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Discuss how the molecular structure of starch, glycogen and cellulose relate to their functions in living organisms. Polysaccharides Difference between Starch, Glycogen and Cellulose Starch Glycogen Cellulose Monomer...

Discuss how the molecular structure of starch, glycogen and cellulose relate to their functions in living organisms. Polysaccharides Difference between Starch, Glycogen and Cellulose Starch Glycogen Cellulose Monomer α – glucose α – glucose β – glucose Type of bond between 1,4 glycosidic bond 1,4 and 1,6 glycosidic 1,4 glycosidic bond monomers (amylose) bonds 1,4 and 1,6 glycosidic bond (amylopectin) Nature of chain Amylose is coiled, Short, many branched Straight, long unbranched chains, some coiling unbranched chains for Amylopectin is long, H-bonds, with branched chains, adjacent chains some coiling Function Carbohydrate energy Carbohydrate energy Structural component source in plants source in animals and in plant cell walls fungi Starch Starch is a polysaccharide that is made up of α – glucose molecules. It occurs in plants and is found in starch grains. Strach is composed of amylose and amylopectin. Amylose is surrounded by amylopectin which is insoluble in water. Amylose The carbohydrate amylose consists of repeating units of α-glucose molecules with 1,4 glycosidic bonds (approximately 200-1500 glucose units). Amylose makes up 20-30% of the starch molecule and is unbranched. Its OH groups participate in bonding and are located on one side of the chain which causes them to attract to each other and as a result, causing coiling of amylose. Amylose coils in a helix which makes it more compact and insoluble in water. It can be easily hydrolysed to produce glucose when can then be used in the process of respiration. Starch is ideal for energy storage and does not affect the water potential in cells. Amylopectin This is a branched molecule produced by both alpha 1,4 glycosidic bonds and alpha 1,6 glycosidic bonds. It consists of 2000 to 200000 glucose units per molecule. At every 20 glucose units, a branch occurs due to a 1,6 glycosidic bond. Amylopectin has a brush-like shape and is able to also wind into a loose helix shape. Since it has many glucose units, in many branches, a large amount can be hydrolysed at the same time, making it easier for glucose to be available for respiration. It is also insoluble, unreactive and does not affect the water potential of the cell. Glycogen Glycogen is the energy storage molecule for animals. It is a polysaccharide that consists of alpha glucose units that are bonded via alpha 1,4 and 1,6 glycosidic bonds. Glycogen is very similar to the structure of amylopectin however, it is more highly branched, and the chains are shorter. The increase in the branching structure means it is broken down faster by amylase to give glucose at a faster rate since animals are more active than plants. Glycogen granules are smaller than starch grains, and so more of them can fit in a given space. A red-violet colour will be observed when iodine is added to glycogen. Cellulose Cellulose is the most abundant organic molecule on each. It us a structural polysaccharide, unlike starch and glycogen. It has extended chains which form fibers. As opposed to amylose, amylopectin and glycogen, cellulose is made up for beta glucose units. This change means that for the formation for the 1,4 glycosidic bonds, each successive unit of glucose is rotated 180 degrees (flipped). This allows for the OH groups to project out on both sides of the chain. As a result, hydrogen bonding occurs which present the coiling structure observed in starch and glycogen. Approximately 60 of these chains are held together to form a cellulose microfibril which have high tensile strength due to the large number of hydrogen bonds within a single chain and among other chains as well. Microfibrils are made up of pectins and hemicelluloses in the plant cell wall. It is non-living and fully permeable and surrounds the plants cells to provide structural support. Due to its resistance against pulling forces and high tensile strength, it prevents cells from rupturing when water enters via osmosis so they can be turgid.