lipids is another major group of biomolecules that we will look at in this course lipids are all hydrophobic molecules they don't like water they are insoluble in water can be esterified to become more hydrophobic but they do not form polymers there are two classes of lipids that are either derived from fatty acids or isopinoids fatty acids give rise to several types of lipids including triges worlds which are the storage form of lipids they can be broken down to release energy waxes are highly hydrophobic and they serve as lubricant or waterproof surfaces glycerol phospholipids and sphingolipids are membrane lipids they are the major components forming the lipid by layer in cell membranes and organelle membranes icosinoids a group of signaling molecules activating a variety of physiological responses in our body lipids derived from isoprenoids include steroids such as cholesterol and a number of steroid hormones some lipid soluble vitamins are also derived from isoprenoids and terpenes are a large class of natural products in many different organisms fatty acids and isoprenoids are structurally unrelated the only thing they share in common is that they are hydrophobic these two groups of lipids are often associated with each other in living tissues and food items because of their common physical properties let's begin with fatty acids they are the simplest form of lipids they contain a carboxylic group and this is actually a carboxylic acid with a long hydrocarbon chain there are different names for the different components the whole structure is fatty acid if the carboxylic acid is esserified with something else this functional group is referred as a fatty acyl group and this long chain is a hydrocarbon tail there are two different nomenclatures for fatty acids in the iupac system the carboxyl carbon is the number one carbon then number two number three number four then all the way down to number 12 in this example but in traditional organic chemistry the carbon attached with the carboxyl group is uh designated as the alpha carbon followed by the beta gamma so on and so forth okay now the very large carbon regardless of the number of carbons is always designated as the omega carbon in greek omega is the last alphabet these are some are common fatty acids so with their common names many of them are getting their names from the sources where they were first identified pretty much like the case for many amino acids for example lowrage is i was first isolated from the l'oreal plant okay palmite was first isolated from palm oil okay but subsequently many of these factory acids were also found to be present in different organisms including human an important physical property in fatty acids is the melting point which determines whether they would occur as liquid or solid at room temperature there are two parameters that are affecting the melting point of fatty acids the first one is the number of carbons increasing the carbon number in the hydro carbon chain is going to increase the melting point the second parameter is the number of double bonds along the hydrocarbon chain as as you can see down here increasing the number of double bonds is going to decrease the melting point drastically let's compare two fatty acids with equal number of carbons arachidate okay with 20 carbons no double bonds our ketonate with 20 carbons again but four double bonds and you can see that the melting point for age is 75 degrees but with the presence of four double bonds in our dominate the melting point drops to minus 49 okay again they have the same number of carbons okay so that will result in very very different uh physical appearances at room temperature so our rocket date will be very solid whereas our kedonate would be liquid at room temperature a saturated fatty acid contains no double bonds along the hydrocarbon chain if there is one or more than one double bond along the hydrocarbon chain we call that an unsaturated fatty acid so the double bond is always occurring in the cis configuration okay so the presence of a cis double bond is creating a band okay along the hydrocarbon chain in a mixture of saturated fatty acids the hydrocarbon chains between the neighboring molecules are packed nicely together with very strong hydrophobic interaction okay therefore it will require a lot of energy to break them apart resulting in a higher melting point okay now the presence of unsaturated fatty acid would weaken the interactions because of the bending created by the six double bonds okay consequently it won't require that much energy to break them apart resulting in a much lower melting point in the lipid mask mixture containing unsaturated fatty acids about fatty acid nomenclature steric acid the one on the left here it is a saturated fatty acid no double bonds so there is a shorthand notation for fatty acids so in this case we put 18 okay which indicates the number of carbon so there are 18 carbons no double bonds so we put a zero after the codon here okay so 18 0 represents the fatty acid having 18 carbon no double bonds oleic acid okay this one it is a monounsaturated fatty acid that means there is one double bond okay again it has 18 carbon one double bond and this delta nine the number in superscript uh indicates the first carbon that is having a double bond okay so here the the double