Zwitterion and Amino Acid Charge Given pH and pKa

[@martinagjorgjievska1966]

oh my god, I couldn't understand this for weeks,I couldn't find any good explanatory videos and you just answered all my questions. I have my biochemistry exam on Monday. thank you

[@Leah4sciMCAT]

thank you! glad to help Good luck on Monday!

[@Josh_Morales]

Thank you so much Lea! I was struggling with this and got a 503 MCAT, now I ended up getting at 517 and will make a video about how I did it! Thank you so much!

[@Leah4sciMCAT]

That's fantastic, congratulations! And yes, make that video and help others see how they can reach their goals, too!

[@khazeemahafeez6811]

You are truly gifted when it comes to explaining MCAT content. Thank you!

[@Leah4sciMCAT]

Thank you for your kind words!

[@carolpena1075]

I can't express how greatfull I am. I've been trying to understand those concepts for weeks with my regular teacher and failed miserably. This explanation was so clear, i finally understood!! Thank you so much!!

[@Leah4sciMCAT]

I'm sorry you've had such a struggle with it, but happy that I was able to help you understand!

[@jessicahoff8574]

Just brilliant. Will be sharing with my past BioChem professor (she loves solid educational videos - knows students all have different learning styles) along with my Pre-Med base. Regret not thoroughly watching through these years ago.

[@Leah4sciMCAT]

Please do, and thanks for sharing!

[@myamitchell8675]

You are just so amazing Leah! You have assisted with turning the cogs in my brains just that little bit more every time!

[@Leah4sciMCAT]

I'm so glad to hear that I've helped it all click into place!

[@brokensymmetry1874]

It finally made sense to me while looking at Le Chatelier's principle! Thanks!!!

[@Leah4sciMCAT]

Glad the video helped! You're welcome :)

[@rampalepu9231]

Excellent job! I totally understand it now. Thank you so much.

[@Leah4sciMCAT]

+Ram Palepu You're very welcome! Glad to help

[@AR-vb4xy]

Just found this channel of yours right now! Keep up the good work Leah!!

[@Leah4sciMCAT]

Thank you so much!!

[@sowhat1444]

THANK YOU OMG THANK YOU!!! YOU SAVED ME! IM SO GRATEFUL FOR THIS CHANNEL!!!!

[@Leah4sciMCAT]

You're welcome! Happy to help!

[@mesvetnova7836]

You explain everything thoroughly! Very good videos. I've recommended this to other students

[@Leah4sciMCAT]

Thanks so much, I really appreciate that!

[@Biotechnologynerd]

I'm Really thankful to u for making this tutorial.. finally understood the concept 👍

[@Leah4sciMCAT]

Happy to help!

[@mrawesome1821]

@ time 13:15, you wrote glycine as having only one H on the Nitrogen, when it actually has 2 H's. This really confused when you started to count charges...

[@ash.toronto31]

Yeah lol

[@Leah4sciMCAT]

I’m sorry for the confusion and for the late reply. When neutral and in its de-protonated form, the free amino group of glycine should appear as -NH2. At no point does it actually exist with a single proton. I simply had it appearing that way at the beginning of the problem before I determined if the group was in its protonated (-NH3+) or deprotonated (-NH2) form.

[@daaiibrahim1652]

OMG THIS IS AWSOME , I was so confused, you broke it down so so so well!!!!

[@Leah4sciMCAT]

Thanks so much!

[@RahulGupta-uk7xy]

This concept help me to crack jee advanced 2020 question in seconds ❤❤ 👍 thanks 😊

[@Leah4sciMCAT]

YES to saving time on exam questions!

[@ryanohara4740]

You are a tremendous teacher.

[@Leah4sciMCAT]

thank you

[@n.i288]

Saved me once again ❤ thanks for doing what you do!

[@Leah4sciMCAT]

You're very welcome! Glad it helped :)

[@rustybolts8953]

Don't understand everything yet but very clear explanation and presentation. Thank You.

[@Leah4sciMCAT]

You're very welcome! I'm glad it's helping to clear things up. Go back and rewatch a few more times to help solidify the concepts.

