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Chapter 12: Biological Molecules

Re: Chapter 12: Biological Molecules

Postby goldstanda3269 » Fri Jul 16, 2021 7:30 pm

horbowiec.7527 wrote:Re ORG CHM Chapter 12 Question 3 (ORG-279):

Worked solution mention Aspartic Acid (D) and Glutaminic Acid (E) but none of the answer choices have that, is it a typo in answer choice A and it should be D-E or E-D? And that is correct answer?


Those were quite reasonable suppositions! However, it is just that the worked solution was not clear enough, here is the improvement:

In a basic (alkaline) solution (e.g., pH of 12), acidic protons will be removed. Glycine (G) is neutral (i.e. according to Figure 2, G does not have an acidic side chain); however, Aspartic Acid (D) has a COOH group as a side chain (Figure 2) which can be deprotonated and thus the dipeptide would be negatively charge. Note that the only 2 amino acids with -COOH side groups are D and E (Glutamic Acid); however, E is not among the answer choices so the answer must be answer choice A. Also note that D and E are the only amino acids with the word "acid" in their names.

From Figure 2:

W: tryptophan
K: lysine
Q: glutamine
N: asparagine
P: proline
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Re: Chapter 12: Biological Molecules

Postby horbowiec.7527 » Fri Jul 16, 2021 9:51 pm

Re Q15 & 16:

They both have the exact same worked solution, could I please ask for the update?

Regards,
Ania
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Re: Chapter 12: Biological Molecules

Postby goldstanda3269 » Sat Jul 17, 2021 1:20 am

horbowiec.7527 wrote:Re Q15 & 16:

They both have the exact same worked solution, could I please ask for the update?


Actually, the Question 16 worked solution is there but, you are correct to say that Question 15 is duplicated (this will be corrected on Monday).

You will be able to find all of the Chapter 12 worked solutions from Question 1 to 34. The duplicated Question 15 issue seems to be preventing Question 35 from showing, but that will be resolved on Monday.
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Re: Chapter 12: Biological Molecules

Postby horbowiec.7527 » Sat Jul 17, 2021 12:35 pm

Thank you, the explanation for question 3 is now crystal clear!

I also wanted to flag Q11 (ORG-281) as worked solution doesn't explain it, seems like that explanation is the same as for question 31 (ORG-290)...
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Re: Chapter 12: Biological Molecules

Postby goldstanda3269 » Sat Jul 17, 2021 2:43 pm

horbowiec.7527 wrote:I also wanted to flag Q11 (ORG-281) as worked solution doesn't explain it, seems like that explanation is the same as for question 31 (ORG-290)...


Correct! We will have that repaired early next week. Keep up your productive weekend!

You are early and you have advanced extremely well. Hopefully, you have been taking very brief notes and that you study from those notes, from the beginning, at least every weekend. Such a procedure is so important so that what you learn from practice problems today will not be forgotten approx. 2 months from now! :)
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Re: Chapter 12: Biological Molecules

Postby horbowiec.7527 » Sat Jul 17, 2021 5:15 pm

Thank you, that is very kind of you too say:) Although I don't feel I'm that early, I feel time is getting away from me too quickly...
Trying to keep my notes brief but it is a lot!

Another question if I may (as this is an important topic), Re Q23:
I chose correct answer here but not sure if my reasoning was correct after reading worked solutions.

I assigned Z to right double bond because 2 substituents in the right ring are coming towards me (black triangles) = Z or cis. And I assigned Z to left double bond because 2 substituents in left ring are coming into the page (dashed triangles) = Z or cis. I didn't consider H as its in the middle between 2 rings. Is my reasoning correct here, since substituents are not directly attached to double bonds? I don't quite understand the last summary sentence in worked solutions regarding this Q.

Regards,
Ania
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Re: Chapter 12: Biological Molecules

Postby goldstanda3269 » Sat Jul 17, 2021 8:22 pm

horbowiec.7527 wrote:Thank you, that is very kind of you too say:) Although I don't feel I'm that early, I feel time is getting away from me too quickly...
Trying to keep my notes brief but it is a lot!


Unfortunately, for most people, this is not the kind of exam that you will feel 'ready' for! Most successful students never feel comfortable with their preparation and yet can still achieve their dreams.

Please consider reading: https://www.gamsat-prep.com/gamsat-stud ... nal-notes/


horbowiec.7527 wrote:Another question if I may (as this is an important topic), Re Q23:
I chose correct answer here but not sure if my reasoning was correct after reading worked solutions.

I assigned Z to right double bond because 2 substituents in the right ring are coming towards me (black triangles) = Z or cis. And I assigned Z to left double bond because 2 substituents in left ring are coming into the page (dashed triangles) = Z or cis. I didn't consider H as its in the middle between 2 rings. Is my reasoning correct here, since substituents are not directly attached to double bonds? I don't quite understand the last summary sentence in worked solutions regarding this Q.


