CARBOHYDRATES

Carbohydrates are organic compounds containing carbon hydrogen and oxygen, usually in the proportion 1:2:1 respectively. Carbohidrates are divide into 4 groups monosaccharides, disaccharides, oligosaccharides and polisaccharides.

MONOSACCHARIDES

a.       Monosacccharides are the simply sugar units (monomers) which make up all other carbohydrates. They cannot be broken into smaller molecules by hydorilysis.

b.      The empirical formula is (CH₂O)_n where n = 3-7

c.       Monsaccharides are sweet, soluble in water, cam be crystallised and are called reducing sugar.

d.      Monosaccharides are characterised by the number of carbon atoms in the molecules.

      a.       Trioses (3C sugars) exm glyceraldehyde, dihidroxyacerone

      b.      Pentoses (5C sugars) exm ribulose, ribose

      c.       Hexoses (6C sugars) exm glucose, fructose, galactose, mannose

The monosaccharides molecule contains a carbonyl group. The remaining carbon atoms that do not have a carbonyl group will have hydroxyl groups.

Monosaccharides that contain aldehyde group are called aldose such as                                         glyceraldehyde,ribose,glucose and galactose. Those with keto group are called ketoses like                 dihydroxyacetone, ribulose, and fructose. In generall, aldoses are more common than ketoses.

Example of monosaccharides is glucose, the straight chain formula of glucose called an aldohexose. The self reaction in which the liniear chain of glucose bends, the hydroxyl group attached to carbon atom 5 forming a more stable ring shaped molecule. A glucose molecule is commonly shown in the form of flat ring.

DISACCHARIDES

a.       Disaccharides are formed by the condensation reaction between two monosaccharides.
       The bond linking   the monosaccharides is known as a glycosidic bond.

 Table 1. shows three disaccharides and their functions.

Disaccharides	Monomers	Source and function
Maltose (malt sugar)	Glucose + Glucose	Malt sugar in germinating barley grains Respiratory substrate
Sucrose (cane sugar)	Glucose + fructose	Sugar cane and beetroot Main form that tansported in plants
Lactose (Milk sugar)	Glucose + Galactose	Sugar found in the milk of mamals Souce of energy

OLIGOSACCHARIDES

Monosaccharides maybe linked together to form small chains called oligosaccharides. Each oligosaccharides may contain 3 – 14 monosaccharides. Oligosaccharides can be found attached to protein and lipids forming glycoprotein and glycolipids of the plasma membrane.

POLYSACCHARIDES

Polisaccharides are polymers made up of the condensation of hundreds of monosaccharides monomers. The process called polymerisation. The long chains of monosaccharides molecules are linked together by glycosidic bonds and the chains  may be branched or unbranched. Polisaccharides are generally not soluble in water and not sweet in taste.

For example is glycogen, glycogen is the major storage forms of carbohydrates in animals. It is mostly present in liver and muscle cell where high metabolism take place. Glycogen is insoluble in water and has no effect on the water potential of cellular fluid. When energy is needed and glucose concentration is low in the body, the highly branched glycogen can be hidrolysed rapidly by enzim.

Summary about carbohydrates

	Group of carbohydrates	Name of carbohydrates	Functions
Monosaccharides	Trioses C3H6O3	Glyceraldehyde	Intermediate substance in respiration and photosynthesis
		Dihydroxyaceton	Intermediate substance in respiration
	Pentose C5H10O5	Ribose	Constituen of RNA,NAD,FAD,coenzym A,ATP,AMP
		Deoxyribose	Constituen of DNA
		Ribulose	CO 2 acceptor in photoshynthesis
	Hexoses C6H12O6	Glucose	Most common respiratory substrate
		Fructose	Constituen of nectar
		Galactose	Constituen of lactose
Disaccharide C12H22O11		Maltose	Found in germinating seed such as  germinating barley, germinating mango
		Sucrose	Transport sugar in plants, stored as sugar cane and sugar cane
		Lactose	Milk Sugar
Oligosaccharides		Contains from 3 till 14 monosaccharides	Oligosaccharides are attached to intgral membrane proteins and lipids to form glycoprotein and glycolipids. They are important in cell recognition
Polysaccharides		Starch Glycogen Cellulose	Storage carbohydrates in plants Storage carbohydrates in animals Structural support to plants cell wall