Transcription
Okay, so after last week, this slide should start to make some sense to you. Um, we're looking up here at, um, some a picture of one, two, three, four, five water molecules. And, um, we can tell it says up here that water is polar. So you should know that means that it has partial charges, which means that if this is a water molecule here with an O and two H's, because of the electronegativity of the oxygen atom, this is going to be partially negative, and these H's are going to be partially positive.
And when you put a bunch of water next to each other, water molecules next to each other, they're going to weakly attract each other. This partially negative O over here is going to be partially attracted, weakly attracted to this partially positive H down underneath it over here. This partially positive H down in the bottom right is going to be weakly attracted to this partially negative O over here. So all these, um, dots are representing our hydrogen bonds that are attracting all these water molecules to each other. Not strong, not permanent, but they're there.
All right, so this, um, ability of water to have these partial charges makes it, uh, able to do lots of kind of cool, funky things. And one of the most important things for biology is that water can, lots of things can dissolve in water. Um, and basically in biology, we call water the, um, biological or universal solvent. Everything in biology is pretty much dissolved in water. Inside your body, everything's floating around in a very watery environment. Your body's full of different chemicals, but they're all dissolved in water in some way. So it's important to understand what can and what can't dissolve in water and why that is.
And basically, anything that has a charge, such as an ion like this sodium ion here or this chloride ion here, see the sodium ion has a positive charge, this chloride ion has a negative charge. Because these ions are charged, like all ions, water molecules will be attracted to them. Maybe not super strongly, but they will be a little bit. This little, this negative partial negative on this O up here is going to be weakly attracted to this, um, positive sodium ion. And these positive partially positive hydrogens are going to be weakly attracted to this chloride ion. I'm trying to draw dotted lines, but my pen is not cooperating.
All right, so those attractions, because of the, uh, char, partial charges on the water, the whole charge is on the ions. Opposite charges attract. So these particles will arrange themselves so that they can attract with each other, and that's what causes things to dissolve. If the particles that the substance is made of attracts the water molecules, the water molecules will surround it and cause it to sort of disappear into the water. Now, it's not disappearing, it's still there. It's just the particles have been separated, and they're so small that you can't see them anymore, but they're in there.
Um, so we can, we have a general term for anything that dissolves in water. We say it is hydrophilic. Hydro means to do with water, like hydroelectric or hydroplaning means to do with water. And then -philic means to like. File means to like. So this means basically to like water. So things that dissolve in water are hydrophilic, and they will generally, or pretty much always, have charges or partial charges themselves. They've got to have something on them that will cause the water molecules to be attracted to them. So something with charges or something with partial charges will be hydrophilic. Water will be able to dissolve it.
So here's, here's a quick example of some. So this, sorry, let me go back. That first example was salt. We know that salt dissolves in water, um, just for everyday life, that's an experience that we know. But now we know because salt is made up of these positively and negatively charged particles, we can understand now why salt dissolves in water because the water molecules are attracted to the charges on the salt ions.
So something a little more biological, here's a protein. So protein, this purple shape, um, over here, this is a protein molecule. Proteins are enormous, huge, some of the biggest molecules that we deal with or most complicated molecules that we deal with in biology. We're going to get into them in unit two, um, but, uh, it's, if you look at closely at this, this purple diagram here, you can see it's kind of lumpy. These lumps represent atoms that are all hooked together to build this giant molecule. This has hundreds of atoms in it. And in some of these cases, some of these atoms are going to have, if we zoom in. So down here, we're zooming in on a portion of this, um, protein molecule. And when we put this protein molecule into water, you can see that when you zoom in really closely, there is a high, there's hydrogen bonds occurring between this water molecule here and this area on the surface of the protein, like just right here, this little knobby bit sticking out.
All right, so what we know must be happening in this little area is that there must be some kind of a partial charge right here. This is going to be partially positive because it's a hydrogen on water. So this area here must be a little bit negative. And over here, we've got an oxygen, and this is partially negative, and it's being weakly attracted to this region on the surface of the protein. So this must be partially positive. How could you get partially negative and partially positive regions on the surface of a protein molecule? Well, if we look at this region right here and backtrack it over here, you see these like lumps that are sticking out on the protein? These are atoms. So maybe over here, we have an O stuck to an H. Whenever, and then they're always stuck to something else back inside here, and there's a whole bunch of bonds, and it gets really complicated. But if this is an oxygen, let me make that clearer here, if you have perhaps an O right here stuck to an H, this is going to be a little bit negative, and this H is going to be a little bit positive. It's stuck in, it's connected to other atoms back inside here. So this little knob sticking out here on the protein molecule right here is an oxygen atom that is a little bit negative, which means that if this is the knob over here, this little bit positive hydrogen will attract to it.
Now, it takes a while for all these water molecules to gradually kind of wiggle their way into the surface of the protein. Like if you see, look at the purple diagram here, uh, this, this diagram right here, you can see how kind of knobbly and kind of full of little crevices and everything this giant molecule has, like a three-dimensional surface. So for this thing to completely dissolve in water, the water molecules have got to weedle their way into all these little crevices and get attracted to all these little knobbly bits and kind of basically coat the whole protein like you see happening here. And that takes a little bit of time. It doesn't happen super quickly.
You can experience this in your everyday life if you think about maybe, uh, two, two examples. If you are going to make like a post-workout drink, one of those like protein powder shake things that you can get, or even like a meal shake, like a diet shake. If you take that powder and which is basically high protein powder, lots of protein molecules in it, and dump it into the water and drink it almost immediately, shake it up and drink it, it tastes kind of chalky and dry. You can kind of taste the powder, and it's like it hasn't really dissolved. And that's because it hasn't dissolved. The water molecules had not have not had time to wiggle their way in and amongst the molecules and attach themselves, attract themselves to the watch of the proteins correctly or completely. So it's not truly dissolved completely yet, which is why it still tastes powdery. If you mix it up before your workout, go work out for an hour, and then come back and drink it, it tastes a little better because the water has had time to completely coat the protein molecules and more more effectively dissolve them.
The other example here is in cooking. So if you were to like cook something with a lot of protein, like, like cook a roast, a piece of chicken or steak in a pan. You put it in the oven, you roast it, it comes out, you eat it, it's delicious. And then all the stuff is baked onto the pan. It's all kind of crispy and burnt around the pan. That's basically protein molecules that have kind of gotten heated up and stuck to the surface of the pan. You can put that in the sink and you can try and wash it immediately, um, and if you scrub it, you'll probably be able to get it clean. But the more, um, logical thing to do would be to fill it up with water and let it sit, right? You soak it. What you're really doing when you're soaking it is you're giving all these little water molecules here time to sneak to sneak their way into the crevices and the protein molecules and completely surround them and dissolve them. So when you come back, it wipes off much easier. It's actually a molecular explanation for why soaking your dishes and leaving your dishes in the sink for day is a good thing or a scientifically logical thing to do.
So I hope that will help you and your decision about whether you should go and clean your kitchen. I say just let it soak. Let those molecules surround a bit more. You.