all right let's continue our biochemistry playlist talking about titration of amino acids this is the fourth video on the series on amino acids if you haven't watched the previous three you will never understand anything here are your 20 proteogenic amino acids each one has a name three-letter abbreviation and a one-letter abbreviation amino acids are amphoteric they have a basic part acidic part they can accept a proton they can donate a proton who will decide the ph of the medium will decide are you in an acidic environment or in a basic environment in an acidic environment the ionizable group will gain a proton because the acid has too much proton to give all right how about in a basic solution basic solution doesn't have any protons all right so you will lose protons and give it to the solution in order to try to achieve equilibrium this is how you create order from chaos so when the ph of the medium is low ionizable groups are becoming more pronated they are gaining a proton but in a basic solution with high ph the ionizable groups are becoming depronated they are losing protons in his famous book charles dickens said they can accept protons they can donate protons he was talking about amino acids and their amphoteric properties if you remember my videos on pharmacokinetics and for macrodynamics i've sorry that a singular drug can have non-ionized portion and ionized portion at the same freaking time what determines the degree of ionization the pka of the drug and the ph of the medium in which the drug is present what if pk and ph are equal at that point you will have 50 percent of the drug as non-ionized and 50 of the drug as ionized so what is the pk it's the ph at which the non-ionized portion equals the ionized portion in other words the pk is the ph at which the protonated fraction equals the deprotonated fraction 50 50. so when the pk equals the ph the protonated equals the deprotonated hashtag equality to understand the difference between ph and pk imagine that medicosis is swimming in the water okay mitochosis is the pk the water has a ph all right the water can get colder or warmer it can get more acidic or basic but medicosis does not change same thing pk is a freaking constant for a singular molecule the ph is the ph of the medium you can add some s to the medium to make it more acidic in this case the ph will go down or you can add more bases to the medium to make it more basic in this case ph will go up but the pka is the pka medicosis is mitochosis it's a constant so there are three rules if you understand them you will answer any question correctly rule number one pk is the ph at which half is protonated and half is deprotonated and they equal each other but what if the pk is greater than the ph imagine that the amino acid exists in an acidic environment because an acidic environment will have a very low ph to the point that pk exceeds the ph all right you put me in an acidic environment i'll give you more protons yep the protonated fraction will exceed the deprotonated fraction because this is a freaking acidic medium compared to the pka conversely if the pka is lower than the ph then the protonated form is lower than the deprotonated form if you want to make it easy on you always start with the pka all right and always start with a protonated so pk protonated nice and then when this is greater than this is greater than when this is less than this is going to be less than when this is equal this is equal an amino acid has an amino group and a carboxyl group each one has a separate pka because this is peter this is paul since an amino acid has two groups that can be protonated the same amino acid will have two pkas what if the amino acid has three groups then it will have three pkas so let's say that this is carboxyl group and it has a pka one of about two how about this one has another pka of about 10. they are not the same what if you put this amino acid in a medium that has a ph of 2 well this point half of the carboxyl group will be protonated the other half will be deprotonated so let's do this first thing you write the three equations and let's go at a ph of one what's gonna happen look at the first pka about two the second pka about ten all right is the pka greater than ph here yeah 2 is greater than 1 and 10 is greater than 1. therefore both of them carboxyl and aminos will be what in the protonated they will be fully protonated what does that mean protonated means proton h therefore you will see it as cooh and not sco and you will see this as nh3 plus rather than nh2 because this has more protons and at this moment in time you have nh3 on one side and cooh on the other one okay this one has no charge this one has a positive charge therefore the entire amino acid is positive thank you so much let's change the ph now the ph is six let's talk about mr coh all right is the pk greater than the ph two is not greater than six therefore we follow rule number three when the pk is lower than ph the deprotonated will exceed the protonated oh look at this most of this is c-o-o negative d-protonated baby how about the other doofus the amino group look at it the pk is 10 is this greater or lower than the ph of 6 this is greater therefore