Starch glycogen and cellulose On the mini whiteboard

Starch, glycogen and cellulose

On the mini whiteboard… 1. Draw a molecule of α-glucose. 2. What disaccharide is formed when 2 αglucose molecules react? 3. What type of bond is formed between the molecules? 4. What type of reaction is this? 5. Which enzyme breaks down maltose? 6. What other substance is needed? 7. What type of reaction is this? 8. What are the two molecules that make up starch?

Condensation and hydrolysis

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

Starch: Amylose and. Amylopectin 5

Starch: Amylose and Amylopectin 6

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 What are the advantages of these properties?

Glycogen • Starch is never found in animal cells; instead you find glycogen. • Similar to amylopectin in starch, except shorter chain and more highly branched (1 -4 and 1 -6 glycosidic linked chains of α-glucose). • Stored as small granules mainly in muscles and liver. • Not soluble in water. • Readily hydrolysed. What are the advantages of these properties?

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

Two forms of glucose

Beta glucose polymers n β-glucose molecules bond together through condensation reaction to form long chains. n Unlike α-glucose, forms long straight chains due to orientation of glycosidic bonds. n Straight chains contain up to 10 000 βglucose molecules. n Cellulose chains found only in plants – where?

Orientation of beta-glucose and chain formation ‘Flip-flop’ arrangement of molecules.

Cellulose n Forms straight, unbranched chains. n Chains run parallel to each other allowing H-bonds to form cross-links between adjacent chains (microfibrils). n Provides strength to cellulose cell walls. n Individual bonds are weak but large numbers adds to considerable strength.

Cellulose chain, microfibrils and macrofibril (fibre)

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Carbohydrate polymers: POLYSACCHARIDES • Starch (amylose and amylopectin) • Glycogen (shorter amylopectin-type chains with more branching) • Cellulose (beta-glucose) COMPLETE THE COMPARISON SHEET.

Write G, S or C on your whiteboard… Which one: - is made of β-glucose? - is stored inside plant cells? - has the most branches? - contains amylose and amylopectin? - may be found in the liver? - enables trees to grow tall? 18

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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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