23. Describe the structure of starch and
how the structure is adapted to its function.
Answer:
Starch
-a polysaccharide
-not soluble
in water
-not sweet to
taste
-major storage
form of carbohydrate in plants
-made up from
alpha-glucose
-Molecular
formula (C6H10O5)n
-polymer as a
result of polymerization from glucose bond together by glycosidic bond
-made up of
two components, amylose and amylopectin
Amylose
-a linear
unbranched polymer of 200 to 1500 alpha-glucose units in a repeating sequence
of α-1,4-glycosidic linkages.
-In water, it
forms helix due to hydrogen bond between hydroxyl group and form a more compact
shape
11.jpg)
Amylose
Amylopectin
-a branched
polymer of 2000 to200000 alpha-glucose units per starch molecule
-linked by α-1, 4-glycosidic bonds, but the
chains are shorter than in amylose and there are side-branches.
-the branches are formed by α-1, 6-glycosidic bond
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*The amylose helices are entangled in
the branches of amylopectin to form a complex, compact, three dimensional
starch molecules
*Starch is insoluble
in water. It can be stored in large amounts with little effect on the water
potential of plant cells and does not affect the cellular metabolic activities.
*Mixture of
amylose and amylopectin molecules build up into large starch grains which are commonly
found in chloroplast, potato tubers, cereals and legumes
*Starch is
never found in animal cells.
-It is a
compact molecules that could save a lot of spaces
-unable to
diffuse out of its storage space
-doesn’t dissolve in water n thus
could be stored in cell without changing the osmotic pressure of the cell
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