so today's topic is about lipids which is the third by a molecule that we're going to talk about so lipids are a class of molecules that have wide variety of functions so when we hear the word lipids oils comes to our mind oils fats you know cholesterol etc etc but you know that cholesterol which is a precursor for a different types of hormones especially our sex hormones that's also falls under lipids some vitamins such as vitamin E and vitamin K are also classified as lipids so here's a here's a picture of olive tree and where we we can extract you know olive oil from all the fruits but you know we know that olive oil is good for the body right but olive oil aside from having the oil molecules itself okay the fatty acids it also contains phenolic compounds so phenolic compounds which act as antioxidant and that is the reason why one of the main reasons why olive oil is good for our body because aside from the oil molecules itself or the fatty acid itself we it also contains phenolic compounds so remember that proteins have wide variety of roles as well but comparing proteins with lipids proteins they basically have the same components right amino acids folded into a 3d structure and you know they can exist as enzyme receptors etcetera etcetera but lipids even lipids as a class of biomolecules they have also wide variety of structures so inside from having lots of different functions they also have different structures so that's why when we define lipids so these are basically molecules that are not soluble insoluble in water but soluble in organic solvents such as hexane right so there are five classes of lipids depending on their functions and also structures so the first one is free fatty acid which is a common fuel and this is actually a fuel which is more in my opinion a better fuel for for the body okay but of course some of some of our human organs use they can switch from between carbohydrates and and fats okay for example brain how our brain can switch between glucose and ketone bodies so ketone bodies are essentially synthesized from from fats okay adipose tissues you know fat cells their main source of energy are basically fatty acids and glucose okay liver they our liver get the energy mainly from fatty acids also but of course it also uses carbohydrates okay but red blood cells is very interesting some red blood cells only rely on lucasz ass it's prime it has its fuel okay so free fatty acid so we will explain why pretty fatty acids always has that word free the word free okay and then so we will explain that a little later the second class is triacylglycerols or try a slope grease right so sometimes you'll you'll see so try a soak this right which is the storage form of fatty acids and then we have the membrane lipids called the phospholipids another membrane lipids which which are a glycol lipids we you encountered this word like a lipids from the previous chapter the carbohydrates chapter remember the last time slides on how viruses toxins are able to recognize cells to be infected right because they recognize the the glycan or the carbohydrate components of glycolipids okay so in this type of lipids we have obviously carbohydrates conjugated to lipid molecules and then the last class is the steroid steroids polycyclic hydrocarbons with variety of functions so let's talk about the first class of lipids which is a which is fatty acids and sometimes we call this free fatty acid the main reason why we use the word free whenever we talk about fatty acids because fatty acids actually come from fats or oils okay so fats and oils fats so these molecules are essentially the same when you look at this their structures the only difference is that facts are solid at room temperature and oils are liquid at room temperature of course there's a different subtle differences in the structure oils have INMO in in most cases so they have some double bonds okay that what makes them a little bit liquidy at room temperature okay and fats are mostly saturated fatty acids meaning all all bonds are single bonds okay so the the main reason we use free fatiah the word free in free fatty acid because you need to free the fatty acid from fats and oils to be able to get this nice structure right here alright so we define fatty acids as basically chains of hydro hype hydrocarbons that has carboxylic acid on one end and a methyl group at the other end okay so that's your ch3 right there so fatty acids essentially it's a long hydrocarbon chain with methyl on one end and carboxylic acid on the other end so you have two forms of fatty acids the saturated in unsaturated when you say unsaturated so there's the presence of sis double bond so this is a system about this is a naturally occurring unsaturation right and of course you you most probably know about the trans trans fat which basically means the fatty acid or the fats or oils have the trans double bond so you might wonder why this is deprotonated because at physiological pH you lose the protons on your carboxylic acid because remember that the carboxylic acid has a pKa of around 3 or 4 okay so since th7 is higher than PK 4 so carboxylic acid will be deprotonated all right so how do we name a fatty acid so essentially we're not gonna learn how to give systematic name and the common name you don't need to memorize any of these but we are going to what we're going to learn is how to abbreviate the name by using either the Delta Delta numbering or Omega numbering of carbons alright so for Delta numbering of carbon