Somewhere you correctly doubted your reasoning because of one key point: In both of your cases, you were looking at carbons that are not involved in the double bond. Also, you were thinking about Z and E with respect to the ring, which is fine and a good skill to have because you may be confronted with such questions, however, this problem specifically asked for Z and E with respect to the double bond so the carbons you were looking at are not specifically included in this analysis.

To get your eyes oriented to that double bond, you may want to look at ORG 2.2.1 again, and also the nomenclature exercises for Chapter 4.

And finally, consider going to time code 4:04:37 to 4:07:55 of the following video:

https://www.members.gamsat-prep.com/_me ... =209123256 (if it starts too basic, you can increase the speed of the video)
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Re: Chapter 12: Biological Molecules

Postby horbowiec.7527 » Sun Jul 18, 2021 9:18 pm

All very very helpful, thank you!

Regards,
Ania
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Re: Chapter 12: Biological Molecules

Postby penguin7 » Sat Jan 01, 2022 9:52 am

Dear GS, for Question 34, the Correct Answer at the header needs to align with the Correct Answer in the Worked Solutions.
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Re: Chapter 12: Biological Molecules

Postby goldstanda3269 » Sat Jan 01, 2022 5:00 pm

penguin7 wrote:Dear GS, for Question 34, the Correct Answer at the header needs to align with the Correct Answer in the Worked Solutions.


The correct answer is D. This will be updated by Monday. Happy New Year!
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Re: Chapter 12: Biological Molecules

Postby ohwaseng8484 » Wed Jan 05, 2022 11:10 pm

Hi, will like to ask on Chpt 12 Qns 13. Omega-6 fatty acids are those with double bond on the 6th carbon from CH3 end. May I ask why Lenolenic acid isnt considered an omega 6 acid? Thanks
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Re: Chapter 12: Biological Molecules

Postby goldstanda3269 » Sat Jan 08, 2022 1:14 pm

ohwaseng8484 wrote:Hi, will like to ask on Chpt 12 Qns 13. Omega-6 fatty acids are those with double bond on the 6th carbon from CH3 end. May I ask why Lenolenic acid isnt considered an omega 6 acid? Thanks


Good question!

First, none of the answer choices is zero. This means that there MUST be at least one omega-6 fatty acid. Let's see what we can learn from the results.

Here is the clue: Notice that you likely counted linoleic acid as omega-6 even though it also has a double bond at omega-9. Likewise, you likely counted arachidonic acid, with its four double bonds, as omega-6, thus the other double bonds were also 'ignored'. So we do have a pattern: omega counts the first carbon's double bond from the methyl end.

And so, we come to linolenic acid: although it does have a double bond at the 6th carbon from the methyl end, if we are to follow the only other two confirmed examples, linolenic acid must be an omega-3 fatty acid.

This was not an easy question!
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Re: Chapter 12: Biological Molecules

Postby rockypatel8090 » Sat Feb 26, 2022 10:16 pm

CH12 - Q9 about how many tripeptides can be produced with combo of F D P.
Wouldn't the answer be 3? (not a option)

1) F D P (unique)
2) F P D (unique)
3) P D F (isn't this repeating? same as 1) F D P but reversed?)
4) P F D (unique)
5) D F P (isn't this repeating? same as 4) P F D but reversed?)
6) D P F (isn't this repeating? same as 2) F P D but reversed?)

Does writing in reverse makes the property of peptides any different?
Sorry for my ignorance, not good at Bio.
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Re: Chapter 12: Biological Molecules

Postby goldstanda3269 » Sun Feb 27, 2022 12:13 pm

rockypatel8090 wrote:CH12 - Q9 about how many tripeptides can be produced with combo of F D P.
Wouldn't the answer be 3? (not a option)

1) F D P (unique)
2) F P D (unique)
3) P D F (isn't this repeating? same as 1) F D P but reversed?)
4) P F D (unique)
5) D F P (isn't this repeating? same as 4) P F D but reversed?)
6) D P F (isn't this repeating? same as 2) F P D but reversed?)

Does writing in reverse makes the property of peptides any different?
Sorry for my ignorance, not good at Bio.


There are many Bio students who have the same issue with this type of question.

ORG 12.1, 12.2 and the passage that precedes this question all mention the amino end (N terminal) and the carboxyl end (C terminal) of amino acids and that those ends connect with other amino acids to form peptides/proteins. Think of the 2 ends as your left and right hand. If you shake hands (or "connect") with someone with your left hand, it is simply different from connecting with them with your right hand. The strength is different, your body may turn a bit in a different direction, etc. It is the same with amino acids.

The 3 molecules that you described are not reversed, rather, they are truly different molecules with fundamentally different connections which can result in very different chemical reactions or bonding with receptors or antibodies, etc. Any letter in your list at the start has a free amino end, but if that letter is at the other end, it has a free carboxyl end. That same amino acid would clearly react differently depending on what end is available.
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Re: Chapter 12: Biological Molecules

Postby rockypatel8090 » Wed Mar 02, 2022 8:15 pm

Okay good to know, thank you :)
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