bond is formed between the number nine and number ten carbon okay so we always put the first carbon okay uh after the delta in superscript okay linoleic acid is called polyunsaturated factory exit so when there is more than one double bond along the hydrocarbon chain we call it a polyunsaturated fatty acid so again there are 18 carbon two double bonds and these are the two positions for the double bonds at the number nine and number 12 carbon this linoleic acid is also called uh n omega-6 okay fatty acids so omega-6 or n6 these two mean the same thing so remember the omega carbon is the very last carbon so what does omega-6 mean it means that the sixth carbon from the omega n so one two three four five six the sixth carbon from the omega and is having the first double bond okay so we call that an omega-6 fatty acid ninolic acid is an essential fatty acid do you still remember what essential amino acids mean okay it is the same meaning essential fatty acid like nino lake acid has to be obtained from our diet because we do not have the ability to synthesize uh linoleic acid okay so that's why we call it an essential fatty acid alphanolanic acid is another essential fatty acid we have to obtain it from our diet it is also a polyunsaturated fatty acid that contains three double bonds along the hydrocarbon chain at position number 9 12 and 15. it is regarded as an omega-3 fatty acid as you can see from here the third carbon from the omega end is having the first double bond therefore it is an omega-3 fatty acid you probably have heard before about omega-6 and omega-3 fatty acids okay so they are commonly found in some health supplements they have been uh heavily advertised for their health beneficial effects okay now you know what they mean now okay so next time uh you know you can show off by drawing their structures telling people what these omega-6 and omega-3 fatty acid mean as i just said polyunsaturated fatty acids are commonly used as health supplements so one of the those products is fish oil omega-3 okay so these are containing omega-3 factory acids that are extracted from fish oil the two major uh ingredients are epa and dha okay the structures are shown on the right here there we got it as long chain body and saturated fatty acids so there are a large number of carbons along these hydrocarbon chain and i think you should know now why they're called omega-3 fatty acids and based on these structures can you provide the shorthand notations for epa and dha and i also want you to look up their health benefits why are they important for uh for health okay please look that up on your own okay another product commonly supplemented with lipids is this infant formula the milk powder for babies so again i would like you to look up the lipid composition in particular the polyunsaturated fatty acids that are found in these uh milk powder so next time when you go to a drugstore or please look that up on the on the from the navel and also find out what might be the health benefits for those polyunsaturated fatty acid supplements in living organisms fatty acids are stored in the form of triazole gize roads which are also called triazole glycerides it is formed from a good gestural molecule and each of these o h group is esterified with a fatty acid so it's shown down here is the molecule of uh triazole glycerol so there are three fatty acid chain okay so these are ester linkages these fatty acids okay are often not the same as the example shown on the right here so they contain different number of carbons and different number of double bonds so this is the name for this triazole gizmo so these three are referring to the three different fatty acid chain triazology rules are stored in fat cells called adipocytes these are fat globus fat globules are filling up the entire cells okay they are found underneath our skin serum or surrounding our internal organs providing a layer of insulation in addition the fat cells can be used as a source of energy so when needed the triazole gizmos can be released and broken down for the production of energy food fats or lipids and fats are mixtures of triazole gizmos with various fatty acid composition so looking at this frying pan there are three types of food fats so these three and can you tell which one is which you probably know right this is olive oil butter and beef fat okay at room temperature apparently they have very different physical appearances this is actually affected by the fatty acid composition so if we look at olive oil you can see that it contains a very large amount of unsaturated fatty acid so that is going to reduce the melting point for olive oil okay drastically and that's why it appears as liquid at room temperature on the other hand b fat it contains more of the saturated fatty acids okay so that would increase the melting point of b fats okay and that's why it appears as solid okay at room temperature and butter is in between these two okay and and that can be reflected by the fatty acid composition as well okay it is a sort of intermediate between these two and that's why it appears more solid than olive oil but more liquid compared to beef fat this chart shows the proportion of saturated monos unsaturated and polyunsaturated fatty acids in different types of lipids generally in the plant oil there is higher percentages of