Hi in this video we're gonna be talking about important chemical bonds and attractions. So before we can talk about chemical bonds, we really need to understand the property of atoms. Now, I know that you've already gone over this and some of your intro chemistry classes. But I'm going to take a minute to just review these concepts and try to connect them to cell biology so that we understand why they're going to be important moving forward. So the first thing is that the properties and structure of atoms allow for the formation of chemical bonds. Now we know this atoms form chemical bonds and that's important. But how they form chemical bonds and what type of bonds form in cells is particularly important for this class. So first is that atoms have a core of neutrons and protons, which is surrounded by this negatively charged electron cloud. Um And so this electron cloud is made up of electron shells which contained the orbiting electrons. So if we look down here at this image, you can see um here's the core of this carbon atom and that's where the protons and neutrons are. And then surrounding here are these electrons and they are in these shells. Um and they orbit this, the atoms core. Now the formation of chemical bonds happens because each of these electron shells want a certain number of electrons. And when they don't have that number, they're less stable and they want that number. So they seek out that number by forming other by forming bonds with other atoms. And so in this case we have two carbon atoms here forming a bond um actually sharing those electrons. Now, for cell biology now in chemistry there's a ton of um atoms that we can deal with and form bonds with and deal with. But in cell biology we really limit this. So in cells the ones we most commonly deal with, our carbon, hydrogen, nitrogen and oxygen, which make up 95% of the chemical bonds and sells. Now another unique thing is in chemistry we deal a lot with actually saying, okay, well this individual atoms by itself, how does it interact with other individual atoms? But in cells that doesn't really happen, we don't have the single carbon atom that's like floating around doing something and the same with oxygen, but instead they form these complex structures that then go on to have particular functions. And so we're, when we're talking about cell biology, we're gonna be talking about the important bonds that helped form these complex structures. And so um for carbon for instance, which is a hugely important atom in cell biology, it can form four bonds um and really serves as this foundational element of biological chemistry. So carbon is going to be really important, moving forward. So now let's move on

Okay so there are atoms themselves and they form bonds. So now let's talk about some of the bonds that they form. Um One of the really important bonds atoms form themselves is called a covalin bond and this is formed the sharing of electrons. So this occurs when the outer electron shells of two molecules want to be complete. So in order to do that in order to make themselves complete, they share electrons. Now they can share two electrons and that forms a single Covalin bond. They can share four electrons that form a double Covalin bond and they can share six electrons which is referred to as a triple bond. You may remember some of this from your intro chemistry class Now molecular molecule polarity which remember is due to the unequal sharing of electrons. So molecules that are polar unequally share electrons and molecules that are non polar share electrons equally. So um polarity results in sort of a concentration of these negative or positive charges on different atoms in a molecule. Um and so if we just scroll down here for one second I'm gonna scroll back up. But if we look at this Covalin bond of a water molecule you can see that they're sharing electrons here. But in the process of sharing the electrons the oxygen atom actually um sort of unequally takes all of those electrons doesn't share them as equally. So it ends up with this negative charge. Whereas these hydrogen atoms down here are still sharing the electrons but they actually end up positive and this results in um a polar water molecule. So now Um so polarity. So there is a term that we use and it's called electro negativity and this describes atoms with the ability to attract electrons. So in the case of the water molecule, the oxygen atom is electro negative because it can attract those electrons stronger than the hydrogen that its bond to. Now. Covalin bonds are really strong. And so they have a high bond strength which is defined as the amount of energy needed to break the bond. Which makes sense because if it's if it's a strong bond then how you measure it through bond strength is going to have to measure how much energy is needed to break it. Um So more energy to break it, it means it's a stronger bond. Um and so you don't need to know this number, but I just sort of as a um comparison moving forward and talking about some other bonds. Um The bond strength required to break a single carbon oxygen bond, which is koel UNt is going to be 84 kilocalories per mole. So that's just a bond strength. That's how it's measured in chemistry. You may see this as killer joules per mole. Um Instead of kilocalories, but in cell biology we really do focus on the calories instead of the jewels. Um So now we talked about co violent bonds. So let's move on to some other type of bonds

