[indian]

A genetic disease in which there's a complete loss of enzyme activity. A northern blot was done on tissue sample and revealed normal enzyme amount. What could explain the genetic defect?
-Gene mutation
-Splicing mutation
-Promotor mutation
-Transcriptional defect
-Nonsense mutation
-Silent mutation
-Missense mutation
-Postranslational defect

 

[khanar]

Because the northern blot is normal (which means mRNA is normal) then I'd choose post-translation defect as the correct answer.

 

[sak2114]

I also think the answer is post-translational..

 

[indian]

post-translational is not the correct answer
because such defects usually do not cause complete enzyme deficiency
Try another one

 

[ahassan]

I agree post-translational defect.

 

[ahassan]

okay my bad

was thinking more like splice mutation

going wid my gut here

 

[indian]

okay my bad

was thinking more like splice mutation

going wid my gut here

splice site mutation would result in an abnormal mature mRNA which is against the normal Northern blot!
Try another

 

[ahassan]

yeah rite

then i think silent mutation

 

[indian]

yeah rite

then i think silent mutation

silent mutation does not cause any clinical disease at all as the name implies.
Try another

 

[ahassan]

normal enzyme amount but is not functional.....

mis sense mutation

 

[indian]

normal enzyme amount but is not functional.....

mis sense mutation

Finally you got it rite The correct answer is missense mutation

 

[ahassan]

thank God !!

good confusing answers.

Good learning tool.

 

[khanar]

It's not even missense mutation because mis sense mutation just causes an amino acid replacement and the enzyme may be still functional.
The correct answer is nonsense mutation which causes a non functional enzyme.

 

[ahassan]

but won't nonsense mutation give a truncated protein via a stop codon formation? northern blot will be negative me thinks

 

[khanar]

but won't nonsense mutation give a truncated protein via a stop codon formation? northern blot will be negative me thinks

mRNA will be completely transcribed as usual and develop into mature mRNA the stop codon will be encountered during the translation process and the protein will be truncated and non functional.

 

[indian]

Sorry I was wrong
Firas is right
It should be nonsense mutation

 

[DrSeddik]

I don't get it, isn't Northern blot test supposed to detect RNA sequence too. Or just the length.

 

[khanar]

I don't get it, isn't Northern blot test supposed to detect RNA sequence too. Or just the length.

Blotting will not occur if the probe is not complementary to the mRNA sequence. So yes it detects correct sequence mRNA strands!!
I think the question is designed wrong. They should say normal amount of mRNA and they should not say normal Northern blot.
I think I've seen a similar question in Kaplan Qbank that had a similar theme and concept and I think they mentioned just mRNA they did not say Northern blot.

 

[DrSeddik]

feeooow . That's a relief, I thought I got it all wrong.