Amplifying CAG Repeats? - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 06-12-2013
USMLE Forums Scout
 
Steps History: ---
Posts: 57
Threads: 30
Thanked 15 Times in 11 Posts
Reputation: 25
DNA Amplifying CAG Repeats?

James K. is a Huntington disease patient who has recently been
institutionalized and requires constant nursing care. His wife is unaffected, 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
containing the CAG repeat, shown below. Which of the following sets of primers
would be used to amplify the CAG repeat in the brackets ([CAG]n)?

...CTC AAG TCC TTC [CAG]n CAA CAG CCG CCA...
(A) GAGTTCAGGAAG and TGGCGGCTGTTG
(B) GAACTCCCTGAG and CCGCCACCGCCG
(C) GAACTCCCTGAG and TGGCGGCTGTTG
(D) CTCAAGTCCTTC and TGGCGGCTGTTC
(E) CTCAAGTCCTTC and TGGCGGCTGTTG

i cant get the q, so no doubt, i dont know ans either
please help friends ...
Reply With Quote Quick reply to this message
The above post was thanked by:
abeer (06-12-2013), Usmle16Forall (11-22-2016)



  #2  
Old 06-12-2013
abeer's Avatar
USMLE Forums Guru
 
Steps History: 1+CK+CS+3
Posts: 369
Threads: 3
Thanked 195 Times in 83 Posts
Reputation: 205
Default

yaa even i need help on this one..
Reply With Quote Quick reply to this message
  #3  
Old 06-12-2013
USMLE Forums Scout
 
Steps History: Not yet
Posts: 13
Threads: 6
Thanked 5 Times in 3 Posts
Reputation: 15
Default

This is the dna strand:

5' ...CTC AAG TCC TTC [CAG]n CAA CAG CCG CCA... 3'
3' ...GAG TTC AGG AAG[GTC]n GTT GTC GGC GGT... 5'

for pcr the primer must made from 3' to 5' end of dna surrounding the [CAG] codon.
therefore,
for top sequence:
DNA sequence - 5' CAA CAG CCG CCA 3'
RNA primer - 3' GTT GTC GGC GGT 5'
sequence is always written from 5' to 3' so, 5' TGG CGG CTG TTG 3'

for bottom sequence:
DNA sequence - 3' GAG TTC AGG AAG 5'
RNA Primer - 5' CTC AAG TCC TTC 3'

Answer is option E
Reply With Quote Quick reply to this message
The above post was thanked by:
Novobiocin (06-17-2013), Usmle16Forall (11-22-2016)
 
  #4  
Old 06-12-2013
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,109
Threads: 31
Thanked 521 Times in 394 Posts
Reputation: 540
Default

Quote:
Originally Posted by shoty View Post
James K. is a Huntington disease patient who has recently been
institutionalized and requires constant nursing care. His wife is unaffected, 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
containing the CAG repeat, shown below. Which of the following sets of primers
would be used to amplify the CAG repeat in the brackets ([CAG]n)?

...CTC AAG TCC TTC [CAG]n CAA CAG CCG CCA...
(A) GAGTTCAGGAAG and TGGCGGCTGTTG
(B) GAACTCCCTGAG and CCGCCACCGCCG
(C) GAACTCCCTGAG and TGGCGGCTGTTG
(D) CTCAAGTCCTTC and TGGCGGCTGTTC
(E) CTCAAGTCCTTC and TGGCGGCTGTTG

i cant get the q, so no doubt, i dont know ans either
please help friends ...


Looks difficult.
I would go for
E.
__________________
In USMLE, “Any fool can know. The point is to understand.”
Reply With Quote Quick reply to this message
  #5  
Old 06-12-2013
USMLE Forums Scout
 
Steps History: ---
Posts: 57
Threads: 30
Thanked 15 Times in 11 Posts
Reputation: 25
Default

Quote:
Originally Posted by SkyRad View Post
This is the dna strand:

5' ...CTC AAG TCC TTC [CAG]n CAA CAG CCG CCA... 3'
3' ...GAG TTC AGG AAG[GTC]n GTT GTC GGC GGT... 5'

for pcr the primer must made from 3' to 5' end of dna surrounding the [CAG] codon.
therefore,
for top sequence:
DNA sequence - 5' CAA CAG CCG CCA 3'
RNA primer - 3' GTT GTC GGC GGT 5'
sequence is always written from 5' to 3' so, 5' TGG CGG CTG TTG 3'

for bottom sequence:
DNA sequence - 3' GAG TTC AGG AAG 5'
RNA Primer - 5' CTC AAG TCC TTC 3'

Answer is option E
thanks for nice explanation good luck
Reply With Quote Quick reply to this message
  #6  
Old 06-12-2013
medicalbiology's Avatar
USMLE Forums Guru
 
Steps History: Not yet
Posts: 394
Threads: 128
Thanked 109 Times in 89 Posts
Reputation: 119
Default

Little confusion....for top sequence u take dna sequence as 5'CAA..... BUT for bottom sequnce why u take dna sequence 5'GAG... i mean u should take 5'CTC...CONFUSED
Reply With Quote Quick reply to this message
  #7  
Old 06-12-2013
USMLE Forums Scout
 
Steps History: Not yet
Posts: 13
Threads: 6
Thanked 5 Times in 3 Posts
Reputation: 15
Default

Quote:
Originally Posted by medicalbiology View Post
Little confusion....for top sequence u take dna sequence as 5'CAA..... BUT for bottom sequnce why u take dna sequence 5'GAG... i mean u should take 5'CTC...CONFUSED
First of all its 3' GAG...

5' CTC is the top sequence of DNA, have already worked out the primer for that.
for lower strand, DNA Polymerase will read from 3' to 5' and make dna from 5' to 3' so the primer must be made complementary to the 3' to 5' dna sequence.

<- DNA polymerase
3' GTT GTC GGC GGT... 5' PRIMER 1
5' ...CTC AAG TCC TTC [CAG]n CAA CAG CCG CCA... 3'
3' ...GAG TTC AGG AAG[GTC]n GTT GTC GGC GGT... 5'
5' ...CTC AAG TCC TTC 3' PRIMER 2
DNA polymerase ->
Reply With Quote Quick reply to this message
The above post was thanked by:
Novobiocin (06-17-2013), Usmle16Forall (11-22-2016)
  #8  
Old 06-13-2013
medicalbiology's Avatar
USMLE Forums Guru
 
Steps History: Not yet
Posts: 394
Threads: 128
Thanked 109 Times in 89 Posts
Reputation: 119
Default

Thankx skyrad we really need people like u.
Reply With Quote Quick reply to this message



Reply

Tags
Molecular-Biology-, Step-1-Questions

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Trinucleotide Repeats Diseases ashishkabir USMLE Step 1 Bits & Pieces 4 12-01-2016 11:20 PM
Triplet Repeats Mnemonics rasheed USMLE Step 1 Mnemonics 8 04-30-2012 07:01 PM
number of CAG repeats nativedoc2 USMLE Step 1 Forum 0 10-03-2011 04:50 PM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)