Okay, so now let's talk about non violent bonds. So non violent bonds can also be called inter molecular forces. And they are bonds that do not this is important do not involve the sharing of electrons. So one type right here that we're gonna talk about is ionic bonds which can be referred to assault bridges. And they are formed by donating or accepting electrons giving or taking away electrons not sharing. So this occurs when the outer shell of electrons donator take in electrons in order to be complete. So let's look at this image while we talk about how this happened. So this is looking at sodium chloride or table salt, salt. Um And you can see that the sodium has an extra electron. Um That is making it shell um sort of have too many electrons. And the chloride actually as only seven um and is missing an electron. And so it wants both of these molecules want or both of these atoms want their shells to be complete. So what happens is that the sodium then donates it's electrons chloride which then accepts it. And this forms an ionic bond. Now um you may I ask well, okay if it's giving away electron then how is that forming a bond? Well, it's not just the giving away of the electron that allows the formation of the bond. But what happens is when the electron is given away sodium becomes positively charged and chloride and able to see this, let me change it positively charged and chloride becomes negatively charged and as positive and negatively charged things attract each other. This ionic bond is formed. So we actually give these ions different names. So sodium is going to be called a cat ion and that's because it's positively charged. Whereas chloride will be given we name an ion which is negatively charged. And like I said, they're attracted to each other by their charges after they either donate or accept an electron. Now, ionic bonds are weak, So they're around 1-5 kilocalories per mole. Remember in cell biology, we use kilocalories, not killer jewels, which you'll see more often in chemistry. Um and they are easily dissolved in water. So that's ionic bond. So let's talk about another type of non violent bond. So a second one that's a hydrogen bond. Now these are formed through attractions between a hydrogen atom and electro negative atom. After you remember back, we've talked about what electro negative atoms are, but just as a reminder their atoms that sort of unequally share electrons, they are more negative because they take in more of the electron's negative charge. So in hydrogen bonds, the partial positive charge of the hydrogen attracts the electro negative atom and they are extremely important in providing water. Its properties will scroll down and we can look at this water molecule here. So, um one of the properties that hydrogen bonding allows water to do is actually dissolving different molecules and water depends on its ability to create hydrogen bonds. And the second property is that it actually results in attraction between water molecules with julie. Remember we've referred to before as cohesion. So hydrogen bonds are also weak, 1-2 kilocalories per mole. So we have this water molecule here, and you can see that it has hydrogen um and oxygen's and the hydrogen has this partial positive charge. And the oxygen, which is electro negative, has this negative charge. And so the hydrogen bonds in this image, you can see here, and it's because these positive and negative charges are interacting. So these are hydrogen bonds which are non violent. So now let's move on to a third, A third type of non covalin bonds. And that's actually Vander wal's attractions. Now, Vander Waals attractions the best way to describe them as these sort of non specific attractive forces that happen when two atoms approach each other. So as things move towards each other, they become slightly more attracted and will continue to move towards each other. Now, Vanderbilt is interesting because it can occur in polar molecules, which is what we've dealt with before with water. Um And these charged molecules like salt, but it also can happen in non polar molecules or in molecules which share their electrons equally. And um the strength of the bond actually decreases with distance of the atoms. Um And so they're very weak as well. One killer calorie from all the weakest bond that we've talked about so far. So you can imagine two molecules moving towards each other. The strength of the bond increases, but then g th let me spell that right? And then as molecules move away from each other, then the strength decreases. Now that's not really so far, I've been showing you these very like chemical um descriptions of chemical images of these bonds happening, but for Vander wal's, because it's this sort of non specific attractive force that occurs when molecules are moving towards each other. I can't really show you a stationary image that can really demonstrate Van der walls forces that happen when things are moving. So um I just want to give you a real life example of andere walls forces. And that is actually has to do with the sticky nature of gecko toes. So, geckos are able to sort of attached to things because their feet are kind of sticky and they can call up surfaces or actually hang upside down because their um little little paws or feet um actually can have Vander wal's attractions to whatever substance there planning to. And that actually gives them this sticky nature. So we talked about these three nonviolent bonds, ionic binding, hydrogen bonding, and Vander Waals forces. So now let's move on

