berkeley review genetics/sickle cell passage

[Mr Brain]

I'm having a hard time with question #2 in BR Biology II, p. 329. how do you know that valine reaches pI later than glutamate unless you know the exact pKa values for each of ionizable hydrogens on each amino acid?

confused...

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[jpatel]

I'm having a hard time with question #2 in BR Biology II, p. 329. how do you know that valine reaches pI later than glutamate unless you know the exact pKa values for each of ionizable hydrogens on each amino acid?

confused...

I dont have the book and dont know what question your talking about.

But I do know that glutamate would have lower pI than valine.

valine has 1 amino grp and 1 carboxylic so its pI would be around 6 ( just guessing). In a sense, at pH 6 all amino grp will be protonated with a + 1 charge and all carboxylic grp will be deprotonated with -1 charge. Thus, net charge = 0

glutamate has 1 amino grp and 2 carboxylic. its more complicated because you want all amino grp to be protonated with + 1 charge and only 1/2 of carboxylic group to be deprotonated. SO that net charge would be 0. THink hard about what i mean here. Since I only want 1/2 carboxylic grp deprotonated vs all in valine, I must lower pH furthur. glutamate pI should be around 4.5 ( just guessing)

 

[traitorman]

glutamate is one of the acidic proteins and thus has 3 pkas. Because it is more acidic, its pI will be more acidic (less than 7) compared to the pI's of other amino acids.

Likewise, the basic amino acids have 3 pkbs and will have a pI more basic (greater than 7) compared to other amino acids.