 Welcome back everybody, just two more videos to go until we're done with video lectures for the course. Now for the past couple of videos, I've been talking about the fact that different proteins fold up in their own special ways. I want you to think of protein molecules as like primadanas. If you don't know what a primadana is, it's like a very sensitive high class person. It's like the pain in the ass actor or actress on the set who says, I can't work under these conditions. The water in my trailer is not Evian and I need the brown M&Ms taken out of the candy jar because I don't like brown M&Ms and I don't like to see them. They're very sensitive people. Protein molecules are very sensitive molecules as well. What do I mean by that? What I mean by that is protein molecules need very specific temperatures to fold up properly. If you don't have the right temperature for a protein molecule to fold up, it will unfold or it will never fold to begin with. It will fall apart. They need the correct pH. They need very specific pHs to work properly. They need the right salt concentrations and many other things. They need the conditions to be just right for them to fold up properly and do their jobs. Otherwise they start complaining about the M&Ms. So if the conditions are not correct, proteins will unfold in 3D and they won't do their jobs, which can be a big problem for the cell. There's a special name for when proteins unfold. It's called denaturation and the verb is denature. So if a protein unfolds, you say the protein denatured. All this means is moves away from its natural state. So naturation just means natural. D means away from. Please don't say denaturize or denaturization because it sounds like fingers on the chalkboard to me. Here is an example of protein denaturation. So if you have ever made sunny side up eggs, when you crack the egg onto the skillet, this part here is not white at the beginning. It's clear. That liquid at the beginning that ends up turning white, but it's clear at the beginning, it's basically water with a bunch of folded up protein molecules dissolved in it. Those protein molecules are all folded up and they're nice and happy, but you put them on the skillet and the skillet gets hot and the protein molecules that are properly folded up and dissolved there, they don't like the hot temperature. They're not accustomed to it. The chicken certainly is not accustomed to living at the very high temperatures. So those protein molecules that were happily dissolved and happily folded up, they start to unfold. They unfold and they kind of stretch out like this. And all those hydrophobic amino acids that used to be buried on the interior of the protein molecule are now exposed to the water. Nobody's happy. So what ends up happening is those stretched out protein molecules start to slam into each other to try to bury their hydrophobic amino acids away from the water. And there's so many of them that slam in together to each other that they undissolve from the liquid and they end up turning that clear liquid into a white liquid or into a white kind of gel actually. And so what you're looking at there is denatured chicken proteins. So there you go. Next time you eat sunny side up eggs you can get, you can be a nerd too. Now we're going to take a detour away from denatured proteins and proteins folding and unfolding for a moment and we're going to come back to it though. On this slide I want to talk about something called an enzyme. I mentioned this very briefly in one of the earlier videos. I want you to know this definition. Enzymes are biological molecules that speed up chemical reactions. If you remember from much earlier in this course somewhere in chapter seven I believe, we say that anything that speeds up a chemical reaction is called a catalyst. So enzymes are just a special form of a catalyst. Enzymes are catalysts that are made of biological stuff. One of the things I want you to know is that enzymes speed up chemical reactions. Enzymes are usually protein molecules. They don't have to be protein molecules. They can be other types of biological molecules but usually people think of enzymes as protein molecules and that's what I want you to do too. They also have to fold up in 3D to do their job. If they don't fold up in a certain way in three dimensions they won't be able to speed up whatever chemical reaction they normally speed up. Now this gray blob here is supposed to be some pretend enzyme and you can see that you can see that it has a certain three dimensional shape and so they're keeping this very simple but the general idea is true. Let's pretend that this enzyme speeds up the conversion of whatever this molecule is into maybe it splits that molecule into two smaller molecules and these two molecules go off and do something important in the cell. So this enzyme is important for converting whatever this molecule is into these two little molecules that are also important. There are a couple of things that I want you to know. There are some words that I want you to know here. Usually when I talk about a chemical reaction let's say molecule A turns into molecule B, the stuff on the left I call the reactant, stuff on the right I call product. Well in this particular reaction here is the stuff on the right and well they call it products right there it is. Here's the stuff on the left side of the reaction they don't call it reactant they call it substrate. So there's the first word I want you to know. Substrate just means a reactant that sticks to an enzyme that's all it means. Substrate is a fancy word for reactant that sticks to an enzyme. Another thing that you should notice is the shape of this enzyme matches the shape of the substrate. You can see there's this little spot carved out here where the substrate or the reactant can sit down in and this is an important part of the enzyme molecule. The part that has the matching shape the part of the enzyme that has the matching shape has its own special name it's called the active site. So I want you to know that as well. The active site is the part of the enzyme molecule that has a shape that matches the shape of the substrate. And we're going to talk about active site in the next video which I believe is also the last one so you