TPR- O Chem Question

[PinkTootie]

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Which of the following amino acids least contributes to the low isoelectric point ( pI= 4.1) ?

Histidine
Proline
Aspartic Acid
Glutamic Acid

Tell me people what you would pick.

 

[enervate]

Histidine-- it raises the pI.

 

[sshah92]

Which of the following amino acids least contributes to the low isoelectric point ( pI= 4.1) ?

Histidine
Proline
Aspartic Acid
Glutamic Acid

Tell me people what you would pick.

Isn't it proline?! Histidine will raise the pI because it is basic, but I would think for something to have a basic effect would mean it contributes, simply in the opposite direction. Proline on the other hand isn't relevant in calculating the pI.

 

[FeinMS]

Isn't it proline?! Histidine will raise the pI because it is basic, but I would think for something to have a basic effect would mean it contributes, simply in the opposite direction. Proline on the other hand isn't relevant in calculating the pI.

The question asks for LEAST contribution to low PI. That means, as you said, Histidine will contribute to increase PI, making it least contributor to low PI.

 

[sshah92]

Lol then that is a badly written question. In my mind something not contributing wins over something contributing. Technically they all contribute an equal amount -- there's just more acidic compounds than not.

 

[sakabato93]

I'd probably go with proline.

 

[PinkTootie]

I'd probably go with proline.

Exactly- that's what I picked too.

But the "best" answer is histidine since it would do something polar opposite which is raise the pI...

Not sure when to consider "least" meaning not at all.

 

[sakabato93]

Exactly- that's what I picked too.

But the "best" answer is histidine since it would do something polar opposite which is raise the pI...

Not sure when to consider "least" meaning not at all.

Haha, that's pretty frustrating.

 

[enervate]

Not sure when to consider "least" meaning not at all.

When there isn't a value on the opposite side of the spectrum that otherwise affects the overall average.

For example, consider your GPA. Say you have a GPA composed entirely of Bs-- 3.0. You want a higher average. Which does you the least good? As, Bs, or Cs? Obviously getting more Bs doesn't benefit your average any but Cs actually hurt your average.

 

[sakabato93]

When there isn't a value on the opposite side of the spectrum that otherwise affects the overall average.

For example, consider your GPA. Say you have a GPA composed entirely of Bs-- 3.0. You want a higher average. Which does you the least good? As, Bs, or Cs? Obviously getting more Bs doesn't benefit your average any but Cs actually hurt your average.

You're logic is fine, but the bold, just like the main question in this thread, is incredibly awkward phrasing, especially when its easier to use an alternative.

 

[PinkTootie]

You're logic is fine, but the bold, just like the main question in this thread, is incredibly awkward phrasing, especially when its easier to use an alternative.

Agreed.

Half the time what leaves me stumbling around is the question itself.

 

[benjaminl1nus]

This is a terrible question with a terrible answer. I think Proline is fine as an answer, and Histidine could be a good answer as well. But as for the best answer, I honestly don't think this question deserves that.

MCAT test writers know better. TPR, although a great resource, is a little too convoluted for its own good sometimes.