LIPIDS AND MEMBRANES

all right so in the previous in the previous meetings we have turn our attention to the proteins and to the enzymes and we learned that proteins and enzymes are are um are important bi molecules in the sense that they enzymes for example catalyze or speed up chemical reactions important biological reactions in the body but would otherwise not occur under normal conditions of temperature and pressure the activity the enzymes is very much necessary for the proper operation of cells of tissues and in fact of a living system proteins themselves enzymes or proteins proteins um perform a wide array of different functions and this functions depend by and large on their structure all right structure function relationship that we have been talking about for a long for the longest time during our prelims is core to the to the study of biochemistry now today's um synchronous lecture I would like to I would like to discuss on the U the um um carbohydrates as well as the lipids there there are um there are four different kinds of biomolecules and you're already aware of what these are um you've already discussed we've already discussed one the proteins the other two or the other three are the nucleic acids and the lipids as well as the carbohydrates in today's discussion we're going to focus our attention on the lipids as well as the carbohydrates hopefully we're going to be able to finish all of them now the um important thing about the um lipids is that this class of molecules are a class of their own that is they they snuff common about the molecules that belong to Glass lipids other than the fact that they are insoluble in water in other words these are the substances that have been grouped or lumped together because of the fact that they are hydrophobic and that they do not dissolve in water all right some people might believe that lipids are actually very boring substances but that is not true all right a number of important a number of important processes biological processes and biochemical reactions are based in the activity of the lipids in fact the cell membrane if you will remember the cell membrane it's the it's the um structure that separates the interior of the cell from its environment the cell membrane um is primarily comprised of lipid by layer all right and you're going to study exactly what the lipid by layer is in a in um in today's discussion okay all right so lipids and proteins are associated in biological membranes okay now first and foremost as I was saying a while ago lipids are heterogeneous class of naturally occurring organic compounds heterogeneous meaning they have so different structures the only thing common to them is their solubility properties they insoluble in water but soluble in arotic organic solvents in solvents like dialer chloroform methyl and chloride and acetone in other words they tend to dissolve in substances that are either insoluble in water or that dissolve to a lesser extent in water we call this substances this lipids hydrophobic now they are emphatic in nature all right what does that mean amphiphatic means that molecules of lipids well natur not all but some of the molecules of lipids have polar heads and non-polar tails and whenever a substance has such characteristic you call that amphiphatic that is it's able to interact with polar molecules like water to also able to interact with non-polar molecules like oil like hexan for example now lipids include open chain forms like we're going to see specially sodium metabolism fatty acids like trial glycerol the Singo lipids fosl glycerols glycolipids this glycolipids for example as well as the fingol lipids are important components of a cell membrane and we're going to discuss um their substances later now many of the vitamines that you're familiar with say for example vitamin D vitamin A this um this um um vitamins remember those vitamins a fat soluble or the lipid soluble vitamins vitamins a d e and K this vitamins are actually lipids all right they are lipids or um that's why we call them lipid soluble vitamins them being lipids are soluble in other lipids now prostag glines if you will remember I think it was in the um where was it in the exam I think it was in the exam or in one of your homeworks I'm not sure if it was in the exam or one of your homeworks mentioned something about the prostag gland yeah I think it was in the um in the salt exercise on enzymes remember the cyc oxygenase the prostag glanding RV pain chemicals and if you want to to minimize pain then you will have to lower the amount of prandin that your body are producing and so prostag glines are lipids like lucrin and the thumb boxin all right um other examples what we've discussed so far the open chain form the cyclic forms of lipids or cyclic or both lipids with cyclic structures include cholesterol the steroid hormones for example the U um testosterone as well as the estrogen and progesterone these are are lipids all right and bile acids those that are of course secreted um um in association with a bile okay so first let us consider the fatty acids fatty acids are organic acids it's meaning they are carboxilic acids a fatty acid is an Branch chain carboxilic acid is most commonly comprised of 12 to 20 carbons derived from the hydrolysis of animal fats all right vegetable oils or FAL for dial gals of biological membranes again we're going to study phosphasal gals later in the shorthand notation for ftic acids right the number of carbons and the number of double Bonds in the chain are shown with by two numbers separated by colon all right these are the fatty acids and what do you notice of the fatty acids okay I'm going to use my pointer you see here the fatty acids are comprised of what carboxilic acid that is a CO as well as a hydrocarbon tail how many carbons do you have here 1 2 3 4 five 6 7 8 9 10 11 12 13 14 15 16 that is a 16 carbon fatty acid all right and what is that called it's called palmitic acid all right if you have a teen that's called steric acid this is oleic acid now what is oleic acid OIC acid has a double bond that position and you have lolic acid you have alpha linolenic acid and you have arachidonic acid now notice that these substances have the same or have not exactly the same structure but they have the same structural feature they have hydrocarbon Tails as well as a carboxilic acid um um um head polar head as well as a as a non-polar tail they differ only in the length in very length and number of carbons that they have as well as whether they have double bonds or not okay all right notice that the double bonds that you can see in the structures are actually cyst double bonds I know that the structure is quite small but if you look at it you're going to notice that the structure is which you're seeing here have Cy double bonds not trans double bonds okay as I've mentioned a while ago the um um there is um a notation that we used for for naming um fatty acids and we're going to look at that later for now lent of fatty acid um um plays a role in its chemical character usually um they usually contain an even number of carbons and assuming that we're going to have enough time we're going to learn the future why um fatty acids typically have an even number of carbon atoms they can contain odd number depending on how they are biosynthesized but it is quite um the number of uh odd-numbered fatty acid is not as many as uh that of the even numbered fatty acids all right fatty acids that contain carbon carbon double bonds are unsaturated right remember those that have multiple bonds are called unsaturated fatty acids if contain only carbon carbon bonds then they are saturated in other words if we do not have carbon carb carbon carbon double bonds then they are saturated all right you see here a typical examples of naturally occurring saturated fatty acids what does that mean that means that they do not have any double bonds so for example look at the number of carbons 12 14 16 18 20 all of these are even numbered fatty acids right and look at their structure you have um here the structure of lauric acid you have the structure of meristic acid structure of palmitic acid steric acid and aritic acid look at their melting points their melting points increases or increase accordingly from 44 to 58 63 71 to 77 degrees celsus and why is that the case that is because as the number of carbon atoms or as the as the size of a molecule increases the strength of interaction between um the uh molecules increases as well that means that the interactions between the molecules tend to become stronger as the molecules become larger that is London dispersion forces if you remember it's dependent and the size of a molecule all right okay now I want you to be familiar with the U names as well as a structure for example you say lorric acid then you will say Ah that's a 12 carbon um fatty acid saturated fatty acid if it's palmitic acid then that is a 16 carbon 16 carbon saturated fatty acids all right okay um in most unsaturated fatty acids those that contain carbon carbon double bonds the CIS isomer predominates and the trans isomer is actually very rare right unsaturated fatty acids sub low melting points and their saturated counterparts why is this the case this is the case because the double bonds s double bonds effectively introduce Kinks or bends into the structure of a molecule prevents the molecules of the fatty acids from effectively packing with we packing close um together right so the packing efficiency of the um unsaturated fatty acids those that have double bonds um tend to be we tend to be uh less effective and therefore the uh melting point is lower for the corresponding or compared to the corresponding saturated fatty acid for example look at at poic acid look here palic acid is a 16 carbon fatty acid and look at its melting point its melting point is negative 0.5 degre C now what does that mean it means at at room temperature 25 de C th