Carbohydrates

The literally means of carbohydrate is hydrated carbon. It is made of carbon, hydrogen and oxygen. The ratio of hydrogen and oxygen is same as in water. Chemically carbohydrate can be defined as the polyhydroxy aldehyde or ketones, complex substance which on hydrolysis yield polyhydoxy aldehyde or ketone subunits. It general formula is Cn(H2O)n where n is whole number from 3 to many.

Hydrolysis:   

           "The break down of large molecules into small by utilizing water molecules".

Occurrence and Source of carbohydrate:

They are found in all organisms and almost all parts of cells. It occur abundantly in organisms. Green plants are main source of carbohydrate. It is first product of photosynthesis. Other compounds of plants are produced from carbohydrate by different chemical reactions.

Functions:

1: Carbohydrates play both structural and functional roles.
2: Simple carbohydrates like glucose, are the main source of energy in cells.
3:Some carbohydrate like cellulose, are the main component of cell walls in plants and micro-organisms.
4: Carbohydrate in cells combine with protein and lipids  to form glycoprotien and  glycolipid  respectively. They have structural role in extracellular matrix of animals and bacteria cell wall. Both these conjugate molecules are components of cell membrane. 

Classification of Carbohydrate:  

Carbohydrate also called saccharides means sugar and are classified into three groups.

1: Monosaccharide

2: Oligosaccharide

3: Polysaccharide 

Monosaccharide:

1: These are sweet in test.

2: These are simple sugar.

3: They are easily soluble in water, and cannot be hydrolyzed into simple sugar. 

4: Chemically they are either polyhydroxy aldehyde or ketone. All carbon atoms in a monosaccharide except one, have a hydroxyl group. The remaining carbon atom is either apart of an aldeyde group or a keto group. The sugar with aldehyde group is called aldo-sugar and with the keton group is called keto-sugar.

4: Classification of Monosaccharides: In nature Monosaccharides with 3 to 7 carbon atoms are found. They are called trioses (3C),tetroses (4C), pentoses (5C), hexoses (6C), heptoses (7C). They have general formula (CH2O).

5: Glysaccharide and Dihydroxyacetone, both trioses (C3H6O3) are intermediates in respiration and photosynthesis. Tetroses are rare in nature occur in some bacteria. Pentoses and hexoses are most common. From the biological point of view the most important hexsose is glucose. It is an aldo sugar.

6:Most of the mono saccharides form a ring structure when in solution. eg, ribose  form five cornered structure called ribofuranose and glucose form sis sided structure called gtycopyranose.
7:in free state glucose is present in all fruits but being abudntant in grapes, dates and figs. Our blood cotains 0.08% glucose. in combine form it found in many disaccharides and polysaccharides. Glucose naturally produced in green plants which take carbon dioxide from air and water from the soil to synthesize glucose. Energy consumed in this process which is provided by sunlight. This process is called photosynthesis.
  

Oligosaccharide:

1: These are comparativly less sweet in test.

2: They are less soluble in water.

3: On hydrolysis oligosaccharides yield from tow to ten monosaccharides. The ones yielding two monosaccharides are known as disaccharides. Those yielding three monosaccharides are known as trisaccharides and so on. The covalent bond between two monosaccharides is called Glycosidic bond C-O.
4: Phsiologically important disaccharides are maltose, sucrose and lactose. Most familiar
 disaccharides is sucrose (cane sugar) which on hydrolysis yields glucose and fructose, both of which are reducing sugar. Its formula is

C12H22O11.

Polysaccharide: 

 1: These are the most complex and most abundant carbohydrate in nature.
2: They are test less and usually branched.
3: They are formed by several mono saccharide units linked by glycosidic bonds.
4: They are sparingly soluble n water.
5: They have high molecular weight. i.g, strach,glycogen, cellulose, dextrins, agar, pectin and chitin etc.

Strach:

 1: It is found in fruits, grains, seeds and tubers.

2: It is main source of carbohydrates for animals.

3: On hydrolysis it yields glucose molecule.

4: Give blue color with Iodine .

Types:

There are two types of strach.

Amylose: Have unbranched chains of glucose. It is soluble in hot water.  

Amylopectin:  Have branched chains and are in soluble in hot or cold water.

Glycogen: 

1: It is also called animal strach.
2: It is the chief form of carbohydrate stored in animals body.
3: It is abundantly found in liver and muscles through in all animals cells.
4: It is insoluble in water, and gives red color with iodine 
5: On hydrolysis it also yields glucose molecule.

Cellulose:  

1: It is most abundant carbohydrate in nature. 
2: Cotton is the pure form of cellulose. 
3: It is the main component of cell wall of plants. 
4: It is highly insoluble in water.  
5: On hydrolysis it also yields glucose molecule. 
6: It is not digested in human digestive track. In herbivores it is digested because of micro-organisms in their digestive track. These micro-organisms secrete an enzyme called cellulase for digestion. Cellulose give no color with iodine.