1 BIOLOGY PRESENTATIONS FOR A-LEVEL, IN MULTIMEDIA JAMES BOWLES, 2001 BIOLOGY PRESENTATIONS FOR A-LEVEL, IN MULTIMEDIA JAMES BOWLES, 2001 LEFT CLICK OR PRESS SPACE BAR TO ADVANCE, PRESS P BUTTON TO GO BACK, PRESS ESC BUTTON TO END LEFT CLICK OR PRESS SPACE BAR TO ADVANCE, PRESS P BUTTON TO GO BACK, PRESS ESC BUTTON TO END

2 ‘A’ Level Biology Carbohydrates

3 Carbon Nucleus contains 6 protons and 6 neutrons.

4 Surrounded by 6 electrons (4 in outer shell) It is, therefore capable of forming 4 stable covalent bonds (Tetravalent) Carbon

5 Nucleus contains 6 protons and 6 neutrons. It is, therefore capable of forming 4 stable covalent bonds (Tetravalent) It is able to form covalent bonds with other carbon atoms, allowing it to form the backbone of biomolecules Carbon Surrounded by 6 electrons (4 in outer shell)

6 Nucleus contains 6 protons and 6 neutrons. It is, therefore capable of forming 4 stable covalent bonds (Tetravalent) It is able to form covalent bonds with other carbon atoms, allowing it to form the backbone of biomolecules Carbon Surrounded by 6 electrons (4 in outer shell)

7 Carbohydrates Most abundant (by mass) biomolecule in nature

8 Most abundant (by mass) biomolecule in nature Contain: Carbon Oxygen Hydrogen Simplest formula is (CH 2 O)n

9 Glucose 6 Carbons 6 Oxygens 12 Hydrogens C 6 H 12 O 6

(C 6 H 12 O 6 ) For convenience carbons are numbered, starting with the one with the aldehyde group Glucose

11 (C 6 H 12 O 6 ) Glucose This is optical isomerism 222 Carbons are asymmetric since OH and H and can be on either side 22222

12 Ring Formation Aldehyde group on carbon 1 bonds with hydroxyl group on carbon 5 (C 6 H 12 O 6 ) Glucose

14 Carbon 1 is now asymmetrical

15  Glucose There are two forms of glucose in ring structure

16  Glucose There are two forms of glucose in ring structure

18 CH 2 OH For simplicity not all the components are shown

19 Glycosidic Bond CH 2 OH Monosaccharides join via an oxygen bridge between carbon 1 and carbon 4 of adjacent sugars

20 Glycosidic Bond CH 2 OH The bond involves the two hydroxyl groups

21 CH 2 OH Glycosidic Bond Water is produced - this is a CONDENSATION reaction

22 CH 2 OH Glycosidic Bond The reverse of this is HYDROLYSIS

23 CH 2 OH The reverse of this is HYDROLYSIS Glycosidic Bond

24 Disaccharides 1 4 CH 2 OH Maltose Found in germinating seeds and the alimentary canal – breakdown of starch  Glucose  1-4 Glycosidic bond

25 Disaccharides Sucrose Found in sugar beet and sugar cane  Glucose Fructose  1-2 Glycosidic bond 1 CH 2 OH

26 Disaccharides 1 4 CH 2 OH Lactose Found in Milk  Galactose  Glucose  1-4 Glycosidic bond

27 Testing for Reducing Sugars

281. Combine equal quantities of test solution and Benedict’s reagent in a test tube Testing for Reducing Sugars

292. Warm in a water bath Testing for Reducing Sugars

30 Testing for Reducing Sugars 3. Change in colour and opacity indicate the reducing sugar concentration

31 Testing for Non-Reducing Sugars CH 2 OH Hydrolyse the glycosidic bond with warm dilute HCl

32 2. Neutralise with NaHCO 3 Testing for Non-Reducing Sugars 3. Perform a Benedict’s test

33 Polysaccharides - Starch CH 2 OH 2 components to starch : Amylose and Amylopectin Amylose is an unbranched molecule of glucose units bound by 1 – 4 glycosidic bonds

34 Polysaccharides - Starch The chain of glucose molecules arranges itself as a helix

35 Polysaccharides - Starch The chain of glucose molecules arranges itself as a helix The bore of which is the same size as a molecule of iodine in KI

36 Polysaccharides - Starch Amylopectin is a branched molecule with 1-4 glycosidic bonds, And occasional 1-6 bonds forming branches

37 Polysaccharides - Starch Branches arise every 25 th 25 th or so glucose molecule

38 Polysaccharides - Glycogen glucose units joined by 1-4 and 1-6 glycosidic bonds Similar structure to amylopectin, but with more frequent branching

 glucose Polysaccharides - Cellulose

Polysaccharides - Cellulose Straight chain molecule of 1-4 glycosidic bonds, stabilised by hydrogen bonds between adjacent glucoses

41Hydrogen bonds also exist between adjacent chains – molecule of high tensile strength Polysaccharides - Cellulose

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