unsaturated fatty acids including monounsaturated and polyunsaturated fatty acids and the amounts of saturated fatty acids are lower so that's why plant oil generally appears as liquid at room temperature because the melting point has been reduced due to the large amounts of unsaturated fatty acids animal fats on the other hand okay contains a much smaller amounts of unsaturated fatty acids with increased amount of saturated fatty acids so therefore they appear more solid at room temperature due to the increased melting point okay interestingly there is uh some plant oil like a pump palm kernel oil and coconut oil they contain very high percentages of saturated fatty acid okay and very low amounts of unsaturated fatty acids you may notice that coconut oil okay can solidify very easily especially during cooler days okay and because the melting point is very high okay if you uh need to you know use coconut for cooking you probably need to warm it up first okay to make it liquid now generally saturated fats okay or lipids with more saturated fatty acids are considered to be unhealthy because the saturated fatty acids has been shown to increase the risk of cardiovascular diseases on the other hand the unsaturated fatty acids are considered to be more healthy because they would reduce the risk of cardiovascular diseases another lipid that is commonly found in food is cholesterol and of course cholesterol is almost always associated with bad health again it has to do with increasing the risk of cardiovascular diseases okay so cholesterol structurally is very different from fatty acids but it is often associated with fatty acids or triazole gizmos in food okay but cholesterol is only present in animals okay so when you are eating animal fats okay so you're eating triaxial gizzards with high levels of saturated fatty acid together with some cholesterol okay on the other hand there is no cholesterol in plant oil because plants do not make cholesterol okay in recent years certain infant formula milk powder has been advertised to contain uh the body friendly sn2 palmitate what exactly is that it is a triazole gizero with the second carbon in the gizro backbone that is esterified with a poematic action that's why it is called sn2 palmitate it is claimed that tetsen ii palmite is body friendly because this is present in human milk the lipids and the milk produced by dairy cattle have a very different fatty acid composition so presumably since this is present in human milk sn2 palmette would be better utilized or assimilated by babies trans fatty acids are considered to be bad for health because they increase the cholesterol and tries on glycerol levels in blood and that would increase the risk of cardiovascular diseases so what are trans fatty acids they are containing double bonds along the hydrocarbon chain now in naturally occurring unsaturated fatty acid like oleic acid the double bond is always in the cis configuration so that a bend or twist will be formed in the hydrocarbon chain but in the trans fatty acid the double bond is in the chance configuration like what is shown here so in a sense it is not affecting the overall structure in the acell chain or the hydrocarbon chain okay so based on that which one of them will be having a higher melting point it should be the chance fatty accent so why would trans fatty acids be present in our food they are actually produced by hydrogenation of vegetable or plant oil the hydrogenation serves to reduce these double bond implant oil okay to become [Music] saturated okay so these process would increase the melting point of the hydrogenated plant oil would become more solid and spreadable like butter a good example would be margarine however hydrogenation of plant oil comes with a side reaction that converts some of this cis double bond into chance double bonds so the formation of chance double bond would not affect the overall structure of the acellj because the chance configuration results in an extended chain just like a saturated hydrocarbon chain because margarine is derived from palm oil some people may think that it is more healthy than butter but the presence of trans fatty acid is making margarine unhealthy nowadays in all food labels the amounts of trans fatty acids have to be indicated because they are known to be a risk factor for human health icosanoids are important molecules responsible for a variety of physiological processes they are made from fatty acids specifically they are oxygenated derivatives of 20 carbon polyunsaturated fatty acids so shown below are three examples they all have a 20 carbon fatty acid backbone with these uh different numbers of double bonds and also different degrees of oxygenation along the fatty acid backbone prostaglandin is responsible for blood vessel constriction from boxing is required for blood clotting nucleotide is required for a smooth muscle contraction in nucleotide okay so again this is the fatty acid backbone and it is being linked to a dipeptide okay so can you identify which one of the linkage is a peptide bond should be this one okay and then what are waxes they are made from long chain fatty acids esterified with long chain alcohol resulting in a highly hydrophobic structure with a high melting point so wax materials are very solid very hot and waterproof bee wax and earwax are