[Music] hi this is andre from med school eu and we're going to begin our course with section 2 of the imat which is biology and we're going to start right from the top of the imat specifications with the unit of the chemistry of living things which is simply biochemistry and the first topic that we'll cover in this video will be the biological importance of weak interactions all right so before we dive into weak interactions we must first brush up on a little bit of on basic chemistry and atomic structure so here we have two atoms sodium and chlorine and first we must know how atoms exchange electrons in order to form interactions and form bonds within each other which is just a theoretical basis of weak non-covalent interactions that we'll talk about in this topic everybody should be already familiar with the structure of the atom there are electrons on this atom and you should know that the most outer shell is called the valence shell which contains electrons on it that are called valence electrons now the octet rule here states that atoms have the tendency to prefer to have eight valence electrons in its most outer shell which means that atoms are stable when they have eight valence electrons and typically when they're stable they're unreactive they do not react very well however these these atoms here they don't have they don't fulfill the octet rule they don't have eight valence electrons because sodium only has this one electron here and chlorine has seven electrons in its valence shell so both of them do not have do not fulfill the octet rule now if if two atoms do not fulfill the octet rule they're typically unstable and if they are unstable they're looking to become stable and therefore they're open to be reactive all right so what happens when two unstable atoms come in contact with each other is that they form interactions so typically when a sodium and a chlorine atom come together the sodium electron here has the tendency to be given up and transferred over to the chlorine now why is that well because when sodium gives up its elec valence electron it actually forms the second shell as the valence shell instead of its most outer shell so it drops down to the second shell being the valence shell and this one has eight electrons which fulfills the octet rule now why does chlorine want to gain this one electron well because it has seven electrons in its most outer shell and by adding one more it becomes stable fulfilling the octet rule and this is the typical basis of how two atoms become stable and form interactions and this is the basis of how weak non-covalent interactions occur so now let's dive into our specific topic on the imat which is weak interactions in living now atoms and biomolecules are typically held together by covalent bonds covalent uh which are strong interactions that involve sharing of electrons now non-covalent interactions are weak interactions so basically another name for weak interactions that are specified on the on the imat they're also known as non-covalent interactions and if these non-covalent interactions occur in large numbers they create a cumulative effect because on their own they're very weak if you have just one non-covalent interaction the attraction between the two molecules or the two atoms will be weak and it's easily broken however when they occur in large numbers they form a cumulative effect and therefore they become very powerful so let's take a look at a uh the the four types of weak interactions that typically occur in organisms and here are the four types number one ionic interactions two hydrogen bonds van der waal interactions and the last one we'll look at is hydrophobic interactions all right so let's begin first with ionic interactions as the first weak interaction that we're going to take a look at now ionic interactions are electrostatic interactions that occur between charged particles now what what do we mean by that well it's basically two charged atoms or molecules that come in contact with each other and they form interactions that are electrostatic meaning there's charges involved so the typical example we have already looked at is the sodium and chlorine where the the two atoms would come in close proximity to each other and what occurs is that the sodium electron is being transferred over to the chlorine shell and then they both become stable however these two atoms they they're charged particles the they're charged atoms the sodium has the tendency to lose this electrons this electron which which means it has a positive charge and the chlorine has a tendency to gain an electron in order to fulfill the octet rule and it has a negative charge and obviously everybody should know the universal role that opposite charges they attract and same charges rebel and this is just a universal principle uh with uh with chemical bonds another thing to know about ionic interactions that they're strongest in a vacuum medium however ionic interactions are typically weaker in aqueous environments so when they're surrounded in water because water tends to separate the two charges that are in close proximity so water comes between these charges and making them separate further apart because water typically also interacts with the positive and the negative charges as well which makes them less attracted to each other and if we take a look at where these ionic interactions uh occur in bodies and human bodies and other organisms most prominently they occur in as an example states here is the amino acids so this there's two amino acids here lysine and glutamic or glutamate glutamic acid or glutamate and these two are amino acids and some amino acids have charges on them so lysine as you can see has a positive charge on this nitrogen end and glutamic acid has a negative charge on the end and the what happens is when these two charges come in close proximity when these two amino acids come in close proximity with each other they form electrostatic interactions that are called ionic interactions so this is an ionic interaction between two charged particles next we'll discuss hydrogen bonds which is another weak interaction that occurs in organic systems and the hydrogen bonds occur when hydrogen is covalently bound to an electronegative atom and i'll explain what this means but first let's let's take a look at what electronegative atom is well typically we learned in school that electronegative atom uh that form hydrogen bonds are fon so fluorine oxygen nitrogen however in biological systems typically you would see oxygen nitrogen and sulfur more often than phone however the the the baseline is that electronegative atoms are atoms that are very attracted to electrons they tend to want to gain an extra electron as we saw with with the chlorine atom so let's let's look at an example what occurs and how these uh hydrogen bonds happen well basically we have two covalently bound hydrogens uh molecules hydrogen bond hydrogen atoms bonded to a molecule with an electronegative atom so there's two of these and when these two molecules come together they uh they tend to form hydrogen bonds now how does this happen well that occurs through uh this notion of dipoles actually so because oxygen