AAMC Sample Test C/P #49 & #50

[premed1244]

Hi all,

Just took my first practice exam, and had a question on these two.

#49: The stabilization of pantothenate [which has a COOH] in PanK3 [an enzyme] is most likely due to an active site:

A) Arginine
B) Asparagnine
C) Aspartate
D) Glutamine

I chose A because I figured its' positive charge would stabilize the negative charge of pantothenate. Instead, the given answer was C.

And then for #50:
The amino acids Asp6, Asn9, Thr10, His11, and Arg27 are found near the ADP binding site of PanK3. Which two amino acids contribute to the stabilization of ADP binding described in the passage?
A: Asn9 and Thr10
B: His11 and Arg27
C: Asp6 and Arg27
D: Asp6 and His11

The answer was B here. So in #49 a negative charge is stabilized with an acidic AA, but in #50 a negative charge is stabilized with two basic AAs. What gives?

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[aalamruad]

Hi all,

Just took my first practice exam, and had a question on these two.

#49: The stabilization of pantothenate [which has a COOH] in PanK3 [an enzyme] is most likely due to an active site:

A) Arginine
B) Asparagnine
C) Aspartate
D) Glutamine

I chose A because I figured its' positive charge would stabilize the negative charge of pantothenate. Instead, the given answer was C.

And then for #50:
The amino acids Asp6, Asn9, Thr10, His11, and Arg27 are found near the ADP binding site of PanK3. Which two amino acids contribute to the stabilization of ADP binding described in the passage?
A: Asn9 and Thr10
B: His11 and Arg27
C: Asp6 and Arg27
D: Asp6 and His11

The answer was B here. So in #49 a negative charge is stabilized with an acidic AA, but in #50 a negative charge is stabilized with two basic AAs. What gives?

If I remember that passage correctly, you need to read the last few sentences of the passage to get that first question right. It says something about aspartate stabilizing the enzyme, I believe. Tough question, I missed it too

 

[Nucleophile1]

Hi all,

Just took my first practice exam, and had a question on these two.

#49: The stabilization of pantothenate [which has a COOH] in PanK3 [an enzyme] is most likely due to an active site:

A) Arginine
B) Asparagnine
C) Aspartate
D) Glutamine

I chose A because I figured its' positive charge would stabilize the negative charge of pantothenate. Instead, the given answer was C.

And then for #50:
The amino acids Asp6, Asn9, Thr10, His11, and Arg27 are found near the ADP binding site of PanK3. Which two amino acids contribute to the stabilization of ADP binding described in the passage?
A: Asn9 and Thr10
B: His11 and Arg27
C: Asp6 and Arg27
D: Asp6 and His11

The answer was B here. So in #49 a negative charge is stabilized with an acidic AA, but in #50 a negative charge is stabilized with two basic AAs. What gives?

For #49, at the bottom of the passage, it talks about PanK3 being stabilized by a carboxylate group. Aspartate is the only one listed with a carboxylate group.

For #50, the question stem asks which amino acids contribute to the stabilization of ADP binding. Since ADP is negatively charged, you would want positively charged amino acids. B is the only answer with two positively charged amino acids.

 

[premed1244]

Thanks you both, guess I should have read more carefully!

 

[ScrubswithnoSleeves]

So I get that the passage said that the carboxylate group in the active site stabilizes the binding of pantothenate, but can someone explain to me why that is? I've attached a screenshot of pantothenate from this passage.

I also missed this one because I put arginine.

 

[Ro300!]

So I get that the passage said that the carboxylate group in the active site stabilizes the binding of pantothenate, but can someone explain to me why that is? I've attached a screenshot of pantothenate from this passage.

I also missed this one because I put arginine.

I realize my response is a little late but hope it'll help someone who may have the same question in the future. The last paragraph states "...binding is stabilized by interactions between C2' and C4' hydroxyl groups of pantothenate...." I'm not exactly sure of the mechanism that occurs but something in the line of a hydrogen bond between the carboxylate and -OH seems plausible (since carboxylate, being more stable due to its resonance, will confer this stability to -OH).