Isoelectric Point - Video Tutorials & Practice Problems
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concept
Isoelectric Point of Amino Acids
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in this video, we're going to begin our discussion on the ISO electric point of amino acids. So the is electric point can actually be abbreviated with letters P I, which is shown here in parentheses and really the is electric point is really just a pH value. It's really just a specific or an exact pH at which a molecule is going to have no net charge and if it has no net charge. What that means is that if there are any positive charges that they're gonna be completely balanced by negative charges, because the overall net charge of the protein is going, or of the amino acid is going to be zero when the P H is equal to the isil electric point. And so, in our practice videos for this topic, we're going to be asked to calculate Theis Electric point of amino acids. And so it's really important to keep in mind that the is electric point is always just gonna be the midpoint or the average between just two PK a values. And so that's important to keep in mind because even if there are three p k A values given to you or four or five or however many they give it give you the ISO electric point is always just gonna be an average of just two p. K s. And so that's really, really important to keep in mind and specifically the way that you know which to PK esto average is gonna have to do with the fact that you're gonna wanna average the to P. K s for the two ionization that involved the neutral species. And so that might sound like a little bit of gibberish to you guys. But really, all I wanted you guys to know is that when you're calculating the P I in our practice videos later on, you really just want to make sure that you're gonna Onley average two p. K s. And so that's really all I want you guys to know for now. Now, another important trying to keep in mind is that mawr acidic amino acids so the more acidic amino acids actually have mawr acidic p I values a more acidic is electric points and the same applies with basic. So the more basic amino acids have more basic P I value so that's an important trying to keep in mind. And then the last thing I wanna leave you guys off with is that when the P H is equal to the P I of a molecule, we already know that the molecules gonna have no net charge like we already stated earlier. But what's also important to know is that the molecule, when it has no net charge, it's actually not going to migrate in an electric field. And that's really why the is Electric point is such a valuable property because scientists can adjust the pH to try to get it to equal the exact p I of a molecule. And that means that it's gonna have known that charge and they can use the is electric point of a molecule in a technique called electro for recess and electrophoresis basically allows scientists thio separate proteins that have a net charge using an electric field. And we'll talk a lot more about electrophoresis and another topic later on in our course in a different video. But for now, all I want you to know is that the P I or the ISO electric point of a protein or amino acid is a useful property because it allows them to separate and isolate specific amino acids and proteins of interest using electrophoresis. And so, in our next video, we're going to talk about how do you go about calculating Theis Electric Point, often amino acid with a non ionized able our group. So I'll see you guys in that video.
2
concept
Isoelectric Point of Amino Acids
Video duration:
2m
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So in our last video, we said that the ISO electric point or the P I is just a ph value. It's the exact pH where molecule is gonna have an overall neutral charge. And so now that we know that we can talk about how to calculate the ISO electric point of amino acids with non ionizing our groups and so the is electric point can actually be pretty easily calculated just by using the P k A values of a molecule. And the amino acid is electric Point is really just a simple average. It's really just a pretty simple average of the appropriate to PK a values. And that's what we said in our previous video, too that even if you're given multiple PK a values that the P I is always just gonna be an average of two p. K s. And so the good thing is that with non ionizing Balart groups, um, these amino acids on li have to PK is so it makes it pretty easy to figure out which to PK is you need to average and so down here what we have is the formula for the is electric point and What you could see is that the is electric point is really just the average of the correct up PK A values the proper too. So we have PK one and P k two and it's just gonna be an average of these two. And so, in our example, it asked us to calculate the ISO electric point of veiling and recall that veiling is one of the 13 amino acids that does not have an ionized able. Our group veiling has a non ionizing Volare group, which means it only has two PK a values and the two PK a values air given to us. So all we need to do to calculate the ISO electric point is to take the average of the two. So, Theis Electric Point, it's just gonna be 9.62 plus 2. divided by two. And so this comes out to 11.94 divided by two. And if we type this into our handy dandy calculators, theano sir comes out to be 5.97 And so what we can see is that the p I availing is going to be 5.97 which matches up with Option C and all the other options are incorrect. So we could give See a check mark here to indicate that C is correct. And so we'll be able to get more practice Calculating the ISO electric point of non ionized able are groups of amino acids with non invisible are groups in our next practice videos, so I'll see you guys in those videos.
3
Problem
Problem
Draw the structure of Leu and determine its pI. pK a1 = 9.6. pKa2 = 2.4.
a. 7.59
b. 6.0
c. 3.91
d. 5.5
A
7.59
B
6.0
C
3.91
D
5.5
4
Problem
Problem
At any pH below the pI, the population of amino acids in solution with non-ionizable R-groups will have:
A
a net negative charge.
B
a net positive charge.
C
no charged groups.
D
no net charge.
E
positive and negative charges in equal concentrations.