00:01
All right, so let's get into this question here.
00:03
Considering the following peptide, it's quite a long peptide, what is the net charge at ph 1 and ph 14, and then if lysine is replaced with aspartic acid, what's net charge at ph 1? okay, so i started by labeling which ones were basic or positively charged amino acids, and then which ones were negative or acidic amino acids.
00:26
So i just color coded the whole thing, and then the neutral color i just chose was black, so i have one, two, three, four, five basic or normally positively charged amino acids, and three that are acidic or negative, and then the rest are neutral.
00:44
So a ph of one, that means there are a lot of hydrogen atoms and everything is going to be protonated or any group that is ionizable will be protonated.
00:56
And so going off of this, in a protein, you have a protein.
01:01
Have an in terminal and a c terminal, also called your amino terminus and your carboxylic terminus.
01:09
And all that means is here at the beginning of the protein where methanion is, there would be a nitrogen group, which would be normally in h2, and then, you know, you would draw a bunch of stuff.
01:27
And then all the way at the end where the histidine is, we would end in a carboxylic acid group should look something like this.
01:41
So these terminals will be affected depending on the charge.
01:46
So or depending on the ph.
01:49
So at ph of 1, this amino group will be protonated.
01:54
Now this only is affecting the terminals of the protein and the reason for is because there are peptide bonds being formed between the rest of these and those groups won't be ionizable, only the ends.
02:06
So the ph of 1 will have a positive charge here so we can say positive on this terminal at ph 1 and then we will have this being still positive or any of our basic amino acids they're going to stay positively charged whenever we're at a low ph okay and then we're going to have a lot of neutral charges here so serene its group won't be ionizable uh glutamic acid will stay neutral well we'll turn neutral sorry it's going to be protonated.
02:42
So instead of an o negative, it's going to be an oh group.
02:46
So neutral, neutral, protonated, protonated, protonated, protonated.
02:58
Okay, now you can simply just count these up.
03:00
One, two, three, four, five, and six.
03:04
And that is how i got this answer of having a net charge of six.
03:09
Okay.
03:10
Now at 14, this is when it changes.
03:14
So, the thionine, we go back.
03:16
Being neutral because this amino end would no longer be proponated.
03:23
So it would change back into a two.
03:27
Take that away...