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1. 2 Introducing carbohydrates Carbohydrates are a group of substances used as both energy sources and structural materials in organisms. All carbohydrates.

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Presentation on theme: "1. 2 Introducing carbohydrates Carbohydrates are a group of substances used as both energy sources and structural materials in organisms. All carbohydrates."— Presentation transcript:

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3 Introducing carbohydrates Carbohydrates are a group of substances used as both energy sources and structural materials in organisms. All carbohydrates contain carbon, hydrogen and oxygen, with the general formula: C x (H 2 O) y. There are three main groups of carbohydrates: monosaccharides – these are simple sugars, with the general formula (CH 2 0) n, where n can be 3–7 disaccharides – these are ‘double sugars’, formed from two monosaccharides polysaccharides – these are large molecules formed from many monosaccharides.

4 Glucose The structure of glucose can be represented in different ways: Glucose is an abundant and very important monosaccharide. It contains six carbon atoms so it is a hexose sugar. Its general formula is C 6 H 12 O 6. Glucose is the major energy source for most cells. It is highly soluble and is the main form in which carbohydrates are transported around the body of animals. straight chain ring ring (simplified)

5 Remembering how to draw α- glucose Remember: LO Hexagon Wings

6 Alpha and beta glucose Glucose exists in different forms called structural isomers. Two common isomers are alpha glucose and beta glucose. alpha glucose beta glucose The only difference between these two isomers is the position of the H and -OH group attached to carbon 1. In α-glucose, H is above the carbon and in β-glucose it is below the carbon. 1 23 4 5 6 1 23 4 5 6 This minor structural difference has a major effect on the biological roles of α and β glucose.

7 Two forms of glucose

8 Fructose and galactose Galactose is not as soluble as glucose and has an important role in the production of glycolipids and glycoproteins. Two other important hexose monosaccharides are fructose and galactose. fructose galactose Fructose is very soluble and is the main sugar in fruits and nectar. It is sweeter than glucose.

9 The formation of disaccharides

10 Maltose, sucrose and lactose Maltose (malt sugar) is formed from two glucose molecules joined by an alpha 1–4 glycosidic bond. Sucrose (table sugar) is formed from glucose and fructose joined by an alpha 1–4 glycosidic bond. Lactose (milk sugar) is formed from galactose and glucose joined by a beta 1–4 glycosidic bond.

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13 Condensation and hydrolysis

14 14 of 30© Boardworks Ltd 2008 What are polysaccharides? Polysaccharides are polymers containing many monosaccharides linked by glycosidic bonds. Like disaccharides, polysaccharides are formed by condensation reactions. The major polysaccharides are starch and cellulose in plants, and glycogen in animals. Polysaccharides are mainly used as an energy store and as structural components of cells.

15 Starch Found in many parts of the plant as small grains. Large amounts in seeds and storage organs Major energy source in most diets Alpha glucose + alpha glucose + alpha glucose + alpha glucose + alpha glucose + alpha glucose + alpha glucose............................. etc. = starch 1000s of glucose molecules bonded together by glycosidic bonds in condensation reactions makes starch

16 Starch: Amylose and Amylopectin 16 The glucose molecules are joined by 1,4 glycosidic bonds. Amylose is alpha glucose, forming straight chains. The chains fold naturally into a helical shape.

17 Starch: Amylose and Amylopectin 17 The branches are made with 1,6 glycosidic bonds. Amylopectin is also alpha glucose, forming branched chains.

18 Starch: Amylose and Amylopectin 18 Starch is a mixture of amylose and amylopectin; it's insoluble and is used as a storage molecule for plants.

19 Starch: Amylopectin 19 Starch is a mixture of amylose and amylopectin; it's insoluble and is used as a storage molecule for plants.

20 The structure of starch

21 Starch Main role of starch is energy storage, something it’s especially suited for because: It is insoluble It is compact When hydrolysed it forms α-glucose Stored as granules What are the advantages of these properties?

22 Properties and uses of starch Starch is the major carbohydrate storage molecule in plants. Starch is produced from glucose made during photosynthesis. It is broken down during respiration to provide energy and is also a source of carbon for producing other molecules. It is usually stored as intracellular starch grains in organelles called plastids. Plastids include green chloroplasts (e.g. in leaves) and colourless amyloplasts (e.g. in potatoes).

23 TASK Discuss/research why each of these features are important and fill in the table Finished? Draw a molecule of amylose and amylopectin on your sheet and start to research Glycogen. 23

24 Starch Glycogen Cellulose Alpha and Beta Glucose Condensation and Hydrolysis Amylose: Made up of _______ glyco_____ chains of _____glucose Amylopectin: Made up of _____ glucose and is branched (1,4 glycosidic bonds) Main role of starch is _______storage, something it’s especially suited for because: FEATUREWhy this is useful It is insoluble Helical shape When hydrolysed it forms α- glucose Stored as granules Glycogen: Made up of very short chains of _____ glucose and is highly branched (1,4 glycosidic bonds) Stored as small granules mainly in the muscles and liver. Readily hydrolysed. Why is this helpful? …………………………………………………………………………………………………………. Draw a diagram of a glycogen molecule here: Forms straight unbranched chains rather a coiled chain like starch or a branched chain like glycogen. Chains run parallel to each other allowing hydrogen bonds to form cross- links between adjacent chains (microfibrils) Provides strength to cellulose cell walls Individual bonds are weak but large numbers adds to considerable strength. Draw a diagram of the condensation of two beta glucose molecules here: Draw a diagram of amylose and amylopectin molecules here:

25 Doesn’t easily diffuse or affect wp gradients and osmosis Very compact – a lot can be fitted into a small area Can be quickly hydrolysed to form one of the reactants for respiration when required. Stored for use when needed (when rate of photosynthesis is low / respiration high) manysidic alpha energy

26 Subunit structure of glycogen VERY similar to amylopectin – but shorter and more highly branched

27 Glycogen Starch is never found in animal cells; instead you find glycogen (energy storage) Similar to amylopectin in starch, except shorter chain and it’s more highly branched Stored as small granules mainly in the muscles and liver. Consists of 1-4 glycosidic linked chains of alpha glucose which are shorter and more branching Not soluble in water Readily hydrolysed What are the advantages of these properties?

28 Starch Glycogen Cellulose Alpha and Beta Glucose Condensation and Hydrolysis Amylose: Made up of _______ glyco_____ chains of _____glucose Amylopectin: Made up of _____ glucose and is branched (1,4 glycosidic bonds) Main role of starch is _______storage, something it’s especially suited for because: FEATUREWhy this is useful It is insoluble Helical shape When hydrolysed it forms α- glucose Stored as granules Glycogen: Made up of very short chains of _____ glucose and is highly branched (1,4 glycosidic bonds) Stored as small granules mainly in the muscles and liver. Readily hydrolysed. Why is this helpful? …………………………………………………………………………………………………………. Draw a diagram of a glycogen molecule here: Forms straight unbranched chains rather a coiled chain like starch or a branched chain like glycogen. Chains run parallel to each other allowing hydrogen bonds to form cross- links between adjacent chains (microfibrils) Provides strength to cellulose cell walls Individual bonds are weak but large numbers adds to considerable strength. Draw a diagram of the condensation of two beta glucose molecules here: Draw a diagram of amylose and amylopectin molecules here:

29 TASK Answer the question on glycogen on your sheet. Finished? Draw a molecule of glycogen and start to research cellulose. 29

30 alpha So that glycogen can be stored for occasions when respiration is high and energy is needed in the future, when supplies of glucose are scarce.

31 Carbohydrate polymers POLYSACCHRIDES Starch (amylose and amylopectin) Glycogen (shorter amylose chains with more branching Cellulose (beta-glucose)

32 β-glucose polymers β-glucose molecules bond together through condensation reaction to form long chain Unlike α-glucose, forms long straight chains due to orientation of glycosidic bonds Straight chains contain up to 10 000 β-glucose molecules Cellulose chains found only in plants

33 Orientation of β-glucose and chain formation Made of β-glucose rather than α-glucose like in starch and glycogen. ‘flip-flop’ arrangement of glucose

34 Cellulose Forms straight unbranched chains rather than a coiled chain like starch or a branched chain like glycogen. Chains run parallel to each other allowing hydrogen bonds to form cross-links between adjacent chains (microfibrils) Provides strength to cellulose cell walls Individual bonds are weak but large numbers adds to considerable strength.

35 Cellulose chains, microfibrils and macrofibril (fibre)‏

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37 Starch Glycogen Cellulose Alpha and Beta Glucose Condensation and Hydrolysis Amylose: Made up of _______ glyco_____ chains of _____glucose Amylopectin: Made up of _____ glucose and is branched (1,4 glycosidic bonds) Main role of starch is _______storage, something it’s especially suited for because: FEATUREWhy this is useful It is insoluble Helical shape When hydrolysed it forms α- glucose Stored as granules Glycogen: Made up of very short chains of _____ glucose and is highly branched (1,4 glycosidic bonds) Stored as small granules mainly in the muscles and liver. Readily hydrolysed. Why is this helpful? …………………………………………………………………………………………………………. Draw a diagram of a glycogen molecule here: Forms straight unbranched chains rather a coiled chain like starch or a branched chain like glycogen. Chains run parallel to each other allowing hydrogen bonds to form cross- links between adjacent chains (microfibrils) Provides strength to cellulose cell walls Individual bonds are weak but large numbers adds to considerable strength. Draw a diagram of the condensation of two beta glucose molecules here: Draw a diagram of amylose and amylopectin molecules here:

38 TASK Draw the condensation of two beta glucose molecules to form cellulose on your sheet. Finished? Pick up a set of past paper questions from the side bench and start to make your way through them. 38

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41 Task Construct a table to compare starch, glycogen and cellulose. Think about their structures, properties and functions. 41

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50 Starch, glycogen and cellulose Aims: How are α-glucose monomers arranged to form the polymers of starch and glycogen? How are β-glucose monomer arranged to form the polymer cellulose? How do the molecular structures of starch, glycogen and cellulose relate to their functions? Plenary: Compare and contrast starch, glycogen and cellulose


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