Lesson 7, Video 5, Slide 9 (last slide) - Amino Acids

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Chengsolomon
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Joined: Tue Jan 30, 2018 1:23 pm

Lesson 7, Video 5, Slide 9 (last slide) - Amino Acids

Post by Chengsolomon » Thu Feb 22, 2018 6:16 pm

I understand Cysteine and Tyrosine are polar and non-polar, respectively. However, the abovementioned part of the online MCAT video say otherwise. Kindly clarify.

Thanks!
Cheng
NS_Tutor_Andrew
Posts: 520
Joined: Mon May 23, 2016 1:47 pm

Re: Lesson 7, Video 5, Slide 9 (last slide) - Amino Acids

Post by NS_Tutor_Andrew » Fri Feb 23, 2018 7:57 pm

Hi Cheng,

Yes, you're basically right, although cysteine and tyrosine are both interesting molecules in terms of polarity. For cysteine, the S-H bond actually falls below the threshold usually used to define polar covalent bonds, with an electronegativity difference of 0.38, but it is usually considered as polar due to its ability to participate in hydrogen bonding. Likewise, tyrosine is usually considered nonpolar because its large aromatic ring in the side chain "outweighs" the polar -OH group. We'll make it a top priority to fix this.

Thanks for the question!
Andrew D.
Content Manager, Next Step Test Prep.
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