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Old 06-10-2012
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DNA mRNA Sequence change upstream of AUG

Genetic evaluation of a family with a history of hereditary anemia reveals a point mutation in B(beta) globin gene which results in replacement of Guanina(G) by Cytosine(C) in the B globin chain mRNA molecule 3 bases upstream from AUG codon. Which of the following is likely impaired in this patient?

A. mRNA binding to ribosomes
B. translocation during translation
C. peptide bond formation
D. termination of polypeptide synthesis
E. protein targeting

please explain your answers too.
thanks in advance
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Old 06-10-2012
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I understand from the question that the mutation affects the 5' Cap of the mRNA as it is found upstream of the start codon AUG.
It also contains 7methyG residues so it makes sense that the G was replaced by something.
The functions of the capping is mainly to protect the mRNA from degradation and extend its half life as well as some help with translocation of the mRNA from the nucleus. i couldnt find any answer who matched this options so i must assume that it also plays a role in the binding of ribosome to mRNA so i might go with answer A.

Translocation during translation i understand it probably means the cotranslation which happens when a protein is syntesized into the rER.
it needs the SRP which is not associated with the c terminal

please let us know what is the answer
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Old 06-10-2012
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I will go with A too because transcription is impaired .....the only that implies transcription is A.
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Old 06-10-2012
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Quote:
Originally Posted by modesty View Post
I understand from the question that the mutation affects the 5' Cap of the mRNA as it is found upstream of the start codon AUG.
It also contains 7methyG residues so it makes sense that the G was replaced by something.
The functions of the capping is mainly to protect the mRNA from degradation and extend its half life as well as some help with translocation of the mRNA from the nucleus. i couldnt find any answer who matched this options so i must assume that it also plays a role in the binding of ribosome to mRNA so i might go with answer A.

Translocation during translation i understand it probably means the cotranslation which happens when a protein is syntesized into the rER.
it needs the SRP which is not associated with the c terminal

please let us know what is the answer
yes, the answer is A but the explanation they have given in uworld is so not understandbale. they talk about some Kozak sequence which i've never heard of before! I wish i cud copy n paste their explanation here! May be you can check it for urself. Question ID is 2086
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Quote:
Originally Posted by rapiddo View Post
I will go with A too because transcription is impaired .....the only that implies transcription is A.
why would you say transcription is impaired? you dont need mRNA binding to ribosomes for transcription, rather that is for translation
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I have checked about the kozak segment in wikipedia i understood that is actually found 3 N upstream of AUG so it seems they were speaking about it. it says that it plays a major role in initiation of translation.

But i have also found that the 5cap is the one who actually binds the mRNA to the ribosome and not the kozak segment.

Anyhow it seems like another low yield or WTF question that you need to get in order to get 280.
Thank for the answer.
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Quote:
Originally Posted by numbndumb View Post
why would you say transcription is impaired? you dont need mRNA binding to ribosomes for transcription, rather that is for translation
My bad Thanks for the correction.
Its not transcription that is impaired, rather it is the post transcriptional process that has a fault since the mutation is in the mRNA.
Thanks to modesty for the explanation.
Since post transcription precedes translation,that makes A correct since translation indicates mRNA binding to ribosomes.
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Old 07-30-2012
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B thal, is associated with splice some defect, promoter sequence defect, or kozak sequence defect.
kozak is 3 bases away from AUG, it has a role in the binding of mRNA to the ribosomes, and may lead to thalassemia intermedia.
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