Okay, so now we're gonna talk about some attractive forces and just some overarching concepts that have to do with bonding and cell biology. So um one really important attractive force in cell biology is the hydrophobic effect. And this explains attraction between you guess it hydrophobic molecules. And so hydrophobic if you remember our molecules that do not dissolve in water while hydrophobic molecules do, we're dealing with hydrophobic molecules and hydrophobic effect. And so we know that when we put oil and water that it doesn't really dissolve, oil is hydrophobic, but it not only doesn't dissolve, it actually aggregate and it will separate to form water on the bottom and oil on the top and this aggregation is due to the hydrophobic effect. So how does this happen? Well first hydrophobic molecules have a neutral charge um and therefore cannot form hydrogen bonds and water and therefore do not dissolve in water. And so um but when hydrophobic molecules are put into water, they're surrounded by water molecules which are participating in hydrogen bonding with each other. So there's all these hydrogen bonds going on around them but they can't participate. And so because they can't participate, they actually um group together in these sort of these oil droplets. If you will these hydrophobic droplets attracting to each other because they can't interact with hydrogen bonds that are going on around them. So one example of this in biology and cell biology are hydrocarbons which are non polar their molecules and their hydrophobic molecules made up of hydrogen and carbon and we're gonna talk about hydrocarbons a lot moving forward. Um and so because they are non polar and hydrophobic when they're in water, they actually form these really important cellular structures. So we're gonna talk about this a lot. I just wanted to introduce them but let's take a look at what the hydrophobic effect looks like. So um these blue molecules here are water, oh whereas this big fat brown looking thing is a hydrophobic molecule phobic molecule. Now when these are dropped into water it doesn't make sense for all of these water molecules to take up so much of their energy forming these structures around these hydrophobic molecules. So instead what happens and what is um the best um way to form um the hydrophobic attraction with using the less amount of energy is actually through the hydrophobic effect which makes these hydrophobic molecules come together. And then the water molecules that are forming hydrogen bonds can do so easily and actually with less energy. And so this is an example of the hydrophobic effect. Now we've talked about different types of um bonds and the reason that we did this isn't just because I think you should know them even though you should, but you would have learned these in chemistry. But the reason that we've talked about these bonds is because they're important for the formation of biological structures that we're going to talk about a lot in this course. Now when property of some of these bonds are for instance is non government bonds are weak individually. We know this by themselves. They are very weak but in cell biology they can be added together to form these really strong forces that can even be stronger than co violent interactions. Um whereas individually they're weak but together they're strong. So for instance, DNA molecules are actually held together by non co valent bonds, but D. N. A. Is really stable. I mean we know we can extract DNA from dinosaur bones from forever ago um that has withstood this length of time until now. The reason it can is because it has a combination of nonverbal interactions that make these bonds really strong. Now some molecules we're talking about bonding actually can fit together like a lock and key. So this is um can be termed molecular complementarity which have telesis here because some of you may need to know that some of you may see it in your textbook and some of you may never see this in your book at all. Um but really it describes the walk and key model which all of you will hear about eventually and that is really just a perfect fit between the properties of two molecules. Now we don't typically talk about this in terms of, you know, a carbon atom binding two hydrogen atoms, but instead we talk about one protein or one molecule binding to another one and these are usually larger structures and they have the ability to form all different types of bonds. And when they can form these bonds perfectly with each other they have molecular complementarity and they fit together like a lock and key. So you can see here this molecule here is shaped perfectly for the binding side of this molecule. So when they come together they fit together like a lock key and they show molecular complementarity. Um And another term that we're gonna be talking about a lot in the future. That has to do with this is actually affinity and affinity is determined by how well these two molecules are. More molecules fit together so the higher the fit the higher the affinity so the more they fit together, the more bonds they form, the stronger that connection is the higher the affinity. Um So now let's move on.