[@lili1596xd]

thank you so much i struggled so much with this topic

[@Leah4sciMCAT]

It's a tough topic, happy to help!

[@mohammadal-shamasneh2664]

What an AWESOME explanation!! you have just lightened my road 😃thank you very much .

[@Leah4sciMCAT]

You're very welcome, so glad it helped!!

[@asiakhatoon954]

Thanks a ton, this concept was troubling me from past 2 days 😇😇😇😇thank you thank you thank you for making it crystal clear.

[@Leah4sciMCAT]

Glad it helped! You're very welcome!

[@patrickp4571]

Clear and simple as always, thank you.

[@Leah4sciMCAT]

You're very welcome!

[@brandonherron4589]

Your voice is like ASMR, It's relaxing and soothing. I like it a lot, ever think about doing deep sleep mix tapes? 🌝

[@Leah4sciMCAT]

hahaha, I haven't, but thanks!

[@ahmedelyamani6049]

you're the best, thanks a lot.

[@Leah4sciMCAT]

Awwww, you're so welcome!

[@vichuang273]

Thanks to this wonderful video! But I still don't understand that why -COOH is still -COOH after protonation and also why CH3NH3+ is still CH3NH3+ after protonation?

[@Leah4sciMCAT]

At which specific point in the video?

[@mesvetnova7836]

Because -COOH is already a protonated form of carboxyl. It can only be deprotonated now to -COO- (Negatively charged). The -COO can not accept two protons. Just as the -NH3+ can not accept a 4th proton. This is determined by the atoms' valence and number of electrons

[@sophiemay2933]

I think you may have just saved me from a meltdown. Thanks ;)

[@Leah4sciMCAT]

Glad I could help keep the meltdown away! Might I suggest booking some time just for yourself for a walk, bath, reading or something else enjoyable where you can completely unplug? Even 20 minutes can make a huge difference.

[@sarajahanara4721]

Wow you are amazing. I love it!

[@Leah4sciMCAT]

thank you

[@anashchowdhry6879]

For the last example how does HN got to H3N

[@Leah4sciMCAT]

at what time?

[@skylarmorrison5162]

Leah4sciMCAT I assume he means at 13:19 when you protonate the amino group

[@gabbyc2447]

Very clear and concise. Thank you so much!

[@Leah4sciMCAT]

You're very welcome!

[@tiggertiger9495]

this helped me on a biochem question, thank you

[@Leah4sciMCAT]

You're very welcome!

[@mohamedelnaas8466]

U just saved my life,Thank u

[@Leah4sciMCAT]

Glad I could help!

[@aderonkeolaoye8052]

Am confused, at 15:22, when you deprotonate NH2, shouldn't the charge become -1 instead of neutral?

[@Leah4sciMCAT]

NH2 is -1, but RNH2 is neutral due to having 3 bonds and 1 lone pair

[@tea5020]

This is such a good explanation thank you!

[@Leah4sciMCAT]

You're very welcome!

[@thecoreybrown]

Can someone answer this for me? I thought a molecule that has more H+ ions is BASIC and molecules that don't have that many H+ is acidic? Right or wrong?? for example which is the base and which is the acid of these 2......NaH2PH4 and NaHPO4 and why?

[@Leah4sciMCAT]

Have you seen my acid/base series? Leah4sci.com/acidbase

[@nathaniele1835]

at 12:47, would it be NH2 instead of NH? and O- instead of O? I'm just a bit confused on what the starting molecule of glycine looks like.

[@monicabarsoum3434]

I was confused about this too! idk why she didn't explain this or make a note about it at least:(

[@kousalyadevi5209]

Have the starting material as NH2 and COOH.. Remember NH2 can't be deprotonated further (to NH) and COOH can't be protonated further.

[@Leah4sciMCAT]

I’m sorry for the confusion and for the late reply. At no point does glycine actually exist with a single proton on the nitrogen or with an uncharged, de-protonated oxygen on the carboxy group. I simply had it appearing that way before I determined if either group was in its protonated or deprotonated form. There really is no “starting molecule” of glycine. It will exist at different charge states, depending on the pH of the surrounding solution. We always have to consider the pH before determining how glycine will appear.

