Amino Acids and Henderson-Hasselbalch - Video Tutorials & Practice Problems

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Amino Acids and the Henderson-Hasselbalch Equation

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in this video, we're gonna talk about amino acids in the Henderson hostile back equation. So recall that way. Back in our previous lesson videos, we reviewed the Henderson Hasselbach equation from your old chemistry courses. And really, this lesson here on amino acids and Henderson Hustle back is just a necks tension of those older lesson videos and a lot of the principles and concepts that we already covered are just gonna be reviewed and applied directly to amino acids. But if you don't remember much about the Henderson hostile back equation, make sure you go back and re watch those older lesson videos before you continue here. Now. That being said, recall that the Henderson Hasselbeck equation expresses the relationship between the solution pH and the P K A of the Ionized Herbal Group. And typically, the Henderson Hasselbeck equation is used to determine one of two different things. The first is the final pH of a weak acid solution after it reaches equilibrium, and the second is the ratio of the concentration of conjugate based to the concentration of conjugate acid. When we're already provided with the pH. Now moving forward with the practice problems in this topic. It's important to know that the Henderson Hasselbeck equation is applied independently to each of the ionized herbal groups of an amino acid. And the concentration of conjugate base to concentration of conjugate acid ratio can actually be used to calculate the average net charges of ionized able groups. And so down below. What we have is the Henderson Hasselbach equation, which we know is the pH of the solution, which equals to the P K, a oven ionized herbal group, plus the log of the final concentration of kinda get based over the final concentration of conjugate acid. And so moving forward, we're going to cover an example of how to apply the Henderson hostile back specifically to amino acids. And then you guys will be able to get a lot of practice with that. So I'll see you guys in those videos

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example

Amino Acids and Henderson-Hasselbalch

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All right. So here we have an example problem that wants us to calculate the percentage of protein ated Amino group or NH three plus in the our group of Listen specifically at a ph of 9.8. And then it tells us that the PK of license our group or licensed PKR is equal to 10.8. And so notice over here I've drawn the structure of listen just for visualization purposes and notice that we're on Lee being asked about one of license ionized able groups, and that is the amino group in the our group of lysine. And so notice that the very end of license our group there is an amino group. And really, this question is just asking us what percentage of all of the license and solution would have a protein ated amino group in its our group at a ph of 9.8. And so we can use the Henderson Hasselbach equation to help us determine that answer and so notice that were given the pH of the solution as 9.8 and were also given the relevant PK A for the Invisible Group, which is 10.8 And so really, the only thing that we're not given as this ratio of the final concentration of conjugal based over the final concentration of kanji acid. And so we'll need to solve for this ratio here in order to calculate the percentage of the pro nated amino group and so again, notice that were given the PH year of 9.8 so we could go ahead and plug that in down below 9.8. And that is gonna be equal to our PK a, which is again given to us as 10.8 over here so I can plug that in down below, plus the log of the concentration of conjugate base, which I'll abbreviate with CB over the concentration of conjugate acid, which I'll abbreviate with C A. And again we're looking to solve for this yellow ratio right here. So what we'll need to do is start toe isolate for it so we can subtract 10.8 from both sides of the equation. And of course, 9.8 minus 10.8 is going to be negative one. And so this is going to be equal to the log of the concentration of conjugate base over the concentration of conjugate acid. And again, we're trying to isolate for this ratio here. So we want to get rid of this log. And the way that we get rid of the log is to take the anti log. And so if we take the analog of one side of the equation, we have to take the analog of the other side of the equation. And the analog of a number is literally just going to be 10 raised to the power of the same exact number. And so this is going to be equal to remember. The log is, uh, removed through the anti log, and so we're just gonna have the concentration of conjugate base over the concentration of conjugal as it and so 10 race to the negative one is essentially the same thing as 1/10. So this is the ratio that we were trying to solve for and really, what this ratio means is that for every one conjugate base, so one contract basis at the top for everyone conjugate base, there are going to be 10 conjugate acids. And so, essentially, what this means is that with this ratio that we have here, uh, that there's going to be a total of 10 of 11 molecules so total of 11. And that's because 10 plus one is 11. And so, essentially, because we're being asked about the protein ated amino group, we need to realize that this is really the conjugate acid form because it is a protein ate, it has an extra hydrogen. And so this is the conjugate acid form. And because it's asking us about the percentage, all we need to do is take the ratio of the conjugate acid to the total. And so we have 10 conjugal acids, and for every 10 kinds of assets, we have 11 total molecules, and so this is gonna give us a ratio. But we want a percentage, so we just multiply this ratio by 100%. And of course, this is gonna come out to about 90.909% if you type that in your calculator, which is about equal to 91%. And so essentially this percentage here is the percentage of amino group in our group in the our group of slicing that will be pro nated at Ph. 9.8. And so that matches with answer Option B so we could go ahead and indicate that be here is the correct choice. And so that concludes this example problem and you guys will be able to get a lot more practice utilizing the Henderson Prospect equation with amino acids in our next couple of practice videos, so I'll see you guys there.

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Problem

Problem

At pH 11.8, what is the % of protonated amino group in the R-group of Lysine. (Lysine's pK_{R} = 10.8)?

A

9%

B

45%

C

3%

D

86%

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Problem

Problem

Draw Glu & calculate the % of -COOH in the R-group of Glu at pH 3.2. (Glu pK _{R} = 4.1).

A

88.8%

B

58.1%

C

97.3%

D

21.6%

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Problem

Problem

Draw Asp & calculate the pH at which two thirds (2/3) of Asp's R-group is dissociated. (Asp pK_{R} = 3.9).

A

4.2

B

3.5

C

7.4

D

8.9

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Problem

Problem

Draw Arg & calculate the pH at which 23% of Arg's R-group is dissociated. (Arg pK _{R} = 12.5).

A

11.98

B

9.93

C

8.41

D

12.67

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Problem

Problem

What is the ratio of [conjugate base] to [conjugate acid] for each of Histidine's three ionizable groups at pH 7?

A) Amino group ratio: ________________

B) Carboxyl group ratio: ________________

C) R-group ratio: ________________

D) Use the ratios above to determine the average net charge of the ionizable groups & the entire His molecule.

1. Net charge of Amino groups: ____________

2. Net charge of Carboxyl groups: ____________

3. Net charge of R-groups: ____________

4. Net charge of His: ____________ (Hint: sum previous 3 charges).