carbon skeleton in your fatty acid we essentially use the number of carbons the total number of carbons in your fatty acid okay so for example this Delta numbering 18 semicolon 1 Delta 9 so that means you have 18 carbons total number of carbons and then this number is the number of unsaturation so meaning number of double bonds and the double bond exists between carbon 9 and carbon 10 so you pick the lower number for denoting the position of the double bond and the Delta numbering starts with the carbonyl carbon so carbonyl carbon is always going to be carbon 1 so if you have 16 semicolon to Delta say 9 and 11 so that means you have total the ARP total number of carbon 16 and you got two double bonds the first double bond is between ten and then this is not a good example so 12 so the first double bond is between nine and ten and then the second double bond is between I'm sorry and the second double bond is between carbon 12 and 13 okay so the other method of numbering the carbon is starting from the methyl the terminal methyl and this is called Omega numbering okay so make a numbering so if you have this example 18 semicolon 1 Omega 9 so you start numbering your carbon from the terminal methyl so that will be your carbon 1 and you start counting or to determining the position of the double bonds you start from the methyl end so this will be 1 2 3 4 5 6 7 8 9 so this is carbon 9 sorry carbon 9 with respect to the methyl end so the double bond is between carbon iron and carbon 10 with the methyl and as your reference carbon so in this example so the Delta numbering for this particular fatty acid would be C have a total of 18 carbons semicolon and then you have 1 2 3 4 so 4 unsaturation 4 double bonds and this would be starting from so this is carbon one two three four five six so you have Delta six seven eight nine so nine and then twelve to twelve and so between twelve and thirteen and then you got fifteen okay so for Omega numbering so this would be so you start from this end so 18 semicolon four again but this time you come from the right okay so this would be one two three so make three and then six and then nine and then twelve so for this example on this example this actually called Omega 3 so this is an omega-3 fatty acid okay so the reason why it's called omega 3 fatty acid because you have you start it the double bond starts at carbon three starting from the Omega carbon okay so omega-3 fatty acid could also be if you don't have this is a single bond single bond and single bond that will also be called an omega-3 fatty acid okay so even if you have two double bonds the first between carbon three and four and the second is between carbon six and seven this will also be called omega-3 fatty acid okay but the the Omega numbering would be this in for Delta that will be so these are some natural occurring fatty acid in animals but the most common fatty acid lengths are c16 and c18 okay so 16 carbons and 16 and 18 carbon fatty acid so you have so these are the net some naturally occurring but you can also have less than 12 we can have 10 but 10 and below most probably present in some oils okay so for example coconut oil will have lots of MCTS so MC T's is medium chain triglycerides okay so when you say medium chain triglycerides so most probably lots of Satan and C 1210 carbon and 12 carbon fatty acids okay so you know you'll notice that all these names end with a T right so because again at physiological pH so they are deprotonated so that means they are the conjugate base of the fatty acid okay so lower rate comes from lauric acid myristate comes from the ristic acid decanoic is the decanoic acid it's etc alright for this question this only eight is an omega-9 fatty acid true or false so let's check so omega-9 fatty acid let's see so you start from the metal end so that would be one two three four five six seven eight nine so the answer is true all right for this question what is the abbreviated nomenclature for a ten carbon omega-6 fatty acid so ten carbon omega-6 fatty acid that contains no other double bonds so in other words it's looking for the Delta numbering okay if you have a ten carbon omega-6 fatty acid that only has one double bond so for a ten carbon fatty acid one two three four five six seven eight nine ten okay so you got the methyl on one end and the carboxyl carboxylate on the other end so that will be one two three four five six seven eight nine and ten so carbon omega-6 would be double bond so you have a double bond between six and seven starting from the methyl end okay so the Delta numbering would be one two three four so 10 one semicolon one Delta 4 which is letter C so again so these are the two forms of fatty acids at different physiological up a different PHS so at physiological pH keep in mind that this PK the pKa of carboxylic acid is around four so therefore it will be deprotonated so this form which is called politic acid is exist at pH a very very low pH right should be less than less than four because when pH equals PKA then you're gonna get equal amounts of the protonated and deprotonated form of fatty acid all right so fatty acids differ in terms of their number of carbons and degrees of unsaturation so as I mentioned the most common number of carbons in fatty acids are 16 and 18 and the double bonds is it's this configuration okay that's natural naturally occurring types of double bonds this is so the trans trans configuration is most likely formed when you heat up the oil and/or you do partial hydrogenation