Introduction of Carbohydrates in Biochemistry | Classification of the Carbohydrates | Carbohydrates about Sugar | Medical World

Introduction of Carbohydrates

Carbohydrate are the most abundant organic molecules in nature. They are primarily composed of the elements carbon, hydrogen and oxygen. 

Carbohydrates may be defined as the polyhydroxyaldehydes or ketones or compounds which produce them on hydrolysis.

Functions of carbohydrates 

1-  they are the most abundant dietary source of energy.

2-  carbohydrates participate in the structure of cell membrane and cellular functions such as cell growth and fertilization 

3- carbohydrates also serve as the storage form of energy to meet the immediate energy demands of the body.

4-  carbohydrates are precursors for many organic compounds.

Classification of the Carbohydrates

They are broadly classified into three major groups-

1- monosaccharides

2- oligosaccharide 

3-  polysaccharide 

Monosaccharide

Monosaccharide are the simplest group of carbohydrate and are often referred to as simple sugars. The monosaccharide are divided into different categories- 

Aldehyde - when the functional group in monosaccharide is an aldehyde, they are known as aldoses . 

 For example :  glucose 

Ketoses -  when the functional group is a keto group, they are referred to as ketoses .

For example :  fructose 

 Oligosaccharides Definition and examples

Oligosaccharide contain 2-10 monosaccharide molecules which are liberated on hydrolysis. 

Oligosaccharide consists of disaccharide 

 disaccharide definition in medical

Disaccharide consists of two monosaccharide units held together by glycosidic bond. The disaccharide are of two types-

1- Reducing disaccharide with free aldehyde or keto group e.g. maltose 

Maltose 

Maltose is composed of two alpha-D-glucose units held together by alpha (1-4) glycosidic bond. 

2- Non-reducing disaccharide with no free aldehyde or keto group e.g. sucrose 

Sucrose 

Sucrose is the sugar of commerce mostly produced by sugar cane and sugar beets. Sucrose is made up of alpha-D-glucose and beta-D-fructose.

 Describe about Polysaccharide

Polysaccharide  consists of repeat units of monosaccharide or their derivatives, held together by glycosidic bonds. Polysaccharide are linear as well as branched polymers. 

Polysaccharides and its types

Polysaccharide are of two types 

1- Homopolysaccharides

2- Hetropolysaccharides 

Homopolysaccharides - they are the single type of monosaccharide. It consists of following types- 

A). Starch -  starch is the carbohydrate reserve of plants which is the most important dietary source for higher animals, including man . Starch is a homopolymer composed of D-glucose units held by alpha-glycosidic bonds. It is known as glucose or glucan.

Starch consists of two polysaccharide components-water soluble amylase and a water insoluble amylopectin. 

B) Dextrins -  dextrins are the breakdown products of starch by the enzyme amylase or dilute acids. 

C) Inulin- inulin is a polymer of fructose. It occurs in garlic, onion etc

D) Glycogen-  glycogen is the carbohydrate reserve in animals, hence often referred to as animal starch. It is present in high concentration in liver, followed by muscles, brain etc

E) Cellulose- cellulose occurs exclusively in plants and it is the most abundant organic substance in plant kingdom.

Heteropolysaccharide definition

Hetropolysaccharide - when the polysaccharide are composed of different types of sugar or their derivatives, they are referred to as hetropolysaccharide or hetroglycans.

Mucopolysaccharide 

Mucopolysaccharide are hetroglycans made up of repeating units of sugar derivatives, namely amino sugar and ironic acids. These are more commonly known as glycosaminoglycans (GAG) .

The important mucopolysaccharide includes hyaluronic acid, chondroitin 4-sulphates, heparin , dermatan sulphate and keratin sulphate 

A) Hyaluronic acid -  they are important GAG found in the ground substance of synovial fluid and vitreous humour of eyes. It is also present as ground substance in connective tissues, and forms a gel around the ovum. Hyaluronic acid serves as a lubricant and shock absorand in joints. 

B) Chondroitin sulfates- it is a major constituents of various mammalian tissues like as bone, cartilage, tendons, heart , Alves, skin, cornea etc.

C) Heparin- it is an anticoagulant that occurs in blood, lungs, liver, kidney, spleen etc. heparin helps in the release of the enzymes lipoprotein lipase which help the turbidity of lipemic plasma.

D). Dermatan sulfate -  dermatan sulfate is derived from the fact that this compound mostly occurs in the skin.

E) Keratin sulfate -  it is a heterogeneous GAG with a variable sulfate content besides small amounts of mannose, fructose, silica acid etc.

Glycoprotein 

Several proteins are covalently bound to carbohydrates which are referred to as glycoproteins . The carbohydrate content of glycoprotein various from 1% to 90% by weight. Glycoprotein found in collagen , ceruloplasmin immunoglobulins, synovial glycoproteins.