BIOCHEM chapter 2 page 25

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sarita0518
Posts: 10
Joined: Fri Feb 22, 2019 3:08 pm

BIOCHEM chapter 2 page 25

Post by sarita0518 » Fri Mar 15, 2019 1:50 am

Hi,

On page 25, it states the cysteine is considered a polar AA because it can participate in Hydrogen Bonding. This confuses me because I understood hydrogen bonding to be between a Hydrogen bound to either N, O, or F interacting with a different N, O or F. Cysteine has just a SH bond. Please clarify.
NS_Tutor_Will
Posts: 395
Joined: Fri May 25, 2018 9:15 am

Re: BIOCHEM chapter 2 page 25

Post by NS_Tutor_Will » Sun Mar 17, 2019 8:44 am

Unfortunately, there's not a whole lot to clarify as this is one of those weird circumstances. Cysteine can hydrogen bond, but the most common atoms to be involved in hydrogen bonds are N, O, and F, as you said. Hydrogen bonding can occur between more atoms, it's just that N, O, and F are the most relevant and common ones to be involved. All H-bonding requires is a hydrogen bound to a very electronegative atom. N, O, and F are the best, but other atoms can fit the bill, too! You don't need to memorize the others, but, yes, it's definitely a good idea to know the properties of cysteine. When the MCAT tests cysteine, it's usually focused more on disulfide bridges, so keep your eye out for those, too.

Good luck!
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