nucleotides qustion

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Erised
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nucleotides qustion

Post by Erised » Wed Nov 02, 2005 4:09 pm

Hey all!
Well I just had a test on DNA, and I have no idea how I did but there is a question which I have serious doubt about.
The set of questions was about what causes sickle cell anemia. Well, I think I got the part right about which nucleotide was substituted in the DNA, but there were two other questions:

If the gene is 150 amino acids long, and the wrong amino acid was put on the seventh gene, which nucleotide was substituted?
* I got the answer 20. I'm sure it's 20 but I'm totally new to this :? Anyone know if it's right?

And another question was
How many nucleotides are in this gene?
*Well, I figured that since there are 150 amino acids, and 3 anticodons that code for amino acids, then it's 150*3=450.


Does it look right? I don't even know if I understood the question correctly :?

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Morris
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Post by Morris » Wed Nov 02, 2005 5:45 pm

The second answer is right: every codons encodes for an AA, then 150*3=450

Is the first question that i can't understand: if you speak about genes I think you must speak about nucleotides not aminoacids; a protein is composed by aminoacids not a gene. And what means seventh gene?
The cell sickle anemy if I'm not wrong, it's the swap of nucleotides A and T; one of them passes form the stamp strand, to the encoding strand: for it DNA doesn't encodes for valine, but for glutammic acid (or aspartic), that has a longer chain.

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canalon
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Post by canalon » Wed Nov 02, 2005 6:25 pm

I guess that it should be on the "seventh amino acid" rather than gene. Then the mutation should be on the 19, 20 or 21st nucleotide. Considering that a mutation on the 3rd nucleotide is less likely to generate a mutation, nucleotide 19 or 20 are more likely to be involved. If you know which Amino acid change caused tour mutation, you could easily figure out the good one with a genetic code table.
Patrick

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)

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