good examples they provide protection and lubrication waxes also provide a waterproof surface on plants like the leaf and fruit surfaces fatty acids also give rise to structural components in biological membranes glycerol phospholipids are the first type of membrane lipid they are phospholipids with a glycerol backbone structurally they are related to triazine glycerols there are two fatty acid chains attached to the first two carbons in this glycerol backbone the third carbon is attached to a polar head through a phosphate therefore they are called phospholipids glycerol phospholipids are the most abundant lipids in biological membranes including plasma membranes and organelle membranes these are some examples of polar head groups the first column indicates the precursor molecules or the sources of the polar head grips and different glycerol phospholipids the polar groups may carry charges positive or negative or they may be having functional groups like hydroxyl group or carbonyl group so all these features are making the polar head hydrophilic in nature let's take a look at a few examples of github phospholipids these are the polar head grips attached through the phosphate at the carbon number three in the glycerol backbone on the other hand the first two carbons are each attached with a fatty acid chain derived from fatty acids so the overall structure contains one polar head and two non-polar tails in biological membranes there are two layers of lipids arranged in the way that the hydrophobic tails are clustered in the middle as a result of their hydrophobic interactions on the other hand the polar heads are exposed on either side to the aqueous environment so now you should understand that the non-polar tail are coming from the fatty acids whereas the polar head are different hydrophilic structural components that are either charged or containing polar functional groups sphingolipids are the second types of membrane lipids which are abundant in nervous tissues in mammals they also contain fatty acids as a structural component ceramide is a precursor for the formation of sphingolipids to make ceramide it requires sphingosine and swingosine is a long chain amino alcohol containing 18 carbons there is an amino group at the number two carbon and two oh groups at the number one and number three carbon ceramide okay which is this one is formed by a reaction between the number two amino group and then a and the fatty acid okay resulting in the attachment of this fatty acid chain through an amine linkage to the amino group so now you can visualize that these two long hydrocarbon chains are the nonpolar tails in the membrane lipid and this number one oh group will be modified by attachment of different polar heads resulting in the formation of simple sprinkle lipids such as galacto cerebral side and glengliocite in galactose cerebral side it has a galactose attached to the number one carbon as the polar head again these two hydrocarbon chains are the two non-polar in the membrane lipid galacto cerebroside is found abundantly in nervous tissues in fact it constitutes about 15 percent of all lipids immigrants shift in glenglue sites the polar head has a more complex structure which is an oligosaccharide containing an amino sugar exit residue called an acetyl neuraminic capsule actually there are more than 60 variety of gland glucides each having a different sugar composition in the oligosaccharide polar head the example shown below is called glengliocite gm2 steroids are the second class of lipids they are structurally different from fatty acids while they are also hydrophobic in nature in the basic structure of steroid there are four rings fields together a well-known example of steroid is cholesterol which is an animal steroid in addition to this multiple ring structure there is an aliphatic tail attached to the d-ring making cholesterol more hydrophobic but there is a little bit of hydrophobic property in cholesterol that is at this number three carbon with a hydroxyl group cholesterol is often associated with fatty acids this c3oh group may be esterified with a fatty acid chain to form cholesterol ester further increasing the hydrophobicity with this very long hydrocarbon tail although cholesterol is often considered to be bad for human health it has many important functions it is only problematic when we have excessive amounts of cholesterol in our body cholesterol is found in membranes and if you flip the structure around you can visualize the oh being a polar head whereas the multiple range with this hydrocarbon chain okay being a hydrophobic structural component as a matter of fact cholesterol can be inserted within a lipid by layer in biological membranes the o-h group is exposed on either side while the hydrophobic component is clustered in the center with the fatty acid chains of membrane lipids interacting with each other through hydrophobic interactions compared to the fatty acid chain the ring structure in cholesterol is more rigid therefore the fluidity and permeability of a membrane can be altered by adjusting the amounts of cholesterol in the lipid by layer another important function for steroids is that they are hormones and we need cholesterol as a precursor to make different types of hormones testosterone and estradiol are male and female sex hormones