this key concept video is about the structure and function of carbohydrates and lipids by the end of it we will have covered the structure and function of carbohydrates examples of key carbohydrates condensation and hydris reactions structure and function of lipids and examples of key lipids carbohydrates contain the elements carbon hydrogen and oxygen and their main role is to provide energy through respiration the main substrate of respiration being glucose a monosaccharide some polysaccharides also provide energy storage for example glycogen and starch and some have structural roles for example cellulose in plant cell walls monosaccharides are the most basic unit of carbohydrates they have the general formula CN h2n o n hexoses for example glucose fruct and galactose contain six carbon atoms pentoses for example ribos and deoxy ribos have five carbon atoms glucose is a particularly important monosaccharide in nature it can be completely broken down in aerobic respiration to form a large number of ATP molecules it is the main product of photosynthesis and it is soluble making it easy to transport glucose is also a very stable structure Al from beta glucose molecules are different Animas they have the same molecular formula and same structural arrangement of atoms except for the orientation of the hydroxy group at the first carbon atom in alpha glucose the hydroxy group is orientated downwards where in beta glucose it is orientated upwards this difference results in different Bond formations and so different overall structure and properties of the resulting polysaccharide it also means they are hydrolized by different enzymes now let's look at disaccharides disaccharides are formed when two monosaccharides join together here are some examples moltos is formed from two glucose molecules lactose is made from glucose and galactose and sucrose is made from glucose and fructose note that although fructose forms a pentagon shape in its ring form it is actually a hexo sugar here is carbon 1 then Carbon 2 3 four five and finally carbon six here but how do monosaccharides join together well let's look at this diagram here this shows two alpha glucose molecules here you can see the hydroxy group on carbon one of this first glucose and here you can see the hydroxy group on the carbon 4 on the second glucose molecule this is where Bond formation will Ur between carbon 1 and carbon 4 the bond formed between monosaccharides is called a glycosidic linkage or Bond because it is between the carbon one of one glucose and the carbon 4 of the second glucose this is known as a one for glycosidic linkage two hydrogen atoms and one oxygen atom from the original hydroxy groups that are not used in the bond are released as a water molecule because water is given off this is a condensation reaction to split the moltos up to produce the original glucose molecules water has to be added in a hydrolysis reaction Hydro water lices to split the water molecules provide the hydrogen atom and hydroxy group that were lost during the condensation reaction this reaction we see here is making a larger molecule from two smaller ones so this is also known as an anabolic reaction and it requires an input of energy catabolic reactions break larger molecules down into smaller ones with the release of energy more monosaccharides can be added to this Mose in the same way through condensation reactions to form a polysaccharide such as starch which brings us very nicely onto polysaccharides the storage carbohydrate of plants and animals are starch and glycogen respectively starch is made of made up of two different polysaccharides Amo and amop peptin Amo is an unbranched polysaccharide made up of alpha glucose molecules joined together by Alpha 14 glycidic linkages this long amalo chain coils to form a more compact molecule amop pactin is also made up of alpha glucose molecules but this time it is a branched polysaccharide because as well as alpha4 glycidic linkages there are alpha6 glycosidic linkages together these two molecules form starch starch is insoluble and the branching makes it more Compact and easily broken down by the enzyme amalay so this makes it an ideal storage carbohydrate of plants glycogen is a polysaccharide made up of alpha glucose molecules again it is highly branched due to the numerous alpha6 gly aidic linkages it is the major storage carbohydrate of animals and is ideal for this role as it is insoluble inert and compact it needs to be more highly branched than amop pectin as animals are more metabolically active so need glucose to be released more rapidly when it is required the more branches there are the more ends there are for the enzymes to hydroly the glycogen cellulose is composed of beta glucose molecules joined together by beta4 glycosidic linkages the beta glucose molecules are alternately rotated through 180° thereby forming a straight unbranched chain then you can see here many hydrogen bonds form between hydroxy groups of different glucose