[Music] so what are biological molecules well biological molecules are the building blocks to make cells and other key structures required to make living organisms so in biology it's really the smallest level of detail that we're interested in we really want to know about cells and this is the next level down just understanding how to make a cell you to know about these key molecules that you need to build cells and therefore to build living organisms now as a human you get these molecules through your diet through eating they give you the ability to make more cells and grow provide energy for the processes that happen in your body and they keep you healthy as well the most important three types of molecules you need are carbohydrates lipids and proteins so they are made up of chemical elements these molecules carbohydrates are made up of carbon hydrogen and oxygen that's where you can aim from carbohydrate lipids are also made up of carbon hydrogen oxygen but just in different proportions to make that molecule proteins are made up of carbon hydrogen oxygen and some nitrogen so it's important to remember that you need nitrogen to also make proteins so we're going to go through these three key biological molecules now and learn more about their structure and what we use them for in our bodies so carbohydrates we said made up of carbon hydrogen oxygen and we use them in our bodies for the process of respiration to release energy for all of our metabolic processes for the chemical reactions that happen inside ourselves we get most of our carbohydrate in the form of starch from foods like potato rice and pasta now starch is a large carbohydrate storage molecule that's made by plants animals tend to store their carbohydrate in the form of something called glycogen here is a big long starch molecule it could be many thousands of molecules long and the reason that plants store their their carbohydrates starches because it's insoluble it won't dissolve in water so it won't affect osmosis in their cells and it won't kind of get washed away it's a good storage solution for their carbohydrate therefore if we eat this carbohydrate these big long molecules we need to be able to break it down in our bodies to release the individual single sugar molecules that they're made up of so we need to do that using enzymes in digestion and then we can release the glucose which is the molecule the sink singles the single carbohydrate molecule that we need for respiration lipids now lipids are things like fats and oils also made up of carbon hydrogen oxygen like carbohydrates and food high in animal fats include things like meat and butter cheese milk eggs oily fish part oils tend to be things like olive oil sunflower oil rapeseed oil now a fat is used to make cell membranes in ourselves insulation protection of organs and as a store of energy it has quite a bad name you know people talk about fat being bad for you and you want low foods low in fat but it's very very important that we have fats in our diet I suppose it's just about having the right amount not too many of the fats and also try and get more plant fats in our diet those oils there which are healthier than the animal fats that are listed there okay the structure what does the molecule look like for a fact well it's actually made up of something called a glycerol and then three of these zigzag chains which are called fatty acids and again in order to digest lipids they need to be danny's to be broken down back into the glycerol and into those fatty acids protein now protein is very very important all cells in your body contain protein we'd it for growth and repair of all our tissues animal foods high in protein include meat and fish cheese and eggs and plants tend to contain a less protein but there's still a lot of protein in beans and peas and nuts as well proteins are large large molecules very complex in shape and they are made up of many many little individual amino acids all joined together now there are 20 different types of amino acids and depending on how you arrange them will give the protein its overall structure it's folded up into a very complex 3d shape of protein which then allows to carry out its function all enzymes in your body are made of protein all a lot of your hormones are made of protein you need protein to make a lot of the different structures in your body and in your cells so this is an example of one protein which is made up of 12 different amino acids here and that could there that could be actually hundreds and thousands of amino acids long sometimes and then it can all be folded up to form this beautiful shape here so in summary these are the three major molecules here this is a picture of their shape and what molecules they're made up of which is what you need to know now in this topic there's a few practicals you need to know about and there are some chemical tests that you need to know that you can use to test if these molecules are present in a food sample or not we're going to look at the test for starch and glucose so there's two tests for the different carbohydrates one for start form for glucose and there's a test for protein and there's a test for lipids and fats the test for starch very very simple what you do is you take a small sample of the food you place it on a spotting tile probably on a test tube and you add something called iodine solution now iodine solution starts off as a yellow brown color and if the food contains starch then iodine changes color to blue black in order to test for glucose you need to add at the food to a boiling tube I need to add a solution called Benedict's solution menak solution is a lovely blue color kind of sky-blue color now you need to actually heat up the Benedict's solution and the food sample for the reaction to work so you need to leave in a water bath for about five minutes at about eighty degrees C and if the food sample contains glucose it will change color and it'll go through a series of color change its bet on how much glucose or is if there's a little bit glucose it will go green then it'll go more orange and eventually if there's lots and lots of glucose in the food it will go a brick red color the test for protein is to add a solution called by aret solution now by rekhs solution is also a kind of blue color but when you add it to protein it goes lilac or purple you don't need to do heating or anything you can just add the Pyrex solution straight on to the food sample lipids the last food technician about basically what you do is you add ethanol to the to the to the fat and give it a shake around the fat will dissolve in the ethanol if there is any there then you add some water and shake it again and the fat then comes out of solution and forms are kind of cloudy white emulsion so if you get this cloudy white emulsion then lipids are present so here's a summary table of this very important that you know these food tests know how to carry out these food tests and make sure you have them clear you