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  #1  
Old 07-31-2011
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I disagree UWorld question..are you serious?

Ok, so I came across this question while doing UW and I got it right but after reading the explanation I was just like

The question shows the titration curve for an amino acid & asks us which amino acid is it. The explanation states that since there are three different pKa's the amino acid must have three titratable protons - histidine, arginine, lysine, aspartic acid, glutamic acid, cysteine & tyrosine. It then states that the pKas of histine are 1.8, 6 & 9.2 which is the most consistent with the graph shown and is the correct answer.

DO WE HAVE TO KNOW THE pKa's ?!
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  #2  
Old 07-31-2011
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Quote:
Originally Posted by Hope2Pass View Post
Ok, so I came across this question while doing UW and I got it right but after reading the explanation I was just like

The question shows the titration curve for an amino acid & asks us which amino acid is it. The explanation states that since there are three different pKa's the amino acid must have three titratable protons - histidine, arginine, lysine, aspartic acid, glutamic acid, cysteine & tyrosine. It then states that the pKas of histine are 1.8, 6 & 9.2 which is the most consistent with the graph shown and is the correct answer.

DO WE HAVE TO KNOW THE pKa's ?!
hahahahahahahaha....this question sucks!
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  #3  
Old 07-31-2011
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@hope2pass: Is the answer histidine?
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  #4  
Old 07-31-2011
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Originally Posted by usluipek View Post
@hope2pass: Is the answer histidine?
Yup, the answer is Histidine.

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Originally Posted by bebix View Post
hahahahahahahaha....this question sucks!
Yeah, tell me about it. I was so ridiculed after reading the explanation haha It was a total fluke I got it right
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  #5  
Old 07-31-2011
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Quote:
Originally Posted by Hope2Pass View Post
Ok, so I came across this question while doing UW and I got it right but after reading the explanation I was just like

The question shows the titration curve for an amino acid & asks us which amino acid is it. The explanation states that since there are three different pKa's the amino acid must have three titratable protons - histidine, arginine, lysine, aspartic acid, glutamic acid, cysteine & tyrosine. It then states that the pKas of histine are 1.8, 6 & 9.2 which is the most consistent with the graph shown and is the correct answer.

DO WE HAVE TO KNOW THE pKa's ?!
yup u are right histidine is one of positively charged amino acid with three pka's and histine is required for N.O synthesis by nitric oxide synthase ...
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  #6  
Old 06-19-2012
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Default answer please

do we have to know the pkas of the aminoacids???!!!
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  #7  
Old 06-19-2012
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I dont think so.

I've heard on the actual exam they are always blah questions which no normal person is able to answer.

They may be part of the experimental pool , they may be suckers to make you panic, throw you off track .. make you confused.

Ignore them and move on. This seems like one in a million questions.

I doubt if i would lose sleep over this blah ,and no one else should either.
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  #8  
Old 06-19-2012
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Idea!

yup... the Q looks pretty absurd... but, we dont need to know the pKa's to answer this Q.... i think the take home point is-just know the amino acids with 3 titrable protons and here's how i see it ....

the basic (HLA) ones- Histidine, Lysine, Arginine
the acidic ones - aspartate, glutamate
just 2 more... cysteine and tyrosine....
"acidic basic CT"
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  #9  
Old 06-19-2012
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I had this question too. My reaction was wtf... lol..
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  #10  
Old 06-20-2012
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They cant let you get all the questions right, can they?

So that's one question to make sure you dont :P
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  #11  
Old 06-20-2012
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i remember this question, it's one of three questions in UW i didnt even try with.
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  #12  
Old 05-20-2014
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Hahahaha. Just had this question and had to google it. Your responses made me feel better!
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  #13  
Old 05-20-2014
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Quote:
Originally Posted by phlebgirl View Post
Hahahaha. Just had this question and had to google it. Your responses made me feel better!

Just cram that question Guys !!! ;D when i saw that at my time, i was like, what IS This?? just memorize the concept , just in case you get a similar question like this in exam.. if
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Old 05-20-2014
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Default

Quote:
Originally Posted by Hope2Pass View Post
Ok, so I came across this question while doing UW and I got it right but after reading the explanation I was just like

The question shows the titration curve for an amino acid & asks us which amino acid is it. The explanation states that since there are three different pKa's the amino acid must have three titratable protons - histidine, arginine, lysine, aspartic acid, glutamic acid, cysteine & tyrosine. It then states that the pKas of histine are 1.8, 6 & 9.2 which is the most consistent with the graph shown and is the correct answer.

DO WE HAVE TO KNOW THE pKa's ?!

LOL I remember this question well, I also thought the same as you when reading it the first time, but then when you read the explanation you see that you can deduct this if you know which aa have different pKa's and are titratable, so no need to know the exact pKa's there.
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Old 10-03-2014
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Default thank God!!

thanks to this post...
it saved my life
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  #16  
Old 02-18-2015
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Default Awful question

I had this question yesterday and after reading the explanation I was like "WTF are you serious?" like my test is around the corner and this type of question serves only one purpose: to freak you out. I'm glad I'm not the only one who thought it was crazy.
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  #17  
Old 03-20-2017
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sHi guys,

If you get this question, knowing acidic and basic amino acids helps... but I got it wrong. So I learned

pH - concentration of ions
pKa - strength of acid
Titratable proton - Proton that can be lost when an acid and base collide with each other

Higher the pka, the stronger the acid (lower pH)
Lower the pKa, the weaker the acid (higher pH)

Only histidine is listed from one of the 7 AA that have titratable protons. Remember that Histidine has a net zero charge at body pH but it has 3 POTENTIALLY titratable protons. Should one of these protons dissociate, it give histidine an ionic charge and it spills out into the blood due to ionic concentrations gradients. In addition, those H protons that dissociate wreak havoc on body systems and induce the clinical manifestations that are seen in histidinemia (HISTIDASE deficiency in sub asian pop causes buildup of AA in blood) . The graph shows gradual addition of a base which causes titration of the proteins at different pKA values (values of pka are not important but the concept is as this concept can be used in many acid base balance disturbances scenarios)
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Last edited by 250orbust; 03-20-2017 at 03:43 AM. Reason: spelling
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