should keep this in mind but we're going to go back to protein folding map. So here is a graph on the x-axis of this graph they're plotting temperature in degrees Celsius. On the y-axis of this graph they're plotting something called reaction rate. What they're really doing is they're taking one specific enzyme and they are measuring how well the enzyme works to speed up a reaction at different temperatures. How well does the enzyme work to speed up their action at 10 degrees Celsius? How well does the reaction work to speed up their action at 20, 30, 40, 50, 60 degrees Celsius? And they plot how well the enzyme works at different temperatures on this chart. If you're up high on the chart then the enzyme is working really well to speed up their action. If you're down low the reaction is not working so well. So the question I have and you can pause the video and think about these is does whatever this react whatever this enzyme is is it working well at 10 degrees Celsius? On pausing the video the answer is no. It's not working well because we're making a mark really down low on the y-axis so the enzyme is not working well at 10. Is it working well at 20 degrees Celsius? Works better than what it then it was working at 10. It's up higher but I wouldn't say that it's working well. The question I want to ask now is what temperature over here does the enzyme actually work best at? You can pause the video and think about that. Now on pausing the video well here the temperature that the enzyme works best at is in the high 30s in degrees Celsius. I would guess that it's about 37 degrees Celsius. The temperature that the enzyme works best at has a special name. It's called the temperature optimum or the optimum temperature. That's just fancy talk for what temperature does the enzyme work best at. And what's happening is if you go too far above the optimum temperature, if you go too far above 37 degrees Celsius, the enzyme starts to unfold. It starts to denature. It doesn't do its job, right? You can weigh down here if you go to 50 degrees Celsius. Basically the same thing is happening if you go in the opposite direction. If the enzyme gets too cold the enzyme also stops working. So I want you to know what optimum temperature or temperature optimum means and oh they spell it out right here. They say denaturation. Another thing that I want to point out is well is there anything special about 37 degrees Celsius? Those of you who are pretty familiar with the metric system you know that this is this is normal human body temperature. So if you had to guess where this enzyme came from a reasonable guess that it is an enzyme that comes from humans or some other animal that is similar to humans and has a similar body temperature to humans because usually the enzymes are going to work best at whatever temperature the organism that they're part of is normally accustomed to. So since we have a body temperature of 37 degrees Celsius most of our enzymes probably have an optimum temperature of somewhere around 37 degrees Celsius. So the larger point that I'm trying to make here is that sometimes you can learn about something about the enzyme just by looking at its optimum temperature. We can look at this and say optimum temperature is 37 degrees Celsius maybe it comes from humans. This picture is also supposed to illustrate that point but in a different way. This is a picture of a lake at Yellowstone National Park. If you look at this white stuff this is basically steam coming off of the lake because Yellowstone National Park is built on a giant volcano and a lot of the earth underneath Yellowstone is extremely hot and a lot of the lakes are extremely dangerous. The water in here is really really hot and you do not want to go for a dip in that water because you're going to end up dead but I'm not here to talk about the water. If you look there's like a yellow stripe next to the lake and then there's an orange stripe next to that. Those stripes are actually bacteria and those are really weird bacteria they have evolved to grow at temperatures that are almost boiling for water. So we our body temperature is about 37 degrees Celsius. The body temperature if you want to think of the bacteria is having bodies they're living at about 90 degrees Celsius which would kill us very quickly. That's where they are accustomed to working and if you look at the enzymes in those bacteria their optimum temperature is usually somewhere around 90 degrees Celsius and if you try to get those enzymes to work at our optimum temperature at 37 the enzymes fall apart they don't work. So that's another example of temperature optimum. This is something related to temperature optimum but instead of messing with the temperature on the x-axis they are messing with the pH. Again they have one specific enzyme its job is to speed up a chemical reaction. They change the pH that the enzyme is working at and they measure how well the enzyme speeds up their reaction. If the enzyme speeds it up really well you make a mark up high and it doesn't speed up their reaction very well and make a mark down low. They say how well does the enzyme work at different pH values? Well pH 5 does your enzyme work very well? No it's down low. Does it work well at pH 6? It works better but I wouldn't say it works well. You can say well what pH does this enzyme work best at? You can pause the video and think about that. If you look whatever the enzyme is the best pH that it works best at is in the low sevens let's say about 7.3 and if you go too far in either direction the enzyme unfolds it denatures and it stops working. So whatever this enzyme is it's accustomed to being in an environment where the pH is in the low sevens. So if you had to guess those of you who know a little bit of biology this stuff this enzyme might be part of human blood because the human blood pH is very tightly controlled to be around pH 7.3. I forget the exact range though. So again you can learn a little bit about enzymes that you might not have expected to learn just by looking at what pH the enzyme works best at and the pH that the enzyme works best at I guess what it's called. It's called optimum pH or pH optimum so I want you to know that as well and that is the end of this video. There's one more video to go.