so this is this process partially hydrogenating your fatty acid is fairly common done by by companies you know oil come not really oil companies but you know companies that make for example margarine or other types of oil products or or fat products okay so the main reason why they partially hydrogenated oils is because they they become they will have longer shelf-life okay and they will be easy to transport because they are most likely solid at room temperature if you partially hydrogenated hydrogenated oils okay so the only the main problem of personally hydrogenating these oils okay to become semi solid or solid is because it uses very high temperature relatively high temperature which which means that the SIS double bonds will most of them will become trans okay by simply heating the oil so I become trans double bonds and that's actually quite dangerous because it's not recognized by bacteria and therefore oils which are partially hydrogenated will we'll have longer self-life in terms of our human of human health since trans trans trans double bond bonds are not easily recognized borrow bodies so they will tend to accumulate most likely right and they will stay in our system for a longer period of time so again these fatty acids will differ in terms of their chain length and degree of unsaturation and more these double bonds this unsaturation are separate by at least one methylene group so that's that's called one methylene group right there so the because of the the length the length the different lengths and degrees of unsaturation the type of unsaturation said they will have they will have different physical properties such as melting point so if you have this fatty acids to rate and then translate with a trans double bond in assists only so this only eight will have the lowest melting point right because melting point depends on how the molecules are packed together okay in the solid state so since sicily 8 has systolic molecules have this kink because of the presence of cysts double bonds you'll see the kink right there so they will have less packing it in the solid state and therefore they will they can easily melt so they have lower melting point the stearate which is such saturated fatty acid so this will have a high melting point because since the tail the nonpolar tail is this is essentially a linear so they can pack together okay very efficiently so more interaction between the tails and therefore higher temperature higher melting temperature for saturated fatty acid so trans Olli 8 this will also be it will also have high high melting point in terms of these two we don't really differentiate the melting point of these two because some of them probably will have the same melting point on some samples presence of the trans double bond may be a little bit lower but definitely these two so these two molecules will have higher melting point than sis or fatty acid with sis double bonds so what factors determine the melting point of fatty acids so we have the length okay and the degree of unsaturation and the degree of saturation can have a number of sis double bonds or if you also have say presence of trans double bond so what's the consequence of having cysts double bond as opposed to trans double bond configuration so the correct answer is if you have a cysts configuration in your fatty acid it causes a bend or kink in the fatty acid molecule all right so why do we need to to incorporate unsaturated fatty acids getting into our diet so the main reason is that so first let's look at these different types of unsaturated fatty acids starting from alpha linolenic which is most common in olive oil EPA the ICO sub I go serpents and then 10:08 EPA for short and the COS docosahexaenoic DHA so these two are most common commonly found in fish okay so these are essential fatty acids and which means we cannot synthesize these types of fatty acids so olive oil will have lots of alpha linolenic molecule and if you remember I said olive oil aside from having the oil molecule itself which is this alpha linolenic it also has phenolic compounds which are acting as antioxidants but why why are these also very beneficial to our health for example a pollutant aid in olive oil so these molecules are actually precursors for anti-inflammatory molecules so they are involved in the synthesis of these molecules anti-inflammatory molecules okay okay the second type of a second class of lipids we're going to talk about is try a so glycerol so try a so glycerides okay so triacylglycerols are the storage form of fatty acids so in in the Tri a little trace of glycerol molecule so you have the glycerol backbone okay so that's the gross glycerol backbone glycerol is essentially ch2oh and then CH o H and ch2oh so that's glycerol and the numbering of carbons is you start from the top so one carbon one carbon two carbon three so one two and three and these are your fatty acid chains so fatty acids are stored as triacylglycerol so even in oil so olive oil coconut oil if you look at the composition of these oils oil samples most of these oils are in the form of triacylglycerols okay so when the fatty acids so these fatty acids are released from the backbone so they become free okay that's why it's called free fatty acids and when you when you start seeing the release or freeing the fatty acids from kreisel glycerols so that's essential to start off degradation of the oil or triacylglycerols but it's it's pair common that in a sample of oil fats and oils you have about