molecules in the same chain and also between adjacent cellulose chains forming fibral bundles of fibral together form fibers like string making up rope this structure gives cellulose its strength to be the main structural component of the cell wall imp plants we've now come to the end of carbohydrates and can move on to the next group of biological molecules the lipids lipids are not polymers as they are not made up of repeating monomer units they are usually insoluble in water but soluble in less polar organic solvents such as ethanol lipids in include fats oils steroids and waxes like carbohydrates they contain the elements carbon hydrogen and oxygen but with less oxygen atoms than carbohydrates we are going to look at triglycerides phospholipids and steroids triglycerides are made up of three fatty acids attached to a glycerol molecule as you can see here this is a glycerol molecule and alcohol these are the three fatty acid molecules each fatty acid molecule is made up of two parts the carboxy group and a hydrocarbon chain the hydrocarbon chain can be saturated or unsaturated when there is one carbon carbon double bond they are called monounsaturated if they have more than one double bond they are polyunsaturated double bonds put a kink into the chain which pushes the molecules apart lowering their melting point and making the lipid more fluid lipids with many unsaturated fatty acids are usually oils and are often found as energy stores in Plants those with mainly saturated fatty acid tails are often fats and found as energy stores in animals so how are triglycerides formed well like polysaccharides they are formed by the formation of calent bonds this time between the fatty acids and glycerol molecule via condensation reactions during this reaction three water molecules are released due to the Three fatty acids forming calent bonds known as EST bonds with the glycerol again like with carbohydrates a triglyceride can easily be broken back down into its constituent molecules by hydrolysis reactions catalyzed by the enzyme lipase thus making them good energy stores as well as energy storage triglycerides can be used for thermal insulation protection of major organs and buoyancy in aquatic mammals similar to triglycerides are the phospholipids these have a phosphate group replacing one of the fatty acid Tails here is the phosphate group R represents choline you can see it is charged so it is hydrophilic the fatty acid tails are hydrophobic therefore phospholipids are amphipathic this amphipathic property is important in the of phospholipids in the cell membrane the phospholipids orientate themselves in a Bayer with their phosphate groups facing outwards in the aquous environment and the fatty acid Tails protected in the center fatty acids and phospholipids may still be saturated or unsaturated unsaturated fatty acids make a more fluid membrane as they push the molecules apart organisms can control the fluidity of their membranes using this feature those that live in cold climates tend to have more unsaturated fatty acids ensuring their membranes remain fluid in low temperatures cholesterol is a steroid and it has a completely different structure to triglycerides and phospholipids it has a polar head group a fused ring structure in the middle and a flexible nonpolar tail down here it is found in membranes with its polar hydroxy group interacting with the phosphate heads and the hydrophobic middle and tail sitting between the fatty acid tails of the phospholipids at higher temperatures cholesterol reduces membrane fluidity by disrupting the phospholipids from moving too freely at lower temperatures cholesterol increases fluidity by preventing the phospholipid Tails from packing too closely together cholesterol is also used to form the steroid hormones such as all estrogens including estradi and testosterone steroid hormones can pass through the cell me membrane to reach their target receptor site inside the nucleus so now that we've looked at carbohydrates and lipids the key points to take away are that condensation reactions are responsible for making larger molecules from smaller molecules such as polysaccharides from monosaccharides and triglycerides from Three fatty acids and glycerol they result in the formation of calent bonds in carbohydrates these are glycosidic linkages and in lipids they are Ester bonds starch made up of amalo and amop pectin and glycogen are storage carbohydrates of plants and animals respectively both molecules are made of alpha glucose and branches are formed by alpha6 linkages cellulose is a structural carbohydrate and is made up of beta glucose its strength is enhanced by hydrogen bonds between glucose molecules of the same chain and different chains phospholipids and cholesterol are amphipathic and this is really important in the structure of the cell membrane the saturation of the fatty acid tailes of the phosph lipids and the presence of cholesterol help control the fluidity of the cell membrane