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Old 07-08-2011
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Biochemistry net charge of amino acid

After hydrolysis of the peptide bonds in a short polypeptide, the following amino acid was identified in a solution:

NH2 CH COOH
CH2
CH2
CH2
CH2
NH2

If the PH of the solution is 7.4, which of the following is the most likely net charge of the pictured amino acid?

a.) +2
b.) +1
c.) 0
d.) -1
e.) -2

the answer is b.) can someone please explain because i do not understand
why. Thank you : )

Last edited by chienpolska; 07-08-2011 at 11:53 PM. Reason: CHCH2CH2CH2CH2 should be together
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  #2  
Old 07-08-2011
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Default

H
o
o
c
chch2ch2ch2ch2nh2 should be together sorry for mistakes!
N
h
2
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  #3  
Old 07-09-2011
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-2 Im guessing. The amino acid will not be dissasociated, so it remain as COOH and not COO-. and itl be more lipid soluble. Acids need acidic environment to be lipid soluble..Biochem I think.
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  #4  
Old 07-09-2011
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Default why is it B

You were correct in the first place, the answer is +1 because in physiological pH (7.4) the carboxyl and amino groups of an aminoacid are ionized (that means that COOH actually is COO- and NH2 is NH3+) for that there are three charges here are:
-1 for the terminal COO-
+1 for the terminal NH3
And +1 for the extra NH3 group

So the first two neutralize each other and the net charge is +1 because of the extra amino group. Which makes this a basic aminoacid (Lysine)

Hope I explained myself weel and helped you
Sorry if there are any typos. I'm writting this from my phone :P
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  #5  
Old 07-09-2011
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damn, i read the whole question wrong and answered wrong! though the concept i got! yeah, he's got the concept right !
boy, i feel stupid, hope i dont rush into these mistakes on the exam!

Last edited by bandar; 07-09-2011 at 09:58 AM.
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