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  #1  
Old 08-17-2011
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Default Biochemistry problem

a gene encodes a protein with 150 amino acids. there is one interon of 1000 bps, 5' untranslated region of 100 and 3' untranslated region of 200 bp. in the final processes mRNA how many bases lie between the start AUG codon and the final termination codon ?
a. 1750
b.750
c. 650
d. 450
e. 150

Answer with explanation please as i am just starting studying biochemistry and wanna put clear concept how to deal with its problem ,, thanks so much for help
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Old 08-17-2011
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Quote:
Originally Posted by menatallah Elgohary View Post
a gene encodes a protein with 150 amino acids. there is one interon of 1000 bps, 5' untranslated region of 100 and 3' untranslated region of 200 bp. in the final processes mRNA how many bases lie between the start AUG codon and the final termination codon ?
a. 1750
b.750
c. 650
d. 450
e. 150

Answer with explanation please as i am just starting studying biochemistry and wanna put clear concept how to deal with its problem ,, thanks so much for help
Coded regions are exons- 150 AA = 450 bps
Introns (spliced in final transcript)-1000bps
5 and 3 untranslated regions = 300bps

If hnRNA is asked then answer will be 1750 because it contains introns and exons and UTR.

But here final mRNA is asked so it will contain only exons , so it's 450bps.
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Old 08-17-2011
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Default not sure

i have tried to wrap my brain around this problem. i have come up with something but i am not sure if it is correct, sorry! it will help if you can post the answer.
anyway this is my postulation: there are 150 amino acids, to make one amino acid (translation) you need one codon. each codon is made up of 3 bases. so now we have 450. thats one possible answer.

they mentioned intron, an intron is of no importance imo to this question, introns are non coding sequences and are left in the nucleus while the mRNA leaves the nucleus. the mRNA i think is what they mentioned has 100 bp at 5' and 200 bp at 3', and i think it should be added to the 450 bps we just got.

so i want to add the 200 and 100 bps with the 450 and i get 750.

i am really NOT certain this even makes any sense, can you pls post the answer.
thanks

Quote:
Originally Posted by menatallah Elgohary View Post
a gene encodes a protein with 150 amino acids. there is one interon of 1000 bps, 5' untranslated region of 100 and 3' untranslated region of 200 bp. in the final processes mRNA how many bases lie between the start AUG codon and the final termination codon ?
a. 1750
b.750
c. 650
d. 450
e. 150

Answer with explanation please as i am just starting studying biochemistry and wanna put clear concept how to deal with its problem ,, thanks so much for help
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Old 08-17-2011
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the question is specifically about the number between the start and stop codons, nothing else. The UNSTRANSLATED regions lie outside this coding region and the question is not about them. Anything upstream from the start codon or downstream from the stop codon is not counted.
By the way I don't think they could ever ask a question about the total length of mature mRNA, because that would include the poly-A tail which is variable in length so there is no way of knowing exactly.
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Old 08-18-2011
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Correct Answer

the answer is 450 as u said .. thx so much for the help
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Old 08-18-2011
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Quote:
Originally Posted by patient doctor View Post
the question is specifically about the number between the start and stop codons, nothing else. The UNSTRANSLATED regions lie outside this coding region and the question is not about them. Anything upstream from the start codon or downstream from the stop codon is not counted.
By the way I don't think they could ever ask a question about the total length of mature mRNA, because that would include the poly-A tail which is variable in length so there is no way of knowing exactly.
that was a question in kaplan lecture notes i don't have idea if it can come or not but it is a good chance to answer question like that so nothing may appear strange in the exam
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Old 08-18-2011
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Correct Answer

Quote:
Originally Posted by nativedoc View Post
i have tried to wrap my brain around this problem. i have come up with something but i am not sure if it is correct, sorry! it will help if you can post the answer.
anyway this is my postulation: there are 150 amino acids, to make one amino acid (translation) you need one codon. each codon is made up of 3 bases. so now we have 450. thats one possible answer.

they mentioned intron, an intron is of no importance imo to this question, introns are non coding sequences and are left in the nucleus while the mRNA leaves the nucleus. the mRNA i think is what they mentioned has 100 bp at 5' and 200 bp at 3', and i think it should be added to the 450 bps we just got.

so i want to add the 200 and 100 bps with the 450 and i get 750.

i am really NOT certain this even makes any sense, can you pls post the answer.
thanks

sure that make sense thanks so much for ur help and u got the right answer thanks alot
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Old 08-18-2011
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If I got this correctly, then simply the protein is 150 aa which is 150 X 3 = 450 bps.

why worry about the rest, the mRNA = the protein.

so my answer is 450 bps. Right?
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Originally Posted by USMLE2011m View Post
If I got this correctly, then simply the protein is 150 aa which is 150 X 3 = 450 bps.

why worry about the rest, the mRNA = the protein.

so my answer is 450 bps. Right?
yes u r so right but i asked for more explanation as i am just begining studying biochemistry and need to make good concept of how to think and solve and they tried to help me by explaning how to do that
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Old 08-18-2011
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Quote:
Originally Posted by menatallah Elgohary View Post
yes u r so right but i asked for more explanation as i am just begining studying biochemistry and need to make good concept of how to think and solve and they tried to help me by explaning how to do that
Yes that is absolutely essential, I just want to be sure if when I say " final processed mRNA is the protein, am I correct guys??
So is my approach to the questions right?
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Correct Answer

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Originally Posted by USMLE2011m View Post
Yes that is absolutely essential, I just want to be sure if when I say " final processed mRNA is the protein, am I correct guys??
So is my approach to the questions right?
yes 100% right u solve it as in kaplan answer he simply multplied as u did 150 x 3
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