[@catma458]

Thank you.You made it so simple

[@Leah4sciMCAT]

You're welcome

[@AnneWangJune]

Hi, thanks for the video. But why at pH13, amino group did not deprotonate?

[@Leah4sciMCAT]

You're welcome! It did deprotonate. Once it reached the pH of 13, it went from CH3NH3+ to CH3NH2. It lost a proton.

[@mannypotMD]

Really helpful. Thank you!

[@Leah4sciMCAT]

Thank you

[@marissachukwu306]

just wanted to clarify, at ph=13, the ph is greater than pka 9.6 of amino group, so amino group should be deprotonated to NH2 from NH3+ right? and thats why you get the charge on the amino group as 0?

[@Leah4sciMCAT]

At which specific part of the video are we talking about? (timestamp)

[@marissachukwu306]

@@Leah4sciMCAT at time stamp 15:50

[@Leah4sciMCAT]

@Marissa Chukwu - correct.

[@corneliusngandwe293]

Very good explaination

[@Leah4sciMCAT]

Glad you like it!

[@hmh6040]

It's so helpful! Thank you!!!

[@Leah4sciMCAT]

You're very welcome!

[@natan-elmensahsowah4581]

For pH of 13 for glycine, shouldnt the amino group be deprotonated and not protonated?

[@Leah4sciMCAT]

at which specific point in the video?

[@acepokemontrainer1]

It is already deprotonated. Instead of H3N+, it has deprotonated at pH 13 to become H2N like she has drawn.

[@dalyam2014]

Shouldn't the amine on GLY be de-porotonated at pH 13 because pH>pKa? To go from neutral NH2 to NH??

[@Leah4sciMCAT]

Yes, the amine will be de-protonated at pH 13. It goes from NH3+ to a neutral NH2. The amine group will never be written as NH (and if it was, it would be negative in charge).

[@maatherbasfar9012]

god bless you for this amazing video

[@Leah4sciMCAT]

thank you

[@kierayuan1778]

very, very helpful! Thank you so much!

[@Leah4sciMCAT]

You're welcome!

[@AquaticLogic]

This is a very good explanation, thank you.

[@Leah4sciMCAT]

You're very welcome

[@mareimart2127]

i love this! Thank you very helpful

[@Leah4sciMCAT]

You're so welcome!

[@josh6306]

This was great! Thank you!

[@Leah4sciMCAT]

You're so welcome!

[@surat8591]

Thank you!!! You are a blessing 😍

[@Leah4sciMCAT]

you're welcome!

[@stoicsingh472]

Omg you are a godsend god bless you

[@Leah4sciMCAT]

Wow, thanks!

[@curiositycatasta]

Why is the amino acid Glycine represented with an NH group instead of an NH2 group, and the COOH group as the COO group?

[@Leah4sciMCAT]

I'm sorry but I don't offer tutoring through KZbin comments. For help with questions like this and more, I highly recommend joining the MCAT Study Hall. For more details visit join.mcatstudyhall.com/ or contact me through my website leah4sci.com/contact/

[@liamckinney9717]

Would you recommend memorizing the pKa values for all amino acids?

[@Leah4sciMCAT]

Yes and no. Only memorize the estimates I discuss here: leah4sci.com/amino-acid-charge-in-zwitterions-and-isoelectric-point-mcat-tutorial/

[@JedaJess]

Thx u so much! ❤

[@Leah4sciMCAT]

you're so welcome!

[@Ruslancho99]

I love your explanation, it-s simply made and just enough :=)

[@Leah4sciMCAT]

Glad I could help!

[@manjukumar3406]

Thankyou very much mam...❤❤💖💖💖

[@Leah4sciMCAT]

You're welcome!

[@kal7708]

thanks for a great video!

[@Leah4sciMCAT]

You're very welcome!

[@gandhimanikandan2490]

at ph 13 why did the amine group get protanated ... is should be deprotonated ryt ? bcoz the surrounding has got less H+ ion they y did the NH was protonated ....im confused ..

