carbohydrate

2. Lec.5
DR SHAMIM AKRAM

3. DEFINITION
 Great majority of CHO of nature occur as
polysacharides.
 > half of all organic C,50 % cellulos in wood.
 Simply known as glycans.
 Consists of more than 10 repeat units of
monosaccharides(upto hundruds and
thousands)or their derivatives held together by
glycosidic bonds.
 Linear and branched polymers.

4. CLASSIFICATION
(Based on function)
 Nutritional Polysacharides
 Starch,Glycogen,Inulin
 Structural Polysacharides
 Cellulose,Chitin,Hyaluronic acid,Chondroitin,Pectin.

5. Classification (Based on structure)
 Homopolysacharides
 Consist of same type of monomers
 Starch,Glycogen,Cellulase,Chitin,Inulin.
 Heteropolysachrides
 Consist of two or more types of monomers.
 I-Glycos-amino-glycans(GAGs)/Mucopoly sacharides
 Hyaluronic acid,Chondroitin
sulphsates,Heparin,Blood group poly.and,S.mucoids.
 II-Glyco-conjugates
 Proteoglycans,Glycoproteins and Glycolipids
 III-Mucilages
 Agar,Vegetable gums and Pectins

7. HOMOPOLYSACCHARIDES
STARCH.
 Starch is a polymer consisting of D-
glucose units.
 Starches (and other glucose polymers) are
usually insoluble in water because of the
high molecular weight, but they can form
thick colloidal suspensions with water.

8.  Main sources of starch are rice, corn, wheat,
potatoes.
 A storage polysaccharide in plants.
 It contains two polysaccharide units,amylose
and amylopectin.

9. STARCH –AMYLOSE
 Amylose consists of long unbranched chains of
Alpha D-glucose(50-5000 glucose units)
connected by glycosidic linkages.

10.  10%-20% of the starch in plants is in this form.
 Water soluble.
 Amylose forms helices (coils) which can trap
molecules of iodine, forming a characteristic
deep blue-purple color. (Iodine is often used as
a test for the presence of starch).

11. STARCH — AMYLOPECTIN
 Amylopectin consists of long chains of glucose
up to 1 million glucose units connected by
glycosidic linkages, with branches
every 24 to 30 glucose units along the chain.
 80-90% of starch is in this form in plants.

13. ACTION OF ENZYMES ON STARCH
 The enzymes hydrolyzing starch are called
amylases.
 Saliva contains salivary amylase and pancreatic
juice contains pancreatic amylase.
 These amylases are α amylases and hydrolyze
starch into maltose,isomaltose and α dextrins.

14. DEXTRINS
 These are immediate products of hydrolysis of starch
by acids or by the enzyme amylase.
 Consists of complex mixture of molecules of different
sizes and structures.
 Present in the leaves of all starch producing plants.
 Sweet in taste.
 α- dextrins have eight α -D-glucose residues showing
mostly glycosidic linkages in addition to an
linkage at each of branching site.

15. Limit Dextrin
 These are short hydrolytic remnants of
polysacharides,starch and glycogen left after exhastive
hydrolysis ,consisting of α 1-4 & α 1-6 linkages.

16. Dextrans
 Dextrans are α-D-glucopyranose
polymers,having mostly α1-6 linkages but
also have α (1,4), α (1,3) and α (1,2) linkages
with adjacent glucose molecules.
Produced when leukonostoc
mesenteroides/m.o.,having enzyme
transglucosidase, are grown in sucrose soln.
n[Sucrose][C6H10O5]n+n[Fructose]
 MW: 25,000-70,000 or upto 4000,000

17. Dextran uses
 Used as plasma substitute or extenders in the
treatment of hypovolemic shock(Haemaccel).
 Larger dextrans, which do not pass out of the
vessels, are potent osmotic agents, and thus
have been used urgently to treat hypovolemia.
 The hemodilution caused by volume expansion
with dextran use improves blood flow.
Decreases vascular thrombosis.

18.  Intravenous solutions with dextran function
both as volume expanders and means of
nutrition. Such a solution provides an
osmotically neutral fluid that once in the body
is digested by cells into glucose and free water.
 It is occasionally used to replace lost blood in
emergency situations, when replacement
blood is not available.

19.  It is used in some eye drops as a lubricant.
 also used as molecular sieves to separate
proteins and other large molecules (gel
filtration chromatography)
 component of dental plaques.

20. Glycogen
 Also known as animal starch.
 Stored in muscle and liver (mostly).
 Present in cells as granules (high MW).
 Contains both a(1,4) links and a(1,6) branches
at every 12-14glucose unit (more frequent
than in starch).

21. Glycogen
• Storage form of energy in animal.
• Stored in liver and muscle
• Stores more glucose residues per gram than starch.
• More branched and compact than starch.
• Less osmotic pressure.
• More energy in a smaller space.
• Glycogen in liver (6-8%) is higher than that in the
muscles (1-2%).
• Liver glycogen - first line of defense against declining
blood glucose levels especially between meals.

22. CELLULOSE
 A polymer consisting of long,unbranched
chains of D-glucose connected by
glycosidic linkages,may contain from
15000 glucose units in one molecule.

24. HEMICELLULOSE
 Group of high molecular weight carbohydrates
that resemble cellulose,but are more soluble
and easily decomposed.
 besides glucose, sugar monomers in
hemicellulose can include xylose, mannose,
galactose, rhamnose, and arabinose.
 Hemicelluloses contain most of the D-
pentose sugars, and occasionally small
amounts of L-sugars as well.
 Xylose is always the sugar monomer present
in the largest amount

25. Chitin
 chitin is the second most abundant
carbohydrate polymer
 Like cellulose, chitin is a structural polymer
 present in the cell wall of fungi and in the
exoskeletons of crustaceans, insects and spiders
 Consists of N-acetyl-D-glucosamine units
joined by

26. Inulin
 b-(1,2) linked fructofuranoses
 linear only; no branching
 lower molecular weight than starch
 hydrolysis yields fructose
 sources include onions, garlic etc.
 used as diagnostic agent for the evaluation of
glomerular filtration rate (renal function test)