Starch, glycogen and cellulose

1. Draw a molecule of -glucose.2. What disaccharide is formed when 2 -glucose 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?On the mini whiteboard

Condensation and hydrolysis

StarchFound in many parts of the plant as small grains.Large amounts in seeds and storage organs.Major energy source in most diets.

1000s of -glucose molecules bonded together by glycosidic bonds in condensation reactions makes starch.

Starch: Amylose andAmylopectin*

Starch: Amylose and Amylopectin*

StarchMain role of starch is energy storage, something its especially suited for because:

It is insolubleIt is compactWhen hydrolysed it forms -glucose

What are the advantages of these properties?

GlycogenStarch 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 -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 glycogenVERY similar to amylopectin but shorter and more highly branched

Two forms of glucose

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

Orientation of beta-glucose and chain formationFlip-flop arrangement of molecules.

CelluloseForms straight, unbranched chains.Chains run parallel to each other allowing H-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.

Cellulose chain, microfibrils and macrofibril (fibre)

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Carbohydrate polymers:POLYSACCHARIDESStarch (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 whiteboardWhich one:- is made of -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?

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Starch, glycogen and celluloseAims:How are -glucose monomers arranged to form the polymers of starch and glycogen?How are -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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