Lesson Video 4-9

ArielM
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Joined: Mon Oct 02, 2017 9:15 pm

Lesson Video 4-9

Postby ArielM » Wed Dec 13, 2017 7:52 pm

Hey,

What is going on at the end of slide four in Lesson Video 4-9? Dr. Anthony was saying something important and then the video cut off right before he was about to talk about missense mutations. What was he going to say?

Sincerely,
-Ariel M.
NS_Tutor_Andrew
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Re: Lesson Video 4-9

Postby NS_Tutor_Andrew » Thu Dec 14, 2017 1:30 pm

Hi Ariel,

I believe the point is that missense mutations are worth paying particular attention to because the details of the mutation allow you to predict the effect that it will have. A conservative mutation, in which an AA is replaced by another AA with similar properties, is less likely to alter the function of a protein than a nonconservative mutation, which would replace an AA with one that has different properties (like replacing alanine with glutamic acid). The MCAT likes to test this by asking which of a set of 4 possible mutations would most or least disrupt the function of a given protein (or of a certain area of a protein, like the active site of an enzyme).

Thanks for pointing this out, and we'll make a point to fix the video!
Andrew D.
Content Manager, Next Step Test Prep.
ArielM
Posts: 33
Joined: Mon Oct 02, 2017 9:15 pm

Re: Lesson Video 4-9

Postby ArielM » Thu Dec 14, 2017 6:23 pm

Hi Andrew,

Thank you for your explanation. So just answer the hypothetical MCAT question: Would the non-conservative missense mutations be the most likely to disrupt protein function (at an enzyme's active site) because this type of mutation literally codes for another amino acid- and thus, essentially changes the structural and functional properties of the protein itself- and the silent mutations be the least likely to disrupt protein function, because they could occur without altering the properties of the protein?

Sincerely,
-Ariel M.
NS_Tutor_Andrew
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Re: Lesson Video 4-9

Postby NS_Tutor_Andrew » Mon Dec 18, 2017 11:50 am

Hi Ariel,

Almost! A few extra things should be considered, though. First, nonsense mutations are likely to have a very dramatic impact on protein function because they literally truncate it. If you have an anomalous residue, it's possible that the protein can "work around" that, so to speak, but if a sizable part of the protein is missing, that's almost guaranteed to drastically affect three-dimensional folding and overall functionality.

Also, within missense mutations, don't forget that both nonconservative and conservative mutations code for different amino acids.To get the hang of the difference between conservative and nonconservative mutations, imagine this analogy. It's not particularly realistic but I think it's intuitive and captures the difference. Imagine you're taking a biochemistry course in college, and in some weird turn of events, someone takes away your textbook and you have to replace it by reaching into a box that contains a bunch of different books and randomly picking one. If you were to randomly pick out another biochemistry textbook by a different author, that'd be a little bit awkward because there might be some non-overlap in terms of the HW, but you could still use it to study the same basic material. That's kind of like a conservative mutation -- it's a different amino acid, but a similar one. The function might not be exactly the same, but it's still within the same ballpark. On the other hand, if you were to pick out a Harry Potter book, you'd be out of luck for your biochem coursework. That's more like a non-conservative mutation -- it's a totally different amino acid with different properties, and it's likely to impede the proper function.

But yes, silent mutations would be the least likely to affect protein function.

Of course, in reality, biology is messy and you have to do experiments and/or complex simulation to really be able to figure out the effects of various mutations, but the above line of reasoning is the predictive power you'd need for the MCAT.

Hope this helps!
Andrew D.
Content Manager, Next Step Test Prep.
ArielM
Posts: 33
Joined: Mon Oct 02, 2017 9:15 pm

Re: Lesson Video 4-9

Postby ArielM » Wed Dec 20, 2017 12:48 am

Thank you, Andrew. You always provide such thorough responses.

Sincerely,
-Ariel Morrow
NS_Tutor_Andrew
Site Admin
Posts: 289
Joined: Mon May 23, 2016 1:47 pm

Re: Lesson Video 4-9

Postby NS_Tutor_Andrew » Wed Dec 20, 2017 6:56 pm

Hi Ariel,

You're very welcome! Glad to be of help, and please keep up the great questions!
Andrew D.
Content Manager, Next Step Test Prep.

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