respectively cortisol are released in response to stress and low blood sugar while aldosterone functions to regulate blood pressure therefore it is important that we have cholesterol in order to be able to synthesize these different steroid hormones cholesterol also provides the backbone for the formation of the lipid soluble vitamin d which is important for our well-being for example it improves calcium absorption in our body these are two versions of vitamin d with different aliphatic side chains vitamin d can be made in our skin okay using structures that are derived from cholesterol uv radiation in the sunlight can cleave okay the b ring at this position okay followed by a spontaneous reaction that produces vitamin d while they may have important functions excessive levels of cholesterol will affect our cardiovascular health this is a cross-section in a coronary artery where cholesterol is accumulating in the internal wall forming a plaque and it also results in inflammation as illustrated on the right here as cholesterol is building up inside the artery a blood flow will be slowing down and ultimately blockage will occur and that's a major cause of heart attack so it will be very dangerous to have too much cholesterol accumulating in the human body cholesterol and triazole gizzaro are both very hydrophobic so they cannot dissolve in blood for delivery throughout the body instead they are packaged inside a macromolecular structure called lipoproteins as the name suggests there are two components in lipoproteins lipids and proteins a single layer of phospholipids form the surface membrane with the polar head exposed on the outside and their hydrophobic tails are pointing internally where the different lipids are packaged there are also proteins and cholesterol integrated in the phospholipid membrane layer lipids that are packaged inside a lipoprotein include triazology roads and cholesterol esters which means cholesterol esterified with fatty acids the polar surface allows lipoproteins to be delivered through the blood stream and there are different types of lipoproteins each having different functional role the two major types of lipoproteins are low density lipoprotein ldl and high density lipoprotein hdl ldl is responsible for depositing cholesterol in tissues including blood vessels on the other hand high density lipoprotein hdl is with responsible for returning cholesterol from different parts of the body to liver where excess cholesterol is degraded to biostore biosalt for removal very often ldl cholesterol is referred as bad cholesterol while hdl cholesterol is referred as good cholesterol structurally it is the same cholesterol that is present in ldl and hdl however if cholesterol is carried inside ldl it is bad because it will be deposited onto body tissues in contrast if cholesterol is carried inside hdl it is good because it will be removed from the body this is a sample report for a blood test to examine the lipid profile in the patient after learning about lipids in this module you should be able to understand all these different items this is total cholesterol and the result here should be staying below this value okay because having too much cholesterol is not good and triglyceride is the same as triaxial glycerol and it should be within this range hdl cholesterol and ldl cholesterol are also tested okay there is a minimum requirement for hdl cholesterol higher values mean that the body is removing extra cholesterol on the other hand there is a maximum value for ldl cholesterol as having too much of it is suggesting that cholesterol is accumulating in body tissues so we want to get above this level for hdl cholesterol but below this value for ldl cholesterol and overall this patient looks um pretty healthy in terms of the elect the profile some correlations have been established between the types of fatty acids in the diet and the cholesterol profile in human body the first three saturated fatty acids commonly found in these food sources would have any effect in increasing both ldl and hdl this is not very desirable because more ldl means higher chance of cholesterol deposition in tissues steric acid by contrast lowers both ldl and hdl it is not desirable either as we need to have more hdl to remove excessive cholesterol olatic acid which is a chance fatty acid generated during hydrogenation of plant oil it increases ldl and decreases hdl this is the worst scenario that's why trans fat reactors are bad for our health as mentioned earlier the amounts of chance fatty acids have to be indicated on the labels for packaged food items the unsaturated fatty actors which are pleasant in plant oil would give rise to a very desirable profile with reduced ldl and increased hdl that's why plant oil are considered to be more healthy so these are correlations between fatty acid types and cholesterol profile in human body but the precise mechanisms are still largely unknown nevertheless these are widely accepted guidelines for people to choose what kind of oil to consume but i have to remind you that fat is still fat if you consume too much of plant oil you still get fat excess lipid will be converted to triazole gizmo for storage in fat cells or at diplo sites and it will stay there forever if you don't exercise okay that would conclude our discussion on lipids thank you