more protonated plays i exist in the nh3 plus therefore my carboxyl exists in the co negative but my amino exists in the nh3 positive a positive wing and a negative wing that's why this entire amino acid is neutral it is dipolar it has a positive pole and a negative pole we call this a zwitter ion so the zwitter ion in german means hybrid so if you're driving a toyota prius in germany they call it zwitter ion i'm just joking but what if the ph of the solution is about 7.4 which is the normal ph in your arterial blood now pause and review it's the same answer as when the ph is six because this lies in between two and ten it's again a zwitter ion now what if the ph is freaking eleven oh eleven all right let's start with mr carboxyl right is 2 greater than or lower than 11 of course 2 is less than 11. therefore i exist in the deprotonated thank you so much how about the amino side 10 is lower than 11 oh also deprotonated so i exist in nh2 rather than nh3 look at my two wings the first wing has a negative the second wing is neutral so what's the entire amino acid the entire amino acid is negative now let's talk about the titration of the amino acid before you freak out oh my goodness shut up it's easy what does titration mean gradual change gradual change that's it look at this beautiful graph you have ph here ph of the medium is it more acidic or more basic and here is o h not h o h as you know o h is basic so as you go from here to here we are adding more bases to the solution and therefore what's gonna happen to the ph as you add more bases it's going to go up and that's why we're going upwards in this direction as you increase the bases ph is going to rise let's talk about titration of freaking glycine write the three equations down first if the ph is one oh we're here regarding the carboxyl oh one is less than 2.3 other words the pka is greater than the ph therefore what more protonated plays this will be cooh and the other one will be nh3 plus and the glycine will exist in this shape in h3 plus c08 all of them are protonated keep adding more bases more bases more bases ph is going to rise and rise and rise until you plateau why did i plateau because at this moment the ph of the solution is equal to the pka1 which is of the carboxyl group around 2.3 so you plateau translation the ph the y-axis is not changing because you are a horizontal line this is not changing when the ph is not changing we call this a buffer keep adding more bases more bases more bases until the ph is now around six okay do it for the carboxyl group and you will find that is existing in the deprotonated form however do it for the amino up still protonated and at that moment which is a ph of around six the glycine or the amino acid is existing in this form nh3 protonated co deprotonated this is a zwitter ion keep adding more bases to the solution ph is going to keep rising and rising and rising because you're making it more basic now if you do the numbers oh 13 is greater than 2.3 it's also greater than 9.6 at this moment in time both are deprotonated and glycine exists in this form deprotonated deprotonated but before we reach 13 we were at 9.6 and at this moment the pka2 equals the ph therefore what therefore i am here i am plateauing the ph is not increasing or decreasing when the ph is not changing what do you call this a buffer here is a concept for you all right as you know the amino acid had pka1 and pka2 all right can you take an average yeah an average of anything is first plus second over two let's say that we have two brothers raj and amitabh raj scored 10 on the exam amitabh scored 14 on the exam what's the average 10 plus 14 over two same thing here if the carboxyl has a pk and the amino has a pk add them together divide them by two that's the average what do you call this average of course professors gotta make everything more difficult they call it the pi what the flip is that it is the point of iso electricity what in the world is that it's the ph at which the molecule is electrically neutral look at these three forms here is a form here is a form here is a form which one is electrical neutral oh this one because i have a positive wing a negative wing this is the zwitter ion look at this look at this what is the ph of this you go down and you intersect with here oh look at here 5.95 this is your p i how did you get the 5.95 easy what was the pka here 2.3 and the pka here 9.6 add them divide by two 5.95 it is the ph at which the amino acid is freaking neutral next let's talk about the concept of the slope what's the slope a slope is the change in the vertical axis over the change in the horizontal axis in this case it's delta y over delta x also the slope equals tan theta what's theta theta is the angle between the x-axis and the y-axis this angle right here let me ask you a question line a line b and line c which one has the greatest slope oh whoever has the greatest angle of course c look at this angle has the bigger angle it's bigger than b and it's bigger than a so c has the bigger slope in other words the bigger the angle the bigger the slope c by the way is more vertical than b and b is more vertical than a so we can say that the more vertical the line