WJEC GCE BIOLOGY Carbohydrates 2.6

WJEC GCE BIOLOGY Carbohydrates Carbohydrates are made from CARBON, HYDROGEN and OXYGEN FUNCTION 2:Plant cell walls depend on the STRUCTURAL role of some carbohydrates FUNCTION 1:They STORE ENERGY in plants and animals MONOSACCHARIDES CARBOHYDRATES POLYSACCHARIDESDISACCHARIDES

WJEC GCE BIOLOGY Carbohydrates (CH 2 O) n 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 What does the ‘n’ stand for? Number of Carbon atoms So, when n=3 TRIOSE, e.g. glyceraldehyde - In metabolic reactions When n=5 When n=6 HEXOSE, e.g. glucose - main source of energy PENTOSE, e.g. ribose – formation of nucleic acid next

WJEC GCE BIOLOGY Carbohydrates MONOSACCHARIDES

WJEC GCE BIOLOGY Carbohydrates Monosaccharides can exist as straight chain and ring forms. The ring forms are common when glucose is in solution.

WJEC GCE BIOLOGY Carbohydrates Isomerism in Glucose C 6 H 12 O 6 CH 2 OH Alpha-glucose beta-glucose Show structural change Oxygen Hydrogen Carbon Hydroxide (OH) Glucose forms two isomers They both have the same molecular formula but a different structure

WJEC GCE BIOLOGY Carbohydrates Both these molecules are glucose. Both have a molecular formula of C 6 H 12 O 6. But they are structurally different.

WJEC GCE BIOLOGY Carbohydrates 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 As building blocks….. Repeated glucose molecules build up; starch & glycogen Ribose (5C) forms part RNA Deoxyribose (5C) forms part DNA Biological role of monosaccharides

WJEC GCE BIOLOGY Carbohydrates GLUCOSE MALTOSESUCROSE GLUCOSE Disaccharides A disaccharide can be made from two of the same monosaccharide molecule or from two different ones. Disaccharides form when two monosaccharide units join forming a glycosidic bond, by a condensation reaction. The combination of monosaccharides determines which disaccharide is formed. MONOSACCHARIDESDISACCHARIDE FRUCTOSEGALACTOSE WATER LACTOSE GLUCOSE

WJEC GCE BIOLOGY Carbohydrates Most common disaccharides MonosaccharideDisaccharideFound in ! Glucose and glucoseMaltoseMalt sugar Glucose and fructoseSucroseCane sugar Glucose and galactose LactoseMilk sugar

WJEC GCE BIOLOGY Carbohydrates O OH Forming Disaccharides C C C CO C H OH H H CH 2 OH H H C C C CO C H OH H H CH 2 OH H H C C C CO C H OH H H CH 2 OH H H C C C CO C H OH H H CH 2 OH H H O HH Glycosidic Bond This is a CONDENSATION reaction, where a water molecule is lost. Glucose Maltose

WJEC GCE BIOLOGY Carbohydrates Polysaccharides Polysaccharides are large complex molecules known as POLYMERS. Monomers are the individual monosaccharides which join to form the polysaccharide. Polymerisation is the process of bonding many MONOMERS by condensation reactions to form one large molecule. Return to isomerism of glucose Return to isomerism of glucose Next What is polymerisation ? What is a monomer? Click the bubble for the answer

WJEC GCE BIOLOGY Carbohydrates O OH Forming polysaccharides C C C CO C H OH H H CH 2 OH H H C C C CO C H OH H H CH 2 OH H H O HH In this example, 3 condensation reactions have produced 3 water molecules to produce the polysaccharide. O HH C C C CO C H OH H H CH 2 OH H H C C C CO C H OH H H CH 2 OH H H OH Glucose O O HH O A HYDROLYSIS reaction (addition of water) reverses the reaction and splits the polysaccharide releasing 3 monosaccharide molecules.

WJEC GCE BIOLOGY Carbohydrates 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 STARCHCELLULOSEGLYCOGEN

WJEC GCE BIOLOGY Carbohydrates Starch Made up of two types of polysaccharide; 1)Amylose 2) Amylopectin Amylose Condensation reactions between alpha glucose (1- 4 glycosidic links). Forms a coiled helix

WJEC GCE BIOLOGY Carbohydrates Starch Amylopectin Condensation reactions between alpha glucose (1-4 glycosidic links). Branches of 1-6 glycosidic links also exist. Coiled springs with a branched structure are formed.

WJEC GCE BIOLOGY Carbohydrates

WJEC GCE BIOLOGY Carbohydrates Starch grains are a mixture of amylose & amylopectin Starch is a polysaccharide Starch it is a insoluble store of glucose Starch is only found in plant cells, the animal equivalent is called GLYCOGEN. It is ideal as a storage molecule because: It is compact Insoluble Has no osmotic effect Is readily broken down to mono and disaccharides

WJEC GCE BIOLOGY Carbohydrates GLYCOGEN is the storage polysaccharide in animals 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

WJEC GCE BIOLOGY Carbohydrates Cellulose C1-4 links make up this polysaccharide. If C1 and C4 are to react, one glucose molecule needs to flip through 180 o. It is this subtle difference that make cellulose so strong!

WJEC GCE BIOLOGY Carbohydrates Cellulose Long straight chains of polysaccharides linked together by hydrogen bonds It is the hydrogen bonding between the straight chains that helps to give cellulose it’s strength. Hydrogen bonds are formed between the hydroxyl groups of adjacent parallel chains

WJEC GCE BIOLOGY Carbohydrates 70 chains of β glucose combine to form a MICROFIBRIL. Lots of MICROFIBRILS are held together to form FIBRILS.

WJEC GCE BIOLOGY Carbohydrates Chitin Forms the exoskeletons of insects- lightweight and waterproof Similar to cellulose but also has amino acids to form a mucopolysaccharide The OH groups are replaced by amino acids

WJEC GCE BIOLOGY Carbohydrates You can give this question a go, in order to prove your understanding: