lipids are a next type of biological molecule and the big thing that sets the lipids apart from the other types of molecules is the fact that they are all nonpolar we're gonna see a few different types of lipids examples of lipids but they all have this in common they're all nonpolar hydrocarbon molecules and consequently they are hydrophobic they don't like to mix with water let's take a look at an example of a lipid triglyceride this is the type of lipid that is present in a lot of foods and triglycerides what they consist of is a glycerol molecule and three fatty acid chains attached to it so this is a very generic triglycer triglyceride structure up here we're going to focus in on these fatty acid chains for just a moment and look at some possible variations on them so these fatty acid chains they can be either saturated or unsaturated and what that means what that's referring to is the type of bonding that's present between the carbon atoms in that chain so if you look at this schematic right here what's being shown right here is a fatty acid chain where all of the carbons have formed the maximum amount of bonds possible we would say that this chain is saturated it has the most hydrogens attached to it that it possibly can if you compare that with this structure down below we have some double bonds that show up in this chain and so consequently there's a potential here there's a potential for these carbons to form even more bonds they could take on some more hydrogens and so this structure we would say is unsaturated it has not been saturated with hydrogens yet this structure the fact that there are double bonds present this tends to lead to bends in the chain so instead of being a straight chain there might be a spot where it bends like that and consequently these chains if you imagine a whole bunch of them sort of like packed up against each other they're simply not going to pack very well and so unsaturated fats tend to be liquid more so than saturated fats so if you think of like butter versus oil butter would be an example of a saturated fat oil it's perhaps not saturated if we're talking about like olive oil okay so those are some triglycerides examples of things that we might see in triglycerides hydrolysis of triglycerides this is what our bodies do in order to break down triglycerides and harvest energy from them so these chains these fatty acid chains this is where there's a lot of energy stored the triglycerides are are a major source of energy for our bodies okay so um the fatty acid chains store a lot of energy and when our bodies break these chains down for one thing it does release energy but for another we tend to form what are called ketone bodies we'll be seeing ketone bodies in a later chapter but ketone bodies they're processed they're formed by the liver and then they end up floating through the bloodstream and ketone bodies are something that affect the ph of the blood so this is something that becomes a concern in the case of if somebody is for example doing a no carb diet a strict no-carb diet where they don't eat any carbs well what's the body going to use as an energy source then if there are no carbs available then the body is going to have to resort to using the lipids so it's going to carry out hydrolysis of fatty acid chains this is going to end up leading to potentially a lot of ketone bodies being formed which will change the ph of the blood and that can be a very dangerous thing this can lead to it's called ketoacidosis it's just the blood gets too acidic and the body can't regulate it quickly enough to keep up and so that can be a very serious problem that can lead to coma and even death if it's not treated quickly enough so that's something if a person is on a no carb diet they would want to watch out for the early signs of ketosis early signs would be a change in the breath like if the people around you start commenting oh your breath smells kind of fruity that would be really one of the first indications of this change this build-up of ketone bodies taking place so anyway that's kind of an aside we've just recapped some information about triglycerides major energy source we'll be coming back to these a little bit later on when we talk about metabolism another type of lipid that we will be seeing are the phospholipids these should be familiar phospholipids are primarily what make up cell membranes and if we just take a look at the structure of a phospholipid it's kind of similar to a triglyceride okay but instead of having three chains now we just have two chains and the other thing that's very different is the fact that there is a phosphate group attached right here this phosphate group makes the molecule have a polar region to it and because of that phospholipids can have let me just point down to this figure these phosphate head groups can interact with water they are happy to interact with water because they are polar so these can end up forming special structures when they're placed in aqueous conditions for example cell membranes yet another type of lipid is the prostaglandin prostaglandins are used as communication molecules they're messenger molecules that can be used between cells and they're a relatively quick form of communication that doesn't require um it doesn't require waiting on a whole lot of circulation to happen it's a quick communication that can be sent from one cell to another nearby cell so prostaglandins we'll see these later on they help to do things like regulate blood vessel diameter that's very important when it comes to controlling blood pressure they also come up in a lot of other places as well we'll learn about blood clotting in some detail so keep in mind prostaglandins are another yet another type of lipid finally our last type of lipid that we're going to mention right now are the steroids steroids are non-polar in keeping with characteristics of lipids but other than that they're actually quite different their structure is very different from the other lipids if you just take a look at the structure over here you'll notice the rings all of these carbon rings that are involved there are four carbon rings um three of them are six carbon rings and the other one is a five carbon ring that's very characteristic of steroids a great example of a steroid is cholesterol and cholesterol as it happens ends up being a precursor for a lot of other types of steroids for example testosterone and estrogen both of those are derived from cholesterol one more reminder just about cholesterol it is a component in animal cell membranes it has a very important role in helping to mediate how fluid the membrane is the more cholesterol that's packed into a cell membrane the more rigid that membrane will be so its levels have to be controlled somewhat carefully in the body cholesterol is also used for making some vitamins vitamin d is listed right here vitamin d is needed in order for our bodies to be able to process calcium correctly and incorporate it into our bone structures so lots of different roles for cholesterol we'll be seeing that later on in the course