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Carbohydrates WJEC GCE BIOLOGY Carbohydrates 2.6 Carbohydrates Carbohydrates are made from CARBON, HYDROGEN and OXYGEN FUNCTION 1:They STORE ENERGY in plants and animals FUNCTION 2:Plant cell walls depend on the STRUCTURAL role of some carbohydrates MONOSACCHARIDES Carbohydrates WJEC GCE BIOLOGY CARBOHYDRATES DISACCHARIDES POLYSACCHARIDES Monosaccharides Monosaccharides are small organic molecules used as bulding blocks for more complex carbohydrates. Click each of the blue boxes to work through the slide. General Formula (CH2O)n So, when n=3 Carbohydrates WJEC GCE BIOLOGY When n=5 What does the ‘n’ stand for? Number of Carbon atoms TRIOSE, e.g. glyceraldehyde In metabolic reactions When n=6 PENTOSE, e.g. ribose – HEXOSE, e.g. glucose - formation of nucleic acid main source of energy next Carbohydrates WJEC GCE BIOLOGY MONOSACCHARIDES Monosaccharides can exist as straight chain and ring forms. Carbohydrates WJEC GCE BIOLOGY The ring forms are common when glucose is in solution. Isomerism in Glucose C6H12O6 Alpha-glucose CH2OH Oxygen Hydrogen Carbon Glucose forms two isomers Hydroxide (OH) beta-glucose Carbohydrates WJEC GCE BIOLOGY CH2OH Show structural change They both have the same molecular formula but a different structure Carbohydrates WJEC GCE BIOLOGY Both these molecules are glucose. Both have a molecular formula of C6H12O6. But they are structurally different. Biological role of monosaccharides As an energy source….. •A large amount of energy is stored between the C-H bonds •This is released to form ATP •ATP is the energy currency of the cell Carbohydrates WJEC GCE BIOLOGY As building blocks….. •Repeated glucose molecules build up; starch & glycogen •Ribose (5C) forms part RNA •Deoxyribose (5C) forms part DNA Disaccharides Disaccharides form when two monosaccharide units join forming a glycosidic bond, by a condensation reaction. A disaccharide can be made from two of the same monosaccharide molecule or from two different ones. The combination of monosaccharides determines which disaccharide is formed. MONOSACCHARIDES DISACCHARIDE WATER SUCROSE MALTOSE Carbohydrates WJEC GCE BIOLOGY GLUCOSE GLUCOSE GALACTOSE FRUCTOSE GLUCOSE LACTOSE Carbohydrates WJEC GCE BIOLOGY Most common disaccharides Monosaccharide Disaccharide Found in ! Glucose and glucose Maltose Malt sugar Glucose and fructose Sucrose Cane sugar Glucose and galactose Milk sugar Lactose Forming Disaccharides Glucose CH2OH CH2OH CH2OH H C OH C O H OH H C C H OH H H C C OH OH C O H OH H C C C H OH H OH Maltose CH2OH H C Carbohydrates WJEC GCE BIOLOGY OH C CH2OH O H OH H C C H OH H H C C OH OOH H H Glycosidic Bond C O H OH H C C C H OH H OH This is a CONDENSATION reaction, where a water molecule is lost. Polysaccharides Polysaccharides are large complex molecules known as POLYMERS. What is polymerisation ? Click the bubble for the answer Carbohydrates WJEC GCE BIOLOGY Polymerisation is the process of bonding many MONOMERS by condensation reactions to form one large molecule. Return to isomerism of glucose What is a monomer? Monomers are the individual monosaccharides which join to form the polysaccharide. Next Forming polysaccharides Glucose CH2OH H C OH C CH2OH O H OH H C C H OH H H C OH H C O OH H C CH2OH O H OH H C C H OH H H C OH H C O OH H C CH2OH O H OH H C C H OH H H C OH H C O OH H C O H OH H C C C H OH H Carbohydrates WJEC GCE BIOLOGY In this example, 3 condensation reactions have produced 3 water molecules to produce the polysaccharide. A HYDROLYSIS reaction (addition of water) reverses the reaction and splits the polysaccharide releasing 3 monosaccharide molecules. OH Polysaccharides • Polymers with subunits of monosaccharides • Repeated condensation reactions • Normally 1000’s of monomers • Polysaccharides are not sugars • Polysaccharides are insoluble • They are used for storage or construction Carbohydrates WJEC GCE BIOLOGY STARCH CELLULOSE GLYCOGEN Starch • Made up of two types of polysaccharide; 1) Amylose 2) Amylopectin Carbohydrates WJEC GCE BIOLOGY Amylose • Condensation reactions between alpha glucose (14 glycosidic links). • Forms a coiled helix Starch Amylopectin • Condensation reactions between alpha glucose (1-4 glycosidic links). • Branches of 1-6 glycosidic links also exist. • Coiled springs with a Carbohydrates WJEC GCE BIOLOGY branched structure formed. are Carbohydrates WJEC GCE BIOLOGY Starch grains are a mixture of amylose & amylopectin Starch is a polysaccharide Starch it is a insoluble store of glucose Carbohydrates WJEC GCE BIOLOGY It is ideal as a storage molecule because: • It is compact • Insoluble • Has no osmotic effect • Is readily broken down to mono and disaccharides Starch is only found in plant cells, the animal equivalent is called GLYCOGEN. GLYCOGEN is the storage polysaccharide in animals Carbohydrates WJEC GCE BIOLOGY It has 1-4 glycosidic links and 1-6 glycosidic links It is similar to amylopectin but has a greater number of shorter side branches Cellulose Carbohydrates WJEC GCE BIOLOGY • C1-4 links make up this polysaccharide. • If C1 and C4 are to react, one glucose molecule needs to flip through 180o. • It is this subtle difference that make cellulose so strong! Cellulose It is the hydrogen bonding between the straight chains that helps to give cellulose it’s strength. Carbohydrates WJEC GCE BIOLOGY Long straight chains of polysaccharides linked together by hydrogen bonds Hydrogen bonds are formed between the hydroxyl groups of adjacent parallel chains Carbohydrates WJEC GCE BIOLOGY 70 chains of β glucose combine to form a MICROFIBRIL. Lots of MICROFIBRILS are held together to form FIBRILS. Chitin Carbohydrates WJEC GCE BIOLOGY • Forms the exoskeletons of insectslightweight and waterproof • Similar to cellulose but also has amino acids to form a mucopolysaccharide • The OH groups are replaced by amino acids Carbohydrates WJEC GCE BIOLOGY You can give this question a go, in order to prove your understanding: