BIOLOGICAL ROLE OF CARBOHYDRATES
By:
Sumit Sharma
Assistant proffesor in Biotechnology
INtroduction:�
Carbohydrates are
- a major source of energy from our diet.
-composed of elements such as C,H and O.
-also called as saccharides,which means SUGAR
-are produced by photosynthesis in PLANTS.
- Such as glucose are synthesized in plants from CO2,h2o, and energy from the sun.
-CARBOHYDRATES sre sugars and provide energy when consumed.
-our bodies break down carbohydrates to extract energy.
-carbohydrates are classified as biomolecules.
-SIMPLE CARBOHYDRATES are reffered to as simple sugars and are often sweet to the taste.
Consumption of more sugar than is needed for energy results in conversion of these sugars to fat.
-primary function of carbohydrates to provide energy for the body.
-simple carbohydrates have one or two sugar molecules.
-complex carbohydrates have three or more sugar molecules,such as legumes,bread,rice,pasta.
I
THE carbohydrates often termed as sugar, are the “staff of life” for most organisms.on the basis of mass,they are most abundant class of biomolecules in nature.Carbohydrates are also known as saccharides since many of those are relatively small weight have sweet taste,although this is not true of those large MOlecules in both plant and animals tissues. They are indispensable for living organisms,serving as skeletal structures in plants and also in insects and crustaceans. They also occur as food reserves in the storage organ of plants and in the liver and muscle of animals.In addition they are an important source of energy required for various metabolic activities for the living organisms,the energy being derived as result of their oxidation.
IMPORTANCE OF CARBOHYDRATES
They also serve to lubricate skeletal joints,to provide adhesion between cells and to confer biological specificity on the surface of animal calls
Plants are considerably richer in carbohydrates in comparison to the animals.in fact,animal and plant tissue differ widely in the relstive abundance of the various major classes of constituent chemicals,
They act as energy source,help control blood glucose and insulin metabolism,participate in cholesterol and triglyceride metabolism,and help with fermentation.
The digestive tract begins to breakdown carbohydrates into glucose,which is used for energy upon consumption.
CLASSIFICATION OF CARBOHYDRATES
MONOSACCHARIDES-IT is a simple carbohydrate,one that one attempted hydrolysis is not cleaved to smaller carbohydrates.
DISACCHARIDES-on hydrolysis is cleaved of two monosaccharide,which may be the same or different.e.g.sucrose
OLIGOSACCHARIDE-[OLIGOS is a Greek word that means “few”] yields 3-10 monosaccharide unit on hydrolysis.e.g. raffinose
MONOSACCHARIDES[GLUCOSE]
MONOSACCHARIDES are the most basic form of carbohydrates.most organisms produce and store energy by breaking down the monosaccharides glucose and harvest the energy released.This type of glucose are classified in terms of the number of CARBON ATOMS and also the functional group attached to it.The monosaccharide which contains aldehyde is knows as aldose and those which contain a ketone group is known as ketose.
PREPARATION OF GLUCOSE
1.From sucrose[CANE SUGAR]; we get glucose and fructose in exactly equal amounts if sucrose is boiled with dilute HCL and H2SO4 In an alcoholic solution
2.FROM STARCH; when hydrolysis of starch is carried out in boiled and diluted H2SO4 at 393K under pressure,we get glucose.
3.From galactose;galactose is produced by mammals in the form of milk.lactose holds a lot of energy in its bonds and for breaking down the bonds aparts,specific enzymes are developed by off springs of mammals.
The monosaccharides may be subdivided into trioses,tetroses,pentoses,hexoses,heptoses etc... Depending upon the number of carbon they posses;and as aldoses and ketoses,depending upon whether they contain aldehyde or ketone group.The most abundant monosaccharide in nature is the 6-carbon sugar,D-glucose.
Sometimes, a distinction in naming between aldolasesand ketoses is also maintained.the suffix –oses is kept reserved for the aldolases and the suffix uloses is used for ketoses.thus,glucose is a hexose and fructose,a hexulose.However,a few ketoses are named otherwisw,such as fructose as fruits are good source of this sugar.
DISACCHARIDES
-A disaccharide[also called a double sugar]is the sugar formed when two monosaccharides[simple sugars] are joined by glycosidic linkage.like monosaccharides,disaccharides are soluble in water.the coomon examples are sucrose,lactose,and maltose.
-Disaccharides are those carbohydrates that on hydrolysis with acids or enzymes give two molecules of monosaccharides which can either be the same or different.
-Disaccharides are formed when two monosaccharides are joined together and a molecule of water is removed,a process known as dehydration reaction.For example
.Milk sugar[lactose]is made from glucose and galactose.
.sugar from sugar cane and sugar beet[sucrose] is made from glucose and fructose.
.Maltose,another notable disaccharide,is made up of two glucose molecules.
-when two monosaccharide are combined by Glycosidic linkage,a disachharide is formed.
-Therefore they yield two molecules of same or different monosaccharide on hydrolysis.
-The disaccharide just like monosaccharide are white crystalline,sweet solids.However,even though they are soluble in water,they are too large to pass through cell membranes.
-Disaccharide are those carbohydrates that on hydrolysis with acids or enzymes give two molecules of monosaccharides which can either be the same or different.
