Carbohydrates

 Carbohydrates

 Carbohydrates are aldehyde or ketone derivatives of polyhydric aclcohols or any substance derived from them. 

Importance of carbohydrates :

Carbohydrates are widely distributed both in plants and in animal tissues.In plnts,

 they are produced by photosynthesis.Carbohydrate constitute about 60% of our diet .they are important for:

1. Energy production e.g. glucose.
2.  formation of structural elements in animal and plant cells.
3. formation of glycolipids (Carbohydrates combined with lipids) and glycoproteins (Carbohydrates combined with protein) both enter in the structure of cell membrance . 

Classification of carbohydrates :

• Monosaccharides : contain one sugar unit
• Disaccharides :contain two sugar units
• Oligosaccharides : contain 3-10 sugar unit
• Polysaccharides : contain more than 10 sugar unit 

Monosaccharides

* They are the simple units of carbohydrate i.e. on hydrlysis ,they can not give a simpler from The genral formula is Cn (H2O)n .

• Naming (nomenclature) of monosaccharides:

According to the presence of  aldehyde or ketone  group:

 ketoses : monosaccharides containing ketone group (- c = o)
Aldoses : monosaccharides  containing aldehyde group (- CHO).   The suffix – ose means sugar .

According to the number of carbon atoms:

• Trioses : monosaccharides  containing 3 carbons
• Tetroses : monosaccharides  containing 4 carbons
•  pentoses : monosaccharides  containing 5 carbons
• Hexoses : monosaccharides  containing 6 carbons
• Heptoses: monosaccharides  containing 7 carbons

According to both presence of aldehyde or  ketone group and number of carbon atoms :

• Aldotrioses and ketotrioses
• Aldotetroses and ketotetroses
• Aldopentoses and ketopentoses
• Aldohexoses and ketohexoses

Classification of monosaccharide :

Trioses : monosaccharide containing 3 carbons

• Aldotrioses : Glyceraldehyde  "
• ketotrioses:Dihydroxyacetone

Tetroses : monosaccharides containing 4 carbon atoms :

• Aldotetroses : Erythrose
• ketotetrose : Erythulose

pentoses : monosaccharides containing 5 carbon atoms

• Aldopentoses :Ribose , arabinose and xlyose
• Ketopentoses : Ribuose and xylulose

Hexoses :monosaccharides containing  6 carbon atoms

• Aldohexoses :glucose , mannose and galactose
• Ketohexose :fructose

Importance (functions) of pentoses :

1. Ribose and deoxyribose enter in the structure of nucleic acids RNA and DNA
2. Ribose enter in the structure of ATP, GTP and other high energy phosphate compounds
3. Ribose enter in the structure of coenzymes NAD,NADP and flavoproteins
4. Ribose phosphate and ribulose phosphate are intermediates in pentose  phosphate pathway (a minor pathway for glucose oxidation).
5. Arabinose and xylose are constituents of glycoproteins in plants and animals .
6. Lyxose is constituent of lyxoflavin isolated from human heart muscle
7. xylose is an intermediate in uronic acid pathway (a minor pathway for glucose oxidation )

Importance of Hexoses:

1. Glucose is the most important sugar in carbohydrate : Dietary carbohydrates are absorbed in the form of glucose . In the liver and other tissues glucose is converted to all carbohydrates in the body e.g. glycogen / galactose / ribose and fructose . 
2. Glucose is the major source of energy in mammals
3. Fructose fruit sugar .It can be converted into glucose in the liver + It is the main sugar of semen
4. Galactose : It can be converted in to glucose in the liver . It is synthesized in mammary gland to make the lactose of milk (milk sugar)
5. Mannose : A constituent of many glycoproteins
6. Heptoses : As sedoheptulose (which is formed in the course of glucose oxidation (pentose phosphate pathway).