These chains of α-glucose coil to form spirals and these are held in place by hydrogen bonds.
Amylopectin, on the other hand, is a branched chain due to some of its glucose residues joining via a 1,6 glycosidic bond, however this is still formed by a condensation reaction.
Due to starch being made up from amylose and amylopectin which are both polysaccharides and produced by a condensation reaction, starch can easily be broken down when H20 is added and the –o- glycosidic bond is broken, this process is called hydrolysis. The breaking of this bond has a result of 2 α-glucose molecules…it’s the opposite reaction of condensation. Now being in the form of glucose it can be used in respiration by the plant.
Also due to amylose and amylopectin both being of a compact nature, it being a characteristic of the two, a large amount of starch can be stored in a relatively small space. Not only that but starch is also insoluble and therefore it won’t affect water potential (ψ) in the cells in which it’s stored, therefore it won’t cause water movement across membranes and so will stay within 1 part of a plant.
All these factors contribute to starch being an effective storage compound in plants;
-
It’s easily broken down into α-glucose molecules so can be used when needed and obtained quickly.
- It doesn’t take up large amounts of space.
- It doesn’t affect water movement across membranes and so doesn’t affect other processes within a plant!
Glycogen is also a complex carbohydrate and is the main storage of glucose in humans, it can be found in liver and muscle tissue.
This polysaccharide is similar to that of amylopectin (found in starch) however it’s even more branched, it’s similar as it too is caused by a condensation reaction and so is easily breakable by hydrolysis. The adding of H20 brings about the breaking of the –o- glycosidic bond and the production of α-glucose molecules which can then be used by the human body if needed when performing strenuous exercise.
The fact that glycogen can easily be broken down is why it’s an efficient storage compound in humans; it allows glucose to be readily available.
Cellulose is also a complex polysaccharide consisting of over 3000 or more β-glucose molecules. It’s the basic structural component of cell walls and it comprises roughly 33% of all vegetable matter and is the most abundant naturally occurring organic compound. It’s a naturally occurring polymer made up from β-glucose monomer units, these link together to form long unbranched chains. Therefore these chains (micro fibrils) can lie parallel to each other allowing hydrogen bonds to form along the chain and in doing so, ‘binding’ the chains together to form strong fibrils. These then ‘glue’ together to form the cell wall, this is of a cross hatch pattern as the fibrils lie in all directions, this also adds to the strength of cellulose. Not only that but the cross hatch structure helps adds high tensile structure to cellulose allowing it to withstand high pressure/pulling forces without breaking, therefore giving the plant cell wall its structure and strength.
Cellulose is formed when many β-glucose monomers bond together, this is a condensation reaction i.e. when bonds are made and H20 is produced. However due to the positioning of the hydroxyl group (alcohol) on each glucose monomer the pattern in cellulose is that of the glucose unit being ‘flipped over’ when compared to the glucose prior to itself in order for the OH groups to be in the correct position for a 1,4 glycosidic bond to form. This in turn allows two hydrogen atoms to be side by side and as a result a strong hydrogen bond is formed, adding to the structure of cellulose.
+ +…
β-glucose β-glucose
= + H20
Cellulose
Cellulose is an efficient structural compound due to;
- It being insoluble, so will stay rigid even when wet.
- It’s very strong so can withstand opposing forces.
Overall starch, glycogen and cellulose are efficient at their jobs, whether it’s storage or structural, for several reasons all of which have hopefully been successfully highlighted throughout this essay.
