![Question
1. Compare and contrast the structures
of starch, glycogen and cellulose,
showing how each molecule’s
structure is linked to its function.
[10 marks]](https://image.slidesharecdn.com/2-cellulose-starch-230116193913-da29e3e3/85/2-Cellulose-Starch-ppt-20-320.jpg)
![Mark Scheme
[1] Gycogen is a chain of α-glucose molecules
[2] Cellulose – chain of β-glucose molecules
[3] Glycogen’s chain is compact but very branched, whereas
[4] Cellulose’s chain is very long, straight and unbranched
[5] and these chains in cellulose are bonded to form fibres
[6] Glycogen’s structure makes it a good food store in
animals
[7] The branches allow enzymes to access the glycosidic
bonds
[8] to break the food store down quickly
[9] Cellulose’s structure makes it a good structure in cell
walls
[10] The fibres/ H bonds provide strength](https://image.slidesharecdn.com/2-cellulose-starch-230116193913-da29e3e3/85/2-Cellulose-Starch-ppt-21-320.jpg)
2--Cellulose---Starch.ppt
- 1. Carbohydrates Recap Can you: • Name 3 monosaccharides • Name 3 disaccharides and which monomers they are made from • Draw the difference between α and β glucose • Draw the reaction which results in two monosaccharides joining together • Recall 3 polysaccharides (and their monomers)
- 2. Two forms of glucose
- 4. Starch, glycogen and cellulose 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?
- 5. Carbohydrate polymers POLYSACCHRIDES • Starch (amylose and amylopectin) • Glycogen (shorter amylose chains with more branching • Cellulose (beta-glucose)
- 6. Cellulose Beta-glucose molecules bond together through condensation reaction to form long chain Unlike alpha-glucose forms long straight chains due to orientation of glycosidic bonds Straight chains contain up to 10 000 beta-glucose molecules Inverted glycosidic bond
- 7. α glucose molecule β glucose molecule
- 8. 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.
- 9. • Each cellulose chain consists of 1000 to 10000 glucose units • H bonds from between OH groups of neighbouring cellulose chains • Form bundles = microfibrils • Large numbers of H bonds produce a strong structure Microfibrils
- 10. Cellulose chain, microfibrils and macrofibril (fibre)
- 11. Microfibrils
- 12. Cell Walls
- 13. Carbohydrate polymers POLYSACCHRIDES • Starch (amylose and amylopectin) • Glycogen (shorter amylose chains with more branching • Cellulose (beta-glucose)
- 14. • Amylose (α helix) – 20% of starch • Amylopectin (branched starch) – 80% Starch
- 15. Amylose 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 = amylose 1000s of glucose molecules bonded together by α1-4 glycosidic bonds in condensation reactions makes starch (amylose)
- 16. Amylopectin • Highly branched • Can be hydrolysed more quickly than amylose • α-glucose molecules joined by α1-4 glycosidic bonds with α1-6 branches every 20-30 monomers • Plants store it then hydrolyse it when they need a supply of energy
- 17. 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?
- 18. Carbohydrate polymers POLYSACCHRIDES • Starch (amylose and amylopectin) • Glycogen (shorter amylose chains with more branching) • Cellulose (beta-glucose)
- 19. Glycogen Starch is never found in animal cells instead you find glycogen (energy storage) Shorter chain and its more highly branched Stored as small granules mainly in the muscles and liver. Readily hydrolysed What are the advantages of these properties?
- 20. Question 1. Compare and contrast the structures of starch, glycogen and cellulose, showing how each molecule’s structure is linked to its function. [10 marks]
- 21. Mark Scheme [1] Gycogen is a chain of α-glucose molecules [2] Cellulose – chain of β-glucose molecules [3] Glycogen’s chain is compact but very branched, whereas [4] Cellulose’s chain is very long, straight and unbranched [5] and these chains in cellulose are bonded to form fibres [6] Glycogen’s structure makes it a good food store in animals [7] The branches allow enzymes to access the glycosidic bonds [8] to break the food store down quickly [9] Cellulose’s structure makes it a good structure in cell walls [10] The fibres/ H bonds provide strength
- 22. 22
- 23. 23
- 25. 25
- 26. • Formed of microfibrils (60-70 cellulose molecules) • Microfibrils wound into a helix around the cell and stuck with a polysaccharide glue • Successive layers of microfibrils laid down at angles to one another • Glue composed of short, branched polysaccharides = HEMICELLULOSES and PECTINS • Bind to each other and the surface of cellulose to bind them together • Pectins also component of middle lamella (between cells walls of adjacent cells) – holds the cells together
- 27. Cellulose microfibrils in matrix of hemicelluloses make cell wall VERY STRONG and VERY FLEXIBLE
Editor's Notes
- #12: Christmas rose leaf sem Buttercup stem vascular tissue Plant cell wall SEM Xylem plant cells sem