Monosaccharides Disaccharides and Polysaccharides
The Role of Disaccharides:
Maltose :
Maltose is a disaccharide found in fruits and also found in our digestive tract as a result of the breakdown product during the digestion of starch by an enzyme called amylase. It is also brewing industries to synthesize alcohol.
Lactose:
Lactose is milk sugar and it is an important energy source for young mammals. The sucrose or cane sugar is the most abundant disaccharide in nature and is hydrolyzed into glucose and fructose. It is obtained commercially from sugar cane or sugar beet, the sugar we normally buy in shops.
All monosaccharides and some disaccharides including maltose and lactose are reducing sugars because these sugars can carry out a type of chemical reaction known as reduction. Sucrose is the most common non-reducing sugar.
Polysaccharides:
Polysaccharides exhibit the following properties. They are made up of several
monosaccharides, linked by glycosidic linkage may be branched or unbranched. They are tasteless and insoluble or sometimes sparingly soluble in water. They are most abundant in nature. Their general formula is C,(H, O),.
Types of polysaccharides:
Important polysaccharides are starch, glycogen, cellulose, dextrin, agar, chitin, and pectin. All the above polysaccharides function chiefly as food, energy storage, and
structural material.
Starch:
Starch is the polymer of glucose. It is a fuel stored in plants and the main source of food for animals. There are two types of starches, the simplest form is amylose, which has a straight chain structure and is joined by 1-4 glycosidic linkage. The other form is amylopectin which is a more complex and branched polymer with 1-6 linkage at the branched point.
Amylose is soluble in warm water but insoluble in cold water due to its simple structure while amylopectin is neither soluble in warm nor in cold water.
Cellulose:
It is a polymer of glucose and the most abundant carbohydrate in nature, unlike starch and glycogen it has a structural role and main constituent of the cell walls of plants and has cellulase enzyme. However, herbivores can digest it because their digestive tract is algae.
Cellulose is highly insoluble in water and we can not digest it because we do not contain microorganisms like bacteria, yeast, or protozoans which secrete cellulase enzymes.
Glycogen:
It is a polymer of glucose and is also called animal starch. It is stored in the liver and muscles. It is also found in fungi. It is insoluble in water due to its complex structure and
converted back to glucose monomer when needed.
Chitin:
It is the structural nitrogenous polysaccharide and closely related to cellulose, found in the cell walls of fungi and the exoskeleton of arthropods.
2.4 Proteins
Proteins are polymers of amino acids and they are the most abundant organic substances in the cell. All proteins must contain C, H, O, and N, some may also contain, P and S while few have Fe, I, Mg, etc.
Amino Acids:
These are the building blocks of proteins. There are about 170 different types of amino acids discovered in cells and tissues, out of these 25 are involved in protein synthesis. Most proteins, however, are made up of 20 types of amino acids. Each amino acid consists of an alpha carbon.
On one side of this alpha carbon NH, (amino group) is present while on the other side, COOH (Carboxylic acid group) is present. On the third side, Hydrogen is present while fourth side radical group is attached which is different in all amino
acids.
Many amino acids are nonessential because the body of the organisms can synthesize them, they are mostly not required as dietary food. A few amino acids are essential because they are required in diet.
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