-the oxide linkage is formed after the loss of the water molecule and then the two monosaccharides are formed by that linkage.when two monosaccharide units are joined via the oxygen atom then that linkage is called a glycosidic linkage
Classification of disaccharides
There are two functionally different classes of disaccharides;
REDUCING DISACCHARIDES;in which one monosaccharide,the reducing sugar of the pair hemiacetal unit that can perform as a reducing aldehyde group,lactose,maltose and cellobiose are example of reducing disaccharides,each with one hemiacetal unit,the other occupied by glycosidic bond which prevents it from acting as reducing agent.they can be easily detected by tests…
NON REDUCING DISACCHARIDES
INwhich the compound monosaccharides bond through an acetal linkage between their anomeric centres.this results in neither monosaccharide being left with hemiacetal unit that is free to act as reducing agent.sucrose and trehalose are examples of non-reducing disaccharide because their glycosidic bond is between their respective hemiacetal carbon atoms.the reduced chemical activityof the non-reducing sugar in comparison to reducing sugars may be an advantage where stability in storfage in storage is important.
WHICH SUGAR IS NON REDUCING ?
The most common non-reducing sugar isu
-eg.sucrose anf raffinosecrose which is commonly known as ‘table sugar’.it is non-reducing because it has no OH group attached to the anomeric carbon.
-in basic aqueous solution,a non reduced by a weak oxidising agent[one that oxidises aldehydes but not alcohols,such as Tollen’s reagent]
-there is no free aldehyde or ketonic group
0LIGOSACCHARIDES; INTRODUCTION
Oligoosaccharides,any carbohydrate of from three to six units of simple sugars [monosaccharides]A large number of oligosaccharides have been prepared by partially breaking down more complex carbohydrates[polysaccharides].most of the few naturally occurring oligosaccharides are found in plants.
Oligosaccharide are carbohydrates that contain two or more than two monosaccharides [2-10units of monosaccharides]
Oligosaccharides may contain any sugar monomer,but fructooligosaccharides and oligosaccharides get absorbed in the small intestine after getting hydrolysed,for example,maltotriose.
-oligosaccharides are important group of polymeric carbohydrate found in all living organisms.
-oligosaccharides composed of [2-10] monosaccharides residues.
-oligosaccharides are the main component of prebiotic food products.
-oligosaccharides stimulate the growth of some bacteria and increase resistance to invading pathogens.
Other oligosaccharides chain coat the outside of the some animal cells and form a ‘sugar coat’ or glycocalyx.
CLASSIFICATION OF OLIGOSACCHARIDES
The classificatipn depends upon the number of sugar units they are made up of.these include the following ;
TRISACCHARIDES:these types of oligosaccharides are made up of three monosaccharides linked together.raffinose is an example of monosaccharide which is composed of glucose,galactose and fructose.
PENTASACCHARIDES:they are composed of five monosaccharides.examples include verbascose,which is composed of three units of galactose,one unit of fructose and one unit of glucose
HEXASACCHARIDES: these are made up of six sugar units.
Similarly,heptasaccharides have seven sugar units,octasaccharides have eight monosaccharides,etc..
EXAMPLE OF OLIGOSACCHARIDE IS GALACTOOLIGOSACCHARIDES-made up of galactose molecules.eg human milk oligosaccharides.they are present in breast milk.
polysaccharides
Containing 10 or more monosaccharides unit attach together
.EXAMPLES
1.STARCH-DIGESTIBLE
2.GLYCOGEN-DIGESTIBLE
3.FIBER-DIGESTIBLE
Long chains of glucose units form these polysaccharides
>cellulose gives structure to plants,fiber to our diet
>glycogen is an energy storage sugar produced by animals
>liver cells synthesize glycogen after a meal to maintain blood glucose level
TYPES OF POLYSACCHARIDES
1.STARCH;
-The major digestible polysaccharide in our diet.
-the storage form of carbohydrate in plants
-sources;wheat,rice,corn,rye,barley,potatoes,tubers etc
-two types of plant starch
1.Amylose
2.Amylopectin
AMYLOSE; is in the form of straight chain linked together with 300-5,500 glucose umits per molecules.generally it is water solubleand gives colour with iodine
AMYLOPECTIN;it contain beside straight chain several branched chains contaims 50,000-5,00,000 glucose molecules, it is insoluble in water and gives purple color with iodine
CELLULOSE; FORMS cell wall in plants
- also called fibre or ruffage
-indigestible by humans
GLYCOGEN; the storage form of glucose in body
Stored in liver and molecules
Found in tiny amounts in meat sources
Not found in plants
Not a significant food source of carbohydrate.
FUNCTIONS OF CARBOHYDRATES
>They allow for changes in the concentration gradient which influences the uptake of nutrients and water by the cells
>many polysaccharides become covalently bonded with lipids and protein to form glycolipids and glycoproteins.these glycolipids and glycoproteins are used to send message or signals between and within the cells
>they provide support to the cell wall of the plant.in insects and fungi,chitin plays an important role in providing support to the extracellular matrix around the cells
>due to presence of multiple hydrogen bonds,the water cannot invade the molecules making them hydrophobic.
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