to learn a level biology for free with mr. ik this video is going to be on triglycerides and phospholipids from the biological molecules topic so first of all just have a look at the difference between these two lipids you need to know about they both contain a glycerol molecule which is a three carbon compound and then they contain fatty acids but a tribe is right as the name suggests tri meaning three has three fatty acid chains a phospholipid has only two chains and instead of the third chain that is replaced by a phosphate group so looking at how those molecules are made first we'll the triglycerides so to get the visceral bonded with those three fatty acids it involves three separate condensation reactions so each of the fatty acid chains will go through a condensation reaction with the visceral so we end up with three water's be produced and three ester bonds forming and the ester bond is this they're just here so where we have our carbon oxygen and between just here so just to show you that all together we've got our glycerol we then have three fatty acid chains we said a water molecule is removed so that's why it's a condensation reaction so three water molecules are actually removed and then we end up with our three bonds and three molecules of water so the fatty acid chains we saw those labeled and these sometimes are shown as an R group because the number of carbons and hydrogens can vary so that's why it's an art meaning variable group and there's two three types saturated and unsaturated saturated means that in this hydrocarbon tail all of the carbons only have single bonds between them so they're saturated because they're bonding with as many hydrogen atoms possible unsaturated means you have at least one double bond between the carbons and therefore you're not holding the maximum number of hydrogen atoms each kid but these two sentences here are the exact definitions and I've underlined between the carbons because of the eighth waymark scheme if you don't state that the double bond or single bond is between the carbons you would not get that mark so let's have a look at some of the properties then of the triglycerides so number one these lipids these triglycerides one of their main functions is for energy storage and the reason they store so much energy is because there's a large ratio of a particular type of bond which holds a lot of energy and that is these carbon to hydrogen bonds compared to the number of carbon atoms so because there are so many carbon to hydrogen in that fatty acid tail it stores a lot of energy we also have a high ratio of hydrogen atoms compared to oxygen and this enables it to act as a metabolic water source now what we mean by that is if the triglyceride is broken down and in particular if it's oxidized is able to form water molecules and this is why lots of desert animals store triglycerides say for example camels the hump on their back unlike the misconception is not a hump of water is actually a hump of triglycerides and that will provide water when the triglycerides are oxidized so another property that's a huge advantage is triglycerides because they are so big and they are hydrophobic meaning they repel water so they're insoluble and this means you can store lots and lots of this triglyceride away as an energy storage without affecting the water potential therefore it won't affect osmosis causing too much water to move into the cell making self bursts so as a huge advantage lastly lipids such as triglycerides are relatively low in mass I want to say relatively low I'm comparing that to tissues like muscles for example so muscles are far more dense than lipids and the reason that's an advantage is you can store lots of lipids for this energy storage without making the animal too heavy and therefore restricting their movement all right so let's have a look then at the test of lipids known as the emotion test so you need to dissolve your sample in ethanol so I'm adding some oil here first of all then I'm adding my ethanol and to dissolve shaking it up next you add distilled water and you have to shake again and then finally it's describing what the positive observation looks like and it is white in color and we describe it as an emotion and it's really really importantly use that word not precipitate precipitate means you've made a solid and we haven't made a solid emotion means you have split apart in this case the lipids into such tiny droplets that they're all surrounded by the water that you get this thick liquid consistency that we call an emulsion but it is not solid so White's emulsion is the positive result so lastly then is the phosphate pits so the structure of phospholipids we saw right at the beginning you still have a big strong molecule you still have fatty acids but you only have two so the third fatty acid chain has been replaced by a phosphate group they are created in the same way it'll be condensation reactions between the glycerol and the fatty acids but because we only have two chains they'll only be two ester bonds forming the properties that are quite different because of this phosphate group and we can see here on the phosphate group that we have a negative charge and due to that charge on the phosphate group it gives the property of what we call hydrophilic head my describes as the head so it's a hydrophilic head and that means it's able to attract and interact with water in comparison the fatty acids don't have any charges on them so they are hydrophobic hydrate meaning water phobic meaning fearing now what we mean by that in science is it rebounds so the tails repel water but they're able to mix and interact with lipids now because of those properties phospholipids when they're put into water arrange themselves in this two layer structure which we call the bilayer a phospholipid bilayer and that is the structure that you see on membranes so for example the cell surface membrane but also in eukaryotic cells the membranes on organelles this double layer or bilayer of phospholipids where the tails move inwards because they are repelled by water but they can interact with the lipids and the hydrophilic heads move to the outside because those can interact with water so we do describe phospholipids as being polar because of these two different charged regions so for the lipid just make sure you do know the structure of a triglyceride and phospholipid how they're formed by condensation reaction and the bonds that is made their function the properties that is and how you test for lipids so the emulsion test I hate but you have found this helpful today if you have please give a thumbs up and click the subscribe button to keep up to date on all of the latest videos [Music]