .. we know that a primer is complimentary to the 3' end of the parent strand..
So, in other words, we need a primer,... which is complimentary to the 3' end of the complimentary strand..
If u work on this.. u ll see its gonna be the 5' end of the parent strand itself..
So that way... u get the answer faster..
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| indidoc1
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hope that helps u.. 
PHEW!!! 
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| keepgoing
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goodwork indi:clap:
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| indidoc1
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Thanks fr the clap KG, :bow:
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| epica
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Is this Q from Q book or Kaplan Bioc book 2007?
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| am-nicole
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thank you all
Edited by am-nicole on 04/22/07 - 09:07 PM
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