maybe 5 percent 5 percent free fatty acids in the mixture alright but of course mostly the oil molecules or the fat molecules will be mostly in the form of triacylglycerols so the manner at which these fatty acids are attached to the glycerol backbone is through esterification so you have so you can see the ester right there so that's an ester bond that's an ester bond that's also an ester bond okay so these are ester bonds okay so please copy these this light since this is not on your note packet so this is just explaining why fats are more efficient fuel storage storage than glycogen in terms of the energy okay based on the the how much how much ATP or energy you can extract from from fatty acid fatty acid carry more energy produces more energy per carbon because the nonpolar tails are essentially reduced form okay more reduce form then say for example glucose so keep in mind that if a molecule starting it will have more oxygen okay for example if you have glucose with lots of hydroxyl group which OHS and that means the carbon is already partially I'm oxidized right so the the most oxidized form of carbon is essentially co2 okay so that's the most oxidized form you cannot burn or extract energy from co2 because it's already been fully oxidized but if the carbon has oh it is um aldehyde then it's already partially oxidized but you can still burn Oryx you can still extract energy from those molecules so another reason is that fatty acid carry less water because they are essentially nonpolar and this is very beneficial for for animals such as birds okay especially migratory birds because they they don't need but they don't want to carry more water during migration so therefore they actually fatten themselves up by eating foods with high fatty acid content so glucose and glycogen essentially used for short term energy needs and very quick delivery but if you need a long term supply of energy then fats fats are better for that for those situations slow delivery and good storage alright so we stored the triacylglycerol in the fat cell or adipose tissue or a Depot silence and so normally these adipocytes or our fat cells you see this lipid droplet it's actually occupying most of the of the space in the cell and the nucleus which we know is the largest organelle in the cell it's being pushed on the side of the adipose cell alright so essentially it's huge droplet liquid a lipid lipid or fat droplet inside the factitious or fat cells so one example of a very impressive migratory bird is this red red knot which is labeled as b95 was banded okay b95 most probably banded in 1995 I think this is already this bird is ready dead but at this be 95 red knot is also called the moon bird okay moon bird because it travelled a distance which is equivalent to a distance between the Earth and the moon so it they said that this bird lived for at least 2025 years okay very impressive migratory bird all right the next class up lipids that we talked about is membrane lipids so lipids that are incorporated in the cell membrane so the common types of membrane lipids are the phospholipids the geico lipids and cholesterol so these three are present in mammalian cells okay while cholesterol is not present in bacteria in bacterial cells so but lately or recent or recently they discovered some cholesterol like molecules in the cell membrane bacterial cell membranes but it's not a definite classification whether it is really cholesterol molecule or or any add or any or maybe some other type of membrane molecules in bacteria but for now we're gonna will say that this is not present in box cell membrane all right what's the structure of the phospholipid molecules so this is essentially the general components so you have the fatty acids okay fatty acids attached to carbon 1 and carbon two of your glycerol backbone a plat a platinum is ro platformed is also called platform and then you got the phosphate attached to carbon three of your glycerol platform and an alcohol attached to the phosphate and the most common type of platforms in phospholipids are the glycerol which already know and the sphingosine okay so we will you will see the structure of sphingosine a little later so I already showed you the structure of the glycerol so three-carbon visceral backbone so phospholipids with glycerol platform are called phosphoglycerates or forceful glycerol so this is this is called phosphoglycerate base right so these are examples of phosphoglycerates or phosphoglyceraldehyde starting with phosphatidylserine so you have again the two so remember our one is your hydrocarbon nonpolar hydrocarbon chains get connected to carbon 1 and carbon 2 and then you have the platform the visceral platform and then the phosphate and an alcohol is essentially a molecule with an alcohol functional group in this case is stirring so remember serine is an amino acid with an o h h 2o h as the art as it's our sidechain phosphatidylcholine this is the Collin molecule phosphatidyl ethanolamine so that's the ethanol I mean that's the ethanol which the alcohol connect with an amino group okay first petition you know inositol this is Dan Innis atoll molecule and cardiolipin so for this question in phosphoglycerates or phosphoglyceraldehyde e acids okay the our one in the are two in the diagram from the last light arse terrified at glycerol carbons one and two okay carbon three is where you find the phosphate group and the alcohol molecule alright so that's a quick review remember that membrane membrane lipids are essentially