Comparing and contrasting functions and features of carbohydrates cellulose, chitin,starch and glycogen - page 3
Keywords: carbohydrates structure function features starch chitin cellulose glycogen essay
By xbryonyx on 13/02/2007
Level: A Level (Year 12) / AS Level
Page Number: 3 of 4 pages: 1 2 3 4
polymer increased strength. Chitin is also closely related chemically to cellulose, in that it is a long unbranched chain of glucose derivatives. Both materials contribute structure and strength, protecting the organism.(2)
Starch is a complex carbohydrate which is insoluble in water; it is used by plants as a way to store excess glucose The primary function of starch in plants, is to act as an energy storage molecule for the organism. In plants simple sugars are linked into starch molecules by specialized cellular organs called amyloplasts.(2)
Glycogen, however is used in the animal body. It’s most apparent function is in the liver where it is formed from glucose in the bloodstream and is stored in the liver. The conversion of glucose to glycogen (glycogenesis) and hydrolysis of glycogen to glucose (glycogenolysis) together are the usual mechanism for maintenance of normal levels of blood sugar. During glycogenesis the rising blood glucose levels cause the pancreas to secrete insulin. Glucose from the portal vein then enters the liver cells (hepatocytes). Insulin acts on the hepatocytes to stimulate the action of several enzymes, including glycogen synthase.(2) Glucose molecules are added to the chains of glycogen as long as both insulin and glucose remain plentiful. In the case of glycogenolysis falling glucose levels lead to a reducttion in insulin production and glycogen synthesis stops. About four hours after a meal, glycogen begins to be broken down to be converted again to glucose. Glycogen phosphorylase is the primary enzyme of glycogen breakdown. (2) For the next 8–12 hours, glucose obtained from liver glycogen will be the primary source of blood glucose to be used by the rest of the body. Another function of glycogen is in muscle cells as an immediate reserve source of available glucose for muscle cells, other cells that contain small amounts use it locally as well. Muscle cells lack the ability to pass glucose into the blood, so the glycogen they store internally is destined for internal use and is not shared with other cells, unlike liver cells.(2)
Cellulose links to starch as its function also occurs in plants, being the main component of cell walls.In combination with lignin and hemicellulose, it is found in all plant material. Cellulose is the most abundant form of living terrestrial biomass.(3)
Although its function is in the animal body, as is glycogen’s,chitin can be compared to cellulose, in that it contributes strength and protection to the organism. In
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