Determining the isoelectric point of a polypeptide

This video walks you through my strategy for determining the isoelectic point (or pI) of a small polypeptide, and applies this strategy to an example. You can practice this approach by designing your own polypeptides and check you answer using Thermo-Fisher's peptide analyzer at www.thermofish...

[@tamarkikvidze]

I am jealous of your students! That is a beautiful explanation, thank you so much.

[@carinaashcraft1627]

just watched 3 other vids trying to understand this, and this one helped me get it right away!

[@triciaparaiso9379]

I watched so many vids about getting the charge of the peptide, and this video clearly explained it!! I can now answer my homework! thank you so mucchhhh

[@justinjoseph2531]

THIS PROF IS SO GOOD!!!! My prof explained only what PI was but I had no idea how to utilize in peptides. Thank you so much!

[@RethaSetiawan]

Thank you so much! The titration scheme is a helpful method. Could we also appreciate that she's writing mirror-inverted

[@khayden777]

Actually I am writing normally. I mirror flip the image when I edit the videos prior to publishing them :). However, I have also seen people record off physical mirror as well when making these videos.

[@nidhibawane1152]

Thank you for solving my problem 😅

[@mrzed2614]

Short, simple and well explained. Great job :D

[@justinelewicki9169]

Thank you for this video! Your method really helped me understand the process!

[@khayden777]

Thank you! That is so great to hear! Good luck with your studies!

[@MingeTheAllKnowing]

gurl u just saved my life

[@noneofyabusiness1098]

thank you so much chegg just told me to only use two for a similar question without explaining why those two. but this literlitly explained why

[@khayden777]

So glad you found it helpful! Happy studies!

[@alinadunkel-wy5hk]

Gran video, mil graciasss

[@osinachiakaluka1116]

This is amazing....thanks Kate!!!!!

[@khayden777]

Thank you!

[@abhishekbehera7514]

Thank you ma'am .

[@FariaKhanSinthia]

Thank
you so much

[@heisenburger3667]

Where did the N-terminus 9.0 pKa come from? N group from Proline?

[@soumyajitchakraborty8309]

Thank you 😁

[@POKEMONMASTER23able]

Thank you so much for this ! 😭

[@TaeThei]

May I ask, what if an amino with an ionizable R group is repeated? So lets say two Lysines in a polypeptide?

[@khayden777]

Hi Tae.. since both ionizable groups will be lost at the same pH, then you lose both charges (or gain both charges) when you cross their pKa. Their charges still add to the total (i.e. both will give a +1 so two lysines will give a +2.. but when you cross their pKa you lose both so go from +2 to 0... I hope that makes sense).

[@eviekins7496]

I love you thank you

[@shashwatgaur7258]

Thank you very much!
I'm new to the subject. Can you recommend some good books to start with?

[@khayden777]

We use Foundamentals of Biochemistry by Voet Voet and Pratt in my class

[@shashwatgaur7258]

@@khayden777 I know I'm replying a tad bit later (my apologies), but thanks for the recommendation!

[@asyareedus]

what if they give us three pKas for the basic/acidic aminoacids? which ones do we use for that specific aminoacid then?

[@khayden777]

For constructing your hypothetical titration: If it is a central amino acid, then you include the pKa of the R group as it is the only free ionizable group. If it is a terminal amino acid, then you include the pKa of the free terminus (whether it is the C or N end) and the pKa of the R group.

[@asyareedus]

@@khayden777 no i mean they give us 3 pKa s for each of the amino acids (central and terminal ones) and none for the COO or N terminus .. )obviously bc they already gave us the all pKas .. im sorry im german and ive been looking for this kind of exercises in german but couldnt find any and this is the first time im seeing the question being solved right

[@khayden777]

@@asyareedus ah, so you would follow my protocol, Ideally, you would be provided the N and C terminus pKa's. They don't fluctuate too much based on the identity of the peptide, so most instructors use 10 for the N terminus and 3 for the C. However, we know they do vary slightly... but it is a safe assumption especially if the isolecetric point exists between 2 R groups.

[@asyareedus]

@@khayden777 yes thank you, i ignored the low pH pkas that were given for the N terminus aminoacid and the otherway round for the C terminus.. (bc those were the ones for groups that were involved in the peptidbinding) thank you ur video rlly saved my exam :)

[@kiban7676]

6:11 - I dont get this part ... HELP !!!!😪

[@marin9207]

Ácids And bases have ionizable groups but polar and nonpolar don’t have

[@zexicc]

Why not Ser? He has OH group...

[@khayden777]

Yes, but its pKa for the hydroxyl group is around 13. Typically much higher than biologically relevant, therefor most textbook authors put serine in the non-ionizable hydrophilic group of amino acids. That being said, there are plenty of enzyme mechanisms that rely on a coordinated effort of intermolecular interactions to deprotonate serine for covalent catalysis

[@zexicc]

@@khayden777 thanks

[@nathanbeckett7504]

This is money