of three types you have the phospholipid and then you got the glycolipids and you have the cholesterol alright and under phospholipids you have the phospho glycerides or glycerol and this is the second type thus Pingo lipids okay so both fossil glycerides and sphingolipids are phospholipids so sphingolipids are essentially phospholipids weird sphingosine platform and the spinning platform looks like this okay it's actually a long molecule in a cell so you can see there's a built in it's called the built in a built in nonpolar tails so which means you only need one fatty acid it's terrified and that release terrified this is actually a carboxamide functional group okay so you only have one r1 that's r1 which is your nonpolar tail your nonpolar fatty acid connected to this finger seen platform but you and of course you still have the phosphate and you have the alcohol molecule so the most common type of sphingolipids are the sphingomyelin which is present in myelin sheath of themselves okay and so in nerve cells there will be lots of spin go myelin which is a form of a type of sphingolipids okay so for fastball glycerides phosphoglycerates you need two fatty acids but for sphingolipids you only have you only need one fatty acid change since the sphingosine platform already has a long nonpolar tail all right so this is the second type second type of membrane lipids first one is possible lipids right so this is the second type like a lipids essentially a carbohydrate containing lipids so it's a carbohydrate lipid conjugate and the simplest type of glycolipids are the cerebral sides so that's there is a receiver side it's cerebral sides I mean and as you can see cerebral sides have a sphingosine platform okay one fatty acid unit okay and instead of having the phosphate it has so the sphingosine is attached to a glucose or galactose so that's the simplest type of glycolipids cerebral sides all right so our cell membranes will contain glycolipids as well so glycolipids are commonly recognized by toxins right toxins such as say for example cholera toxin or pertussis toxin so they recognized the glycolipid of the the carbohydrate component of the glycolipids so these toxins recognize these carbohydrates okay in the glycolipid before they they enter the cells alright so the next class of lipids are the steroids steroids have molecules have this nucleus structure which essentially contains consists of three cyclohexane rings in a cyclopentane ring that are fused together and cholesterol is the most common type of steroids and the role the main role of your cholesterol in your cell membrane remember you have the phospholipids the glycol lipids and the cholesterol for a mammalian cell membranes is to to maintain membrane fluidity okay so makes it keeps the salmon very fluid so I will give you the youtube link for animation of how cholesterol is maintaining the fluidity of the cell membrane so this is the structure of the your cholesterol and this is the the nucleus structure this is the polar region of the cholesterol only that OAH right there and this is the rigid for rigid portion of the tail and this is the flexible portion of the tail of the cholesterol molecule alright cholesterol is also a precursor to steroid hormones I such as you know sex hormones progesterone testosterone and cholesterol is also a precursor for vitamin d3 synthesis so if you want your body to produce vitamin d3 okay endogenous vitamin d3 then expose your skin to sun because when cholesterol is hit by UV cholesterol undergoes transition and chemical reaction that makes a precursor for vitamin D okay which is vitamin d3 so all these membrane lipids are called amphipathic molecules one when you say empathetic molecules it has the polar head and nonpolar tail so phosphoglycerate this is the first form of phospholipids right that's the polar head right there in nonpolar tail spin gamelon same thing so this would be the polar head region in nonpolar tail region archaeal archaeal lipid this thus the the type of lipid molecules membrane lipid molecules found in archaea those organisms that live in extreme condition so you got this this type of structure right here the shortened depiction of your membrane lipids sometimes for glycerols can't remember the glycerol backbone I mean I try a service rules which are molecules with three tails so sometimes we we draw the Tri a sub missiles like this okay but for the membrane lipid molecules so it has a polar head and two nonpolar tails and this is your cholesterol again which is all which is also an effective anti patek molecule because of that polar region the Oh H functional group and the nonpolar tail rigid portion and the flexible portion so aside from [Music] carbohydrates that can be covalently bound to lipids okay which you already know that the glycol lipids right you can also have a protein lipid conjugates okay so meaning proteins that are covalently bound to lipids and essentially the main role the main function is the main reason why proteins would be bound to these lipids is to localize the protein to the cell membrane okay so these are just examples GPI anchor is a very common and very interesting type of protein so this is your protein sorry so this is the the protein right here this is because this is the carboxyl terminus of your polypeptide chain and then this is your lipid molecules right here and you have the phosphate the sugar and some other components okay all right if and if you have questions so please send me an email