Question from USMLE sample 2010 test

[drmedstudent]

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i was wondering if any1 could explain why question 64 is (A).

here's the link
http://www.usmle.org/Examinations/step1/2010Step1.pdf

here's how i did it, since its 5'CGG3' to 5'TGG3' mutation, you get 5'CCG3' to 5'CCA3' mRNA mutation...which according to Genetic Code is Proline to Proline...lol. so im prolly doing it wrong. help any1?

im pretty sure this might be obvious but im not getting cuz im an idiot

 

[Sol Rosenberg]

It says the mutation is in the coding strand ("...in the gene encoding....,") not the template strand. So, yes, this one was as easy as just look it up in the table (I wondered if they were trying to trick me when I saw this one too...)

 

[drmedstudent]

ok i get it...so whenever they say something about a "gene encoding something".....it actually means that its complement strand will transcribe the mRNA and translate protein rite?

 

[Ableton]

The coding strand has the gene sequence. The template strand is the complementary DNA sequence to the coding sequence, and that is what is transcribed into mRNA. So the resulting mRNA has the same sequence as the coding strand, but U instead of T...

Look at it this way:

3'...CAGTGC...5' - template
5'...GTCACG...3' - gene (coding strand)

mRNA would then be 5'...GUCACG...3'

I hope this makes sense?

 

[drmedstudent]

yep makes sense...thanks a bunch to both of you

can i bother u guys with another question from that same sample test?
question 78.

thanks again

 

[MilkmanAl]

Well, D is your ladder, so that's a garbage answer. It's basically asking you if the virus should be the same (A), different in all (B), or "depends" (C). I'd choose A since it tells you it's one virus. Unless HSV1 has some weird mutation trick I'm forgetting, the scrapings should all contain more or less the same virus.

 

[Sol Rosenberg]

Yeah, HSV-1 hides out in the trigeminal ganglia, so when it reactivates all of the vesicles are essentially coming from the same population of virus. Maybe that's even too detailed an explanation for the question, but that's what I used to convince myself that there wasn't likely some mutation that would cause the different vesicles to be slightly different.

 

[drmedstudent]

would any1 care to explain question 109 from the sample test? thanks!!

 

[kryptik]

i think kaplan puts out an explanation to the questions, you can download on their site for free

 

[drmedstudent]

oh really, do u know where i can get it? i tried finding it but couldnt get it

 

[Xtrasystolic]

They haven't put up the explanations for items from 2010 yet.

Those for 2009 are available on kaptest, you probably have to sign in though.

 

[drmedstudent]

They haven't put up the explanations for items from 2010 yet.

Those for 2009 are available on kaptest, you probably have to sign in though.

so u have to be a enrolled in kaplan to access it?

 

[kryptik]

so u have to be a enrolled in kaplan to access it?

no u dont its free to download, maybe you may have to create a login though not sure, but its definitely free to download

 

[aashkab]

is this the free nbme 150?

 

[aashkab]

The coding strand has the gene sequence. The template strand is the complementary DNA sequence to the coding sequence, and that is what is transcribed into mRNA. So the resulting mRNA has the same sequence as the coding strand, but U instead of T...

Look at it this way:

3'...CAGTGC...5' - template
5'...GTCACG...3' - gene (coding strand)

mRNA would then be 5'...GUCACG...3'

I hope this makes sense?

so the 5 prime to 3 prime strand is always the gene (coding) strand while the 3 prime to 5 prime is always the rna template.

the 5' to 3' rna polymerase then acts on the 3' to 5' prime template dna strand?