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Senin, 20 Mei 2013

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


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