is more electronegative it tends to hoard hydrogen's electrons and takes it tends to take it away so it forms a partially negative charge now same thing happens with this oxygen here and the hydrogen would form a partially positive charge and well as you can see what happens with these partial charges occurring is that the negative partial charge and the positive char partial charge would attract each other and form something called a hydrogen bond now where do these hydrogen bonds occur in biological systems well most prominently and and most consistently we see them in dna base bearing so a dna double helix molecule with base pair there are four at c g so there are four nitrogenous bases adenine would base pair with thymine and cytosine would would base pair with guanine and what happens how do they interact while they form hydrogen bonds as you can see here thymine and adenine would form two hydrogen bonds together and this is how they interact and how a dna double helix remains a double helix it's very difficult to disrupt a dna structure because there's so many of these hydrogen bonds that form a cumulative effect that we have talked about previously now let's uh let's talk about the third weak interaction and that would be the van der waals interactions so van der waals interactions occur between two uncharged atoms that approach each other and typically their attraction between the two uncharged atoms is due to permanent transient or induced dipoles and i'm going to explain what that is with an example however before we get to that i first wanted to explain that the two uncharged atoms only interact and form these dipoles at a specific distance between each other so if we have two molecules here they they must be at a specific distance between each other in order to form these van der waal interactions and this distance is called the van der waals radius now if the two particles are closer than the van der waals radius they will tend to repel each other and they will not be attracted and then if they are obviously too far apart then they're not approaching each other and they won't fall form these dipoles so let's take a look at examples of the three most common types of van der waal interactions that are called that are based on dipoles first we're going to take a look at dipole dipole interactions now how this one occurs is is that the the two molecules of carbon double bonded to an oxygen the two molecules approach each other at the van der waals radius and what happens is because these two uncharged molecules are in this proximity they tend to form partial charges so let's label partial charges to these to these atoms now we know that oxygen is more electronegative than carbon uh it is all based on the periodic table and the position of the of the atoms so oxygen here is more electronegative same thing with this oxygen more electronegative so we're going to put a negative charge here whoops negative charge and another negative charge and what occurs with the carbons obviously is uh they become partially positive partially positive and we put a positive charge and as you can see the this forms a dipole that's going in in this direction because of the negative and the positive that interact with each other and this van der waal interaction is called dipole-dipole interaction the next example we're going to take a look at is is very similar however this one's called dipole-induced dipole interaction and this one is a little bit different in terms of how the dipoles are formed now again the same thing happens as these molecules the oxygen atom is more electronegative so therefore because it has a negative partial charge what happens with with let's label this carbon it's positive what happens with these molecules here is that because of this partial charge on the oxygen and this molecule approaching the other molecule at the van der waals radius what actually occurs is that it induces a dipole on this molecule now typically carbon and hydrogen do not form dipoles on their own they do not have charges on their own even partial charges are are not very strong on their own now because of this other molecule that's beside it it is inducing a dipole in this molecule so that they they attract and they become they interact with each other so what we have here is the hydrogens begin to give up its electron to the carbon in order to interact with the negative charge of the oxygen here with this dipole on the other side and of course the carbon then has a partially negative charge and this again forms the same type of dipole as as in the previous example now if we take a look at the last example here we have a these two molecules that are the same as we saw earlier with with the three hydrogens and how they form dipoles is uh is quite interesting so what they have is these two molecules come together at the van der waals radius and typically again both of these molecules are uncharged and they don't even form partial charges on their own however when these two molecules come in contact at the van der waals radius they form partial charges and because otherwise they would repel each other but instead what happens is when these two collide or or come close in contact with at the van der waals radius one of these molecules forms a partial charge so we'll pick the right side molecule will will have this hydrogens give up electrons to the carbon which would form a partially positive charge on the hydrogen side and therefore this carbon would have a partially negative charge now what happens with the hydrogens on this side is of course because of this induced dipole you have another induced dipole on this side and the hydrogens will start to pull electrons from the carbon forming a negative charge and the carbon obviously has given up at some of its electrons and it forms a partial positive charge and this is how van der waals interactions occur through induced dipoles the last type of weak interaction we're going to discuss is called hydrophobic interactions and hydrophobic interactions typically form between nonpolar molecules in aqueous environments so in water and how how hydrophobic interactions occur is best described with an illustration so what we have here is uh this these three non-polar molecules that are thrown into an aqueous environment and as you can see what occurs here is that the three nonpolar molecules they tend to stick together in order to to push the water out and to have the smallest surface area interacting with with the water so this interaction results from the exclusion of water molecules and it works best because it it minimizes the interaction of the nonpolar molecules with water molecules and we're going to see this occur a lot in the formation of 3d tertiary so three prime protein structure where there's plenty of hydrophobic interactions occurring because proteins must form a specific structure or shape in order to function and these these formations largely occur due to hydrophobic interactions to exclude water from interacting inside the protein while it's forming its 3d shape so in the next video we're going to discuss the organic molecules in organisms and their respective functions [Music] you