[@Leah4sciMCAT]

+gandhi manikandan what point in the video?

[@gandhimanikandan2490]

+Leah4sciMCAT mam will the ammino acids we take in food are always in zwitter form ie amine is NH3 + and carboxyl group is coo - ??

[@gandhimanikandan2490]

+Leah4sciMCAT just nw watched ur vid again ..nw its clear just pls clarify the doubt above ...ie protein we eat has their ammino acids in zwitter form ? is it ?

[@kennedyolson9408]

Bless you. I understand this well now :)

[@Leah4sciMCAT]

Awesome!

[@neilpatel2828]

Leah, do we need to memorize the pka of the R groups for the Acid Base A Acids for the MCAT? In those the range is +2- -2 correct?

[@Leah4sciMCAT]

Yes but not 'exact' values. Remember, on the MCAT close enough is good enough.

[@atousabahrami6417]

what if you are working with basic amino acid that is already carrying +1 charge?

[@Leah4sciMCAT]

I'm sorry, but I don't offer tutoring through KZbin comments. For help with questions like this and more, I recommend joining the MCAT Study Hall. For more details visit join.mcatstudyhall.com/ or contact me through my website leah4sci.com/contact/

[@kovalchuk71]

Why do you have the Amine Group as "H2N" at the beginning of the video, but as "HN" at the end of the video?

[@Leah4sciMCAT]

Not sure I understand where you're seeing HN

[@anashchowdhry6879]

on the amino group for the last exmaple

[@acepokemontrainer1]

She drew H(space)N so that she eventually fills in all the numbers as she showed the specific pH values. Depending on the pH, the amino group is protonated or deprotonated, and she shows that with her drawings.

[@sumayauthmaan4838]

Just to clarify, does the pH look at the solution, while the pKa looks at the molecule?

[@Leah4sciMCAT]

I think you’ve got the distinction! The pH looks at the concentration of hydrogen ions in solution, while the pKa is a constant for any given molecule. The pKa gives us information about the acidity of a certain proton on the molecule and whether that proton will dissociate or not at the specified pH.

[@araza711]

You are so great! TY!

[@Leah4sciMCAT]

You are so welcome!

[@jeriessilbak7117]

Thatssss really helpfullll thanks

[@Leah4sciMCAT]

You're very welcome!

[@SuperioMan3432]

omg this makes a ton of sense

[@Leah4sciMCAT]

So glad it helped you understand!

[@LewisNoname]

I really love you, thanks !!!

[@Leah4sciMCAT]

You're welcome!

[@cerenavclar1417]

Thank you so much !

[@Leah4sciMCAT]

You're very welcome

[@chinedu7128]

LET HER COOK!!! wow, you just earned a subsciber!

[@Leah4sciMCAT]

Yay! Thanks so much for watching and subscribing! Glad you liked the video.

[@نغمة-ظ9س]

I have exams in 1hr, wish i saw this much before

[@Leah4sciMCAT]

Better late than never?

[@aramebrahimi3754]

Can't thank you enough!

[@Leah4sciMCAT]

You're very welcome!

[@Bettertobeawarriorinagardin]

So you said that the neutral form cannot exist, but that the zwitterion is the neutral form and then you claimed that it is the most common form, please elaborate I'm confused

[@Leah4sciMCAT]

I apologize for the confusion. The amine and carboxyl groups cannot both appear in their neutral form at the same time. In nature, we most commonly find amino acids as a zwitterion where the amine holds a positive charge and the carboxyl hold a negative charge. Overall, these two charges cancel out, creating a net neutral charge for the molecule. The idea is that neither group is neutral by itself, but together they form a net neutral molecule.

[@thelifeoftoolboxt4359]

Do you give tutorials about other chapters of Biochemistry?

[@Leah4sciMCAT]

For the class or MCAT? My biochem resources are specifically designed for the MCAT. For more help with MCAT biochem, I recommend joining the MCAT study hall. Full details: join.mcatstudyhall.com/

[@brijayejaye5464]

Great video

[@Leah4sciMCAT]

Glad you like it!

