UWorld question (spoiler)- pKa values for amino acids???

[dangit]

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This is in regards to UWorld Question ID 12347


Basically, the question is asking if you can recall the pKa values of different amino acids. I thought USMLE wouldn't ask questions like these... wtheck...

They show a titration curve and you have to match the pKa values to the correct amino acids. uh.... i don't see this anywhere in FA.

 

[SlaveOfTCMC]

reach back to your college biochemistry course

or at least reach back to your knowledge of polar (acidic or basic) side groups

If the USMLE does ask this, it's not because they want you to memorize pKa values, but rather to understand the concept that 3 pKa points means its side chain is charged, and thus know that a very low first pKa means that the side chain is more acidic (glutamic acid or aspartic acid)

 

[fuzzywuz]

I just had a question that asks you to find the net charge of lysine in a given pH.

So I guess they do want us to memorize pKas.

 

[ATrim7]

I just had a question that asks you to find the net charge of lysine in a given pH.

So I guess they do want us to memorize pKas.

If I get asked a question like that on the real deal I'm choosing C and moving on. They can have that one point.

 

[fahimaz7]

I didn't have a single pk value question on my test.

 

[jfgavina]

When I saw this question in UW I started to fibrillate, horrible LOL

 

[Celestine]

When I saw this question in UW I started to fibrillate, horrible LOL

Ugh, me too. Like c'mon UWorld, I know you're trying to challenge us and make us learn, but memorizing pKas? That's the definition of useless and low yield...

 

[tco]

Just realize how many protons can be added to the amino acids. That'll narrow it down to at least 50%. They're probably always going to include His in the group, which has a protonatable group at a pKa of 6. If it's not at 6, you know it's not His. After that, just take a guess if you're not sure.

 

[MrAgreeable]

I will channel my inner HS football days and punt this question, tip my hat to the test writers, and come to terms with the fact that they burnt me on one.