Question on AAMC Practice full length 1 B/B #32

[MC789]

Can someone explain why B can't be the answer. My reasoning was that in the passage, above equation 1, it states that ornithine is an AMINO ACID that is found in cells but NOT INCORPORTATED INTO PROTEINS. I've studied translation a lot and know that for amino acids to be brought in for the corresponding mRNA, codons have to be available. since ornithine is an AMINO ACID, there must be a codon available corresponding to it. So I ruled out A. = how can ornithine be an AA if theres no codon for it?

I chose b because for proteins to be formed, peptide bonds are required between amino acids. so B made sense on why ornithine is not incorporated into proteins.



where am I going wrong with this?

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[humblethinker]

This is one of those questions where I think it makes sense to dissect the way the question stem is phrased and align it with an answer choice that satisifies exactly what the stem is implying. The stem states with emphasis, "the most fundamental reason..." --- this should be a tip not to overinfer what is being asked. This AA is an exception to the standard rule so the question writer is assessing whether or not you understand the normal basic mechanism (this is really all the mcat does but creates complicated novel scenarios to ensure true understanding). Answer choice A is the only option that is directly answering the concept of what the question stem is asking by basically saying "what is a reason there is an AA that is an exception to the rule in living organisms?" Answer choice B is too general and can be applied in multiple situations and therefore does not directly satisfy the specific concept being tested in the question stem.

 

[MC789]

This is one of those questions where I think it makes sense to dissect the way the question stem is phrased and align it with an answer choice that satisifies exactly what the stem is implying. The stem states with emphasis, "the most fundamental reason..." --- this should be a tip not to overinfer what is being asked. This AA is an exception to the standard rule so the question writer is assessing whether or not you understand the normal basic mechanism (this is really all the mcat does but creates complicated novel scenarios to ensure true understanding). Answer choice A is the only option that is directly answering the concept of what the question stem is asking by basically saying "what is a reason there is an AA that is an exception to the rule in living organisms?" Answer choice B is too general and can be applied in multiple situations and therefore does not directly satisfy the specific concept being tested in the question stem.

Hi! thank you for taking the time to reply.. I'm still lost on why A is the answer. I agree with you on making sure to choose a choice that aligns with the question stem. but its also important that the choice aligns with passage info right? passage states that ornithine is an amino acid. so how can A be the answer when ornithine is an amino acid, which requires that it has a codon. how can something that doesn't have a codon in the standard genetic code become an Amino acid? isn't it basic knowledge that a 3 letter codon corresponds to an amino acid?

 

[humblethinker]

Hi! thank you for taking the time to reply.. I'm still lost on why A is the answer. I agree with you on making sure to choose a choice that aligns with the question stem. but its also important that the choice aligns with passage info right? passage states that ornithine is an amino acid. so how can A be the answer when ornithine is an amino acid, which requires that it has a codon. how can something that doesn't have a codon in the standard genetic code become an Amino acid? isn't it basic knowledge that a 3 letter codon corresponds to an amino acid?

ornithine is just an exception to the rule because it does not have a codon.....this is one of those questions that uses an exception to test a basic science concept. Best option in this case is to go through the answer choices and eliminate without overinferring. Remember....the MCAT tests only very basic science concepts but will put them in convoluted passages with a whole bunch of other information to try and see if you really know the foundational science concepts.

 

[MC789]

ornithine is just an exception to the rule because it does not have a codon.....this is one of those questions that uses an exception to test a basic science concept. Best option in this case is to go through the answer choices and eliminate without overinferring. Remember....the MCAT tests only very basic science concepts but will put them in convoluted passages with a whole bunch of other information to try and see if you really know the foundational science concepts.

ah okay! how would I know that this is an exception? is there a way to spot exception questions on the mcat?

 

[BerkReviewTeach]

ah okay! how would I know that this is an exception? is there a way to spot exception questions on the mcat?

Humblethinker has provided an excellent explanation of how to think your way through this question. It is up to you to build to pool of information needed for this question. This is done through practice, though a concerted effort to memorize important packets of information, and through learning from your mistakes.

The best way to spot an exception is to know the rule (or in this case, the amino acids for which we code.) Do you recall ever learning about ornithine as one of the common twenty amino acids we code for? If you have memorized your amino acids for various classes, then ornithine should sound unfamiliar. It is unfamiliar, because we do not have a codon for it. In vivo synthesis would require assembling proteins from the common twenty amino acids.

The passage gives you some of the common amino acids and their categorization.

 

[MC789]

Humblethinker has provided an excellent explanation of how to think your way through this question. It is up to you to build to pool of information needed for this question. This is done through practice, though a concerted effort to memorize important packets of information, and through learning from your mistakes.

The best way to spot an exception is to know the rule (or in this case, the amino acids for which we code.) Do you recall ever learning about ornithine as one of the common twenty amino acids we code for? If you have memorized your amino acids for various classes, then ornithine should sound unfamiliar. It is unfamiliar, because we do not have a codon for it. In vivo synthesis would require assembling proteins from the common twenty amino acids.

The passage gives you some of the common amino acids and their categorization.

that makes sense, thank you!