the greater its slope the more steep the line the greater its slope conversely the more horizontal the line the lower the slope so look here you have a green line and a purple line which one has a higher slope of course the more vertical this is a higher slope than this and what's the slope the change in the y-axis over the change on the x-axis it's the change in ph so you see here at that moment i have the high slope and i have the highest change in ph look at ph is going from here to here that's a huge change we went from like three to nine or whatever at this interval you have the high slope and the greatest sensitivity to changes in ph on the other hand look at this oh it's horizontal it has the lowest slope therefore minimal to no change the ph is not budging an inch to the ph when the ph is not changing we call this what buffer this is a buffer this is a buffer because they are horizontal but this is not a buffer glycine versus glutamic acid glycine is easy remember stage one stage two stage three in the beginning here was positive wing here was no charges so the net result is positive let's call it positive one because this is positive and this is nothing so it's a positive and this is just one positive let's look here positive wing negative wing what's the net what's the total it's neutral zero zwitter ion later it became negative this is negative and this is nothing so negative one from here to here this was deprotonation another deprotonation you go from here to here let's do it for glutamic acid but glutamic acid is unique look at it and respect it it has cooh and co oh two of them yes indeed so in the beginning positive one because this is just one part deprotonated ones look at that co negative and that's his weaker ion deprotonated again you have two negatives and one positive which gives you a negative one you can do it again so you have negative negative and nothing and this will be negative two mind you peter and paul are not the same that's why each one has its own unique pka same thing here we have peter we have paul and we have raj h1 has a different pk let's look at glycine here is glycine how do you get the pi is 9.6 plus 2.3 over 2 you get 5.95 let's do it for freaking glutamic acid you have 9.6 2.3 and 4.2 which two numbers should you use well think about it the addition of an extra carboxyl group has rigged the system we only use the carboxyls oh because these are two and this is only one so shut up we'll talk about these two point three plus 4.2 over 2 we get 3.25 the pi of glycine was 5.95 but the pi of this freaking glutamic acid is 3.25 translation glutamic acid becomes neutral at a lower ph compared to glycine because the pi is the ph at which the molecule is electrical neutral since the pi of glutamic acid is lower than the pi of the glycine therefore glutamic acid will become neutral at a lower ph compared to glycine lysine remember i promised you a great story about lysine so lysine is a totally different system now this doofus has two aminos so it has raked the game so forget about the carboxyl we'll add the amino to the r so 9.6 plus 9.9 over 2 you get 9.75 of course this is higher than glycine it's also higher than the pi of the glutamic acid therefore lysine becomes neutral at a higher ph compared to glycine it's also higher than that of glutamic acid so if you want to put them all together here's the pi if you're talking about a neutral amino acid you count the amino and the carboxyl but here if it's acidic you count the r and the carboxyl get above the amino if it's basic forget about the carboxyl and here is the best slide in the entire video how do i determine the amino acid type look at the pi only all right the pi is six that's probably a neutral amino acid such as glycine because the pi of glycine was about 5.95 that's about six if the pi is less than six oh that's an acidic i mean that's amino acid it's an excited chain such as glutamic acid how do i remember it i remember it because the peak i is the ph at which right so think about it as the ph of course when the ph is low we say acidic when the ph is high we say basic same thing here when the pi is low we say acidic when the pi is high we say basic the only difference is the neutral ph is about seven but the neutral pi is about six some pearls for the pros what's the difference between amino and amine or amino okay amino is c bound to n with a single bond but look at the amino double bond don't forget the ph and the pka they are also involved in something else called the henderson hasselbalch equation what if the numerator equaled the denominator now when this equals this the ratio is going to be 1 what's the log 1 0 baby and now the ph equals the pk of course as you add more bicarbonate ph goes up and as you add more carbon dioxide ph goes down if you want to learn more about the ph check out my acid-base imbalance course on my website medicosisperfectstellis.com thank you for watching please subscribe hit the bell and click on the join button you can support me here or here go to my website to download my premium courses thank you for watching as always be safe stay happy study hard this is mithicosis perfectionist where medicine makes perfect sense