[@tiff67890]

bless this video

[@Leah4sciMCAT]

Thanks! Good luck to you :)

[@mianmutahir1565]

THANKU CUTIE

[@Leah4sciMCAT]

You're welcome

[@negarolfati36]

Excellent job Leah, thanks a lot! Just one question, regarding the quiz on your website: In part 3, we are asked to find the charge of Cys at PH = 4. Pka values for Cys are as follows: (Pka(COOH):1,71, Pka (NH2): 10,78, Pka(R): 8,33 ). The solution suggests change 0 for the side chain. Could you please explain this to me? I would expect to see +1 for the side chain and not zero, as PH is much less than the Pka for side chain, which means that the side chain should get protonated (conveting to S2H+ from SH). Am I missing something? All help would be appreciated.

[@Leah4sciMCAT]

You're very welcome! Since I don't offer tutoring over social media, I would first suggest you use the download link at the bottom of the practice quiz to access the PDF quiz solutions. If you would like a more detailed explanation, I recommend joining the MCAT Study Hall. For more details visit join.mcatstudyhall.com/ or contact me through my website leah4sci.com/contact/

[@tunneltrance]

thank you so much

[@Leah4sciMCAT]

You are welcome!

[@monicabarsoum3434]

i was confident until you did the example with glycine and misdrew it... it got me so confused during the entire example and now I'm just really anxious and confused :( ... please fix this....

[@Leah4sciMCAT]

at which point of the video are we referring to?

[@dearafaela3672]

why is carboxylic is charge zero when pH is 1?

[@Leah4sciMCAT]

Thanks for asking! A pH of 1 is less than the pKa of the free carboxylic acid group (~2.3) on an amino acid. Because of this, the group will appear in its protonated form as -COOH and is neutral in charge.

[@pfunzonevhusenga8602]

Brilliant

[@Leah4sciMCAT]

Thanks!

[@pfunzonevhusenga8602]

You're welcome. I nailed the test😃😃😃.

[@Leah4sciMCAT]

That's amazing! So glad to hear it :)

[@danichang2700]

THANK YOUUU!! I finally understood what to do if pKa is equal to pH! God bless you (//>^

[@Leah4sciMCAT]

You're very welcome! I'm so glad to help you understand!

[@sammser32]

I'm confused. Ka is a constant for any given acid, right? So how can it be proportional to the hydrogen concentration? Constants aren't proportional to things! Ahh!

[@Leah4sciMCAT]

Sorry you're so confused; let's get things cleared up for you. Yes, Ka is a constant for any given acid. Maybe it would be better to say that Ka is proportional to the ratio of [H+]/[HA]. It stands to reason that acids which produce a higher quantity of H+ per unit of acid would have greater Ka values (and thus be more acidic). So even though the Ka doesn’t change for a given acid, it is variable between different acids based on how much H+ that particular acid produces.

[@rufinakore]

GOD BLESS YOU

[@Leah4sciMCAT]

Thank you for that!

[@pkyoupvp]

Fantastic

[@Leah4sciMCAT]

Glad you liked it!

[@ghassanauf8103]

I don’t know but why you are so concerned about acetic acid !!! Where is the amino acid in this whole lecture!!!!

[@Leah4sciMCAT]

An amino acid is an organic compound that contains both amine and carboxylic acid functional groups. In this video, I first look at acetic acid and methylammonium, as examples of how those same functional groups would behave on their own at various pH values. Then, to apply that knowledge, I turn to the example of the amino acid glycine at 12:37 to explain how these functional groups would function together within the same molecule at various pH values.

[@michelleani_]

here from anki deck

[@Leah4sciMCAT]

Glad to have you here!

[@elmerit2848]

It's not log, it's lg.

[@Leah4sciMCAT]

In the Henderson-Hasselbalch equation, we use a logarithm with a base of 10 which is abbreviated “log”.

[@zarakristen2967]

Commonly used as log

[@آلاءزيتون-س8ر]

great explanation !! thank you ..

[@Leah4sciMCAT]

You're very welcome

[@paulmoyo8746]

Thank you so much

[@Leah4sciMCAT]

You're welcome!