3. Introduction
ā¢ Carbohydrates are one of the four major classes of
biological molecules.
ā¢ Carbohydrates are also the most abundant biological
molecules.
ā¢ Carbohydrates are carbon compounds that have
aldehyde (C-H=0) or ketone (C=O) moiety and
ā¢ comprises polyhyroxyl alcohol (polyhydroxyaldehyde
or polyhyroxyketone).
ā¢ Empirical formula is (CHāO)n
VETHACKING.COM
4. Functions of carbohydrates
ā¢ Serve as the storage form of energy (glycogen) to meet
the immediate energy demands of the body.
ā¢ Structural components of many organisms. These include
the fibers (cellulose) of plant,peptidoglycan of bacterial
cell walls, exoskeleton of some arthropods ,chitin of
fungal cell walls and glycosaminoglycans in animal
connective tissue)
ā¢ linked to many proteins and lipids-(glycoproteins,
glycolipids) participate in the structure of cell membrane
and cellular functions(cell growth, adhesion and
fertilization).
VETHACKING.COM
5. Functions of carbohydrates
ā¢ Most abundant dietary source of energy (4Cal/g).
ā¢ They are precursors for many organic compounds
(fats,aminoacids).
ā¢ Mucopolysaccharides form the ground substanceof
mesenchymal tissues.
ā¢ Certain carbohydrate derivatives are used as drugs, like
cardiac glycosides / antibiotics.
ā¢ Serve as metabolic intermediates.
ā¢ form part of the structural framework of RNA and DNA
ā¢ Glucose is a precursor of vitamin C in animals that can
synthesise the vitamin endogeniously such as
ruminants,cats,dogs,horses,somebirds and swine.
VETHACKING.COM
6. Classification of carbohydrates
ā¢ Carbohydrates are classified into four categories as
follows:
ļ¶Monosaccharides- a single unit of polyhydroxylketone or
aldehyde which cannot be broken down to simpler
substances on acid hydrolysis.
ļ¶Disaccharides- Two monosaccharide units joined by a
glycosidic bond.
ļ¶Oligosaccharides- 3 to about 12 monosaccharide units,
linked by glycosidic bonds.
ļ¶Polysaccharides-containmore than twelve
monosaccharide units .
VETHACKING.COM
7. Monosaccharides
ā¢ The word āMonosaccharidesā derived from the Greek
word āMonoā means Single and āsaccharideā means
sugar
ā¢ Monosaccharides are polyhydroxyl aldehydes or ketones
which cannot be further hydrolysed to simple sugar.
ā¢ Monosaccharides are simple sugars. They are sweet in
taste.They are soluble in water. They are crystallinein
nature.
ā¢ They usually contain 3 to 7 carbon atoms,2 or more
hydroxyl (OH) groups and one aldehyde (CH=O) or one
ketone (C=O) group.Infact each carbon atom contains a
hydroxyl group except the carbonyl carbon(ketone or
aldehyde carbon)
VETHACKING.COM
8. Monosaccharides
ā¢ Monosaccharides are classified in two ways.
(a) First of all, based on the number of carbon atoms
present in them and
(b) secondly based on the presence of carbonyl group.
VETHACKING.COM
10. Monosaccharides
ā¢ The aldehyde and ketone moieties of the carbohydrates
with five and six carbons will spontaneously react with
alcohol groups present in neighbouring carbons to produce
intramolecular hemiacetals or hemiketals, respectively.
ā¢ This results in the formation of five- or six-membered rings.
ā¢ The five-membered ring structure are termed furanoses
and those with six membered rings are termed pyranoses.
ā¢ Such structures can be depicted by either Fischer (linear) or
Haworth (cyclic) style diagrams.
ā¢ The numbering of the carbons in carbohydrates proceeds
from the carbonyl carbon, for aldoses,or the carbon nearest
the carbonyl, for ketoses.
VETHACKING.COM
12. Monosaccharides
ā¢ The rings can open and re-close, allowing rotation to occur
about the carbon bearing the reactive carbonyl yielding two
distinct configurations (Ī± and Ī²) of the hemiacetals and
hemiketals.
ā¢ The carbon about which this rotation occurs is the anomeric
carbon (that is carbonyl C-atom) and the two forms are
termed anomers-exist in equilibrium.
ā¢ Carbohydrates can change spontaneouslybetween the Ī± and
Ī² configurations: a process known as mutarotation.
ā¢ When drawn in the Fischer projection, the Ī± configuration
places the hydroxyl attached to the anomeric carbon to the
right, towards the ring.
ā¢ When drawn in the Haworth projection, the Ī±-configuration
places the hydroxyl downward.
VETHACKING.COM
14. Isomerism
ā¢ Compounds with same
chemical formula but
different structures
ā¢ Fructose, glucose,
mannose, and galactose
(CāHāāOā)
ā¢ Epimers differ in
configuration around only
one specific carbon atom
(with the exception of the
carbonyl carbon)
ā¢ Galactose and glucose are
C4 epimers
VETHACKING.COM
40. Properties of monosaccharides
ā¢ CHOs possess asymmetric carbon-atom that is C-atom that
has 4 different atoms or functional groups attached to it.
ā¢ Isomers exists due to the presence of asymmetric C-atom, and
number of isomers a compound has depends on the number
of asymmetric C-atoms present and is given by 2n
where n
indicates number of asymmetric C-atom in that compound.
ā¢ CHOs that differ in their configuration about a specific C-atom
other than the carbonyl C-atom are called epimers. Example;
glucose and galactose.
ā¢ If the hydroxyl group on the highest asymmetric C-atom or on
the penultimate C-atom is on the right side then the
compound will belong to the D-series while on the left side its
L-series.
VETHACKING.COM
41. Properties of monosaccharides
ā¢ CHOs that have amino group within their structure
are called amino sugars common ones are
glucosamine and galactosamine and they occur as N-
acetyl compounds.
ā¢ These compounds are important components of the
body; glucosamine is present in chitin shells of
insects and mammalian polysaccharides whereas
galactosamine is present in polysaccharides of
cartilage and chondrotin.
VETHACKING.COM
42. Properties of monosaccharides
ā¢ Monosaccharidesare able to:-
ļ¶ undergo dehydration ontreatment with strong acids to give furfural derivatives.
ļ¶ Mutarotation
ļ¶ reduce heavy metals metalliccationslike š¶š¢2+ in alkalinesolutionand high
temperature (hence termed reducing sugars)
ļ¶ form osazones with phenylhydrazine;react with dilutealkalito have reducing
action
ļ¶ aldoses can be oxidized to yield aldonicacids(first C-atom oxidized to carboxyl
group), uronic acids (terminal C-atom oxidized to carboxyl group), and aldaric or
saccharic acids(first and terminal C-atom are oