Starch
Starch: structure
- Starch is the storage polysaccharide of plants
- It is stored as granules in plastids (e.g. chloroplasts) and amyloplasts (small, membrane-bound organelles containing starch granules)
- Due to starch molecules being large polymers consisting of thousands of glucose monomers, starch takes longer to digest than glucose
- Starch is constructed from two different polysaccharides:
- Amylose (10 - 30% of starch)
- Unbranched helix-shaped chain with 1,4 glycosidic bonds between α-glucose molecules
- The helix shape enables it to be more compact and thus it is more resistant to digestion
- Amylose (10 - 30% of starch)
Amylose - one of the two polysaccharides present in starch
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- Amylopectin (70 - 90% of starch)
- 1,4 glycosidic bonds between α-glucose molecules (as found in amylose) but also 1,6 glycosidic bonds form between glucose molecules creating a branched molecule
- The branches result in many terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added to for storage
- Amylopectin (70 - 90% of starch)
Amylopectin - the other polysaccharide present in starch
Starch: function
- Starch is a storage polysaccharide because it is:
- Compact (so large quantities can be stored)
- Insoluble (so will have no osmotic effect, unlike glucose which would cause water to move into cells, meaning cells would then have to have thicker cell walls to withstand the increased internal water pressure)