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

3. Condensation and hydrolysis

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