Polar Acidic and Basic Amino Acids

[@friedchicken_legs2866]

thank you Leah! I've been studying these things for years but they never made any sense to me until you explained it. Bless your kind soul for sharing these videos for free

[@Leah4sciMCAT]

Awwww, you're so welcome!

[@AdamuAbdi-i5r]

So interesting lesson

[@Leah4sciMCAT]

Glad you enjoyed it!

[@madelinecaymo5118]

Thank you for sharing your knowledge. I've been really having a hard time in my BioChem class. You helped a lot.

[@Leah4sciMCAT]

Happy to help!

[@michellecobos45]

7:00 you say that tyrosine is overall hydrophobic (nonpolar ) then how come it’s included in this video of polar aa-sorry im just co fused

[@Leah4sciMCAT]

There's no hard line between hydrophobic and hyrophilic. Some can be in between where they are very very mildly soluble in water. Tyrosine is mostly hydrophobic due to the benzene ring but is slightly more agreeable in water than say phenylalanine due to having an OH group. If Tyrosine is deprotonated the negative charge makes it more water soluble

[@lihuic]

At 4:28 you mentioned Cystine is not quite acidic or basic but at high enough conditions we do have an ionisable group, giving us an S minus which is hydrophilic. What is defined as high? High temperature? Thanks

[@Leah4sciMCAT]

pH conditions

[@ugazbethebest8]

Are all the nitrogen atoms in Arginine essentially sp2 hybridized? And without resonance, would those nitrogens considered sp3?

[@Leah4sciMCAT]

Great question! Yes, because of resonance, all the nitrogen atoms in arginine are considered to be sp2 hybridized. Without consideration of that resonance, just going on the number of bonding and non-bonding electrons, two of those nitrogens would be sp3.

[@lihuic]

You mentioned that histidine has a PKa of 6 but it is a basic amino acid!

[@Leah4sciMCAT]

it's not about the pH as much as what happens to the proton. If the amino acid GRABS a proton it's acting as a base. If it donates a proton it's acting as an acid. Histidine grabs a proton. see this for review: leah4sci.com/arrhenius-bronsted-lowry-and-lewis-acids-and-bases-in-organic-chemistry/

[@mhtsos127]

Why the -COOH of cystein is more acidic than serin, since O is more electronegative than S ??

[@Leah4sciMCAT]

at which specific point in the video?

[@mhtsos127]

Leah4sciMCAT it is not in the video.It's a general question. I think its because of the hydrogen bonds endomolecular in serine but i am not sure this is the correct answer

[@angelghaemi]

hi leah! you said in the video that cysteine and threonine can be classified as nonpolar or polar/hydrophobic or hydrophilic. but what does the mcat classify this as? thanks!

[@Leah4sciMCAT]

The MCAT won't ask a simple 'is this hydrophobic' type question. Instead they'll ask about the chemistry behind it, for example the chains ability to interact in a certain environment, or worse, how a mutation swapping a very reactive side chain for this one will impact its active site or similar

[@CH-nz5vh]

great videos!! you are awesome!

[@Leah4sciMCAT]

Thank you

[@beckygoertzen5447]

bless you

[@Leah4sciMCAT]

Awww thanks so much!

[@moaadbakken5591]

I think of it as aspardick acid and that gives me the D XD awesome vid btw

[@garretjcoleman]

Not sure she meant it that way but that's what I heard too. Even had to rewind to make sure that's what she said lol.

[@warpath7985]

I just heard it and was laughing to myself. Came to the comments to see if anyone else noticed lol.

[@Leah4sciMCAT]

the funnier, weirder or dirtier the mnemonic, the more likely you are to remember something

[@Leah4sciMCAT]

Yup, that IS what I said 😉

[@Eric-sq4hd]

You're a boss.

[@Leah4sciMCAT]

You know it!