 Welcome back everybody, I think this is going to be a short video. This is mostly just to describe a little bit of some tricks or potentially confusing things about looking at drawings of amino acid molecules. So on one of the very first slides covering chapter 16, I showed you this and I said this is a generic amino acid molecule, I said the amino acid molecules will always have an amine functional group, they will always have a carboxylic acid functional group, they will always have a carbon in the middle, that carbon in the middle will always have a hydrogen stuck onto it and then some other stuff will be stuck onto that carbon in the middle as well and this other stuff makes the amino acid molecules different from each other. The problem with this drawing is that sometimes students can think oh okay, every time I see an amino acid, the carboxylic acid part will be pointing to the east, it will be pointing that way or to the right I guess, the amine functional group will always be pointing to the left, the hydrogen that's stuck on the carbon in the middle will always be pointing up and the side chain will always be pointing down. It doesn't have to be that way and it won't be that way on a quiz or a test. I can rotate this thing any way I want and you should still be able to figure out where everything is, right here the carboxylic acid is kind of pointing to the northeast, the amine functional group is pointing to the southeast, the R group is pointing in a weird way but this is still an amino acid and you should be able to recognize it even if it's twisted and bent, I can twist and bend it in many different ways. Another thing is that this is especially true in biology textbooks, a lot of times instead of drawing this, this is called a carboxylic acid functional group, people will draw a carboxylic acid like this, now this doesn't look anything like that, it has the one carbon, two oxygens, and a hydrogen but it doesn't show you the double bond and it doesn't show you who is connected to whom but this has done a lot of the time. So the reason that I'm pointing this out is because sometimes it's just shown to you and I want to emphasize something, if you ever see the atoms written in this pattern this is chemistry shorthand for carboxylic acid. It's just easier to write than all of this so people write it like this. The real reason it's written like this is a financial reason and that is back 100 years or so ago when scientists wanted to publish something and they wanted to show a molecule like this, the printers charged a lot of money to put this kind of thing in print because this is complicated, the printers did not charge so much money if you just wrote all of the letters like this. So the people who are doing this kind of stuff, one of the things they said is look we want to save money as long as we write it this way, as long as everybody is on board this is always going to mean that the atoms are connected like this and then we can save a little bit of money and as long as everybody is clued in you know that this means carboxylic acid and it's kind of stuck. There is another chemistry teacher who sometimes teaches at Goodwin who absolutely despises this but it gets used a lot so I'm just telling you. Another thing much earlier in the course I showed you a formula like this and I said oh this is the formula for acetic acid. In the beginning of the course I said how many carbons are there, oh there are two, how many oxygens there are two, how many hydrogens there are four and this was a cautionary tale. This was me telling you hey you have to look at the whole molecule because sometimes the atoms will be spread out like they are here and I said well why bother spreading them out? Why do I have to write it like this? Hopefully now that you will see that when you write COOH here this is telling chemists who have been trained that the C, the O, the O and the H are connected to each other in a carboxylic acid. You could write CH4O2 that's the same formula as this thing here but this doesn't tell you that there is a carboxylic acid in there somewhere. Anyway that's a long winded way of showing you different ways that the amino acid molecules can be presented. There is one more thing on the next slide. In most liquids, in most water based liquids including your cells and other body fluids, the carboxylic acid of the amino acid and the amine functional group of the amino acid are actually charged. What do I mean by that? This is the amino acid molecule the way that I have been drawing it, in other words it looks like this but if you put this molecule into water most of these molecules will not look like this. The reason is this is an acid and if you remember our definition of acids is acids are able to donate H+. If you put this into water this H will get donated it will fly away, it will move away and what will end up happening is this oxygen because this H plus got released this oxygen will have a negative charge. So if you put an amino acid molecule like this into water most of the time that H leaves and so that little part of the molecule has a negative charge. The other thing is that this part of the molecule can act like a base and if you remember what bases do they can accept H+. So if you put this kind of molecule into water a lot of times this part will pick up an H+. It will end up with a third hydrogen, it will end up with a plus charge. The point I am trying to make is that sometimes when people draw amino acid molecules and textbooks they draw them like this. If you look there is no electrical charge written on any single atom here but this is not really the most realistic way that the molecules exist in your body, in your cells. Usually this H flies off and usually this part of the molecule picks up another H+. So other times when people are trying to be more accurate in the way they draw amino acid molecules they will say hey actually this nitrogen here has a third hydrogen stuck on to it and has a positive electrical charge. This oxygen here used to have a hydrogen stuck on to it but that left and it has a negative electrical charge and most of the amino acid molecules in your body are like this. But sometimes they are drawn like this which is how I drew it at the beginning. Sometimes they are drawn like this which is slightly more realistic. You don't need to know this word, that is a German word that has to do with the electrical charges here but don't worry about it. If you were paying close attention and you might not have been paying close attention, if you are paying close attention when I showed you the 20 universal amino acid molecules you will notice that they were drawn with the electrical charges. They had the hydrogen leave there and give you a negative charge. They had the third hydrogen stick on to this nitrogen here and you can see the positive electrical charge. Your book is trying to draw the amino acids in the more realistic way. So you should be aware that sometimes it will be drawn like this and sometimes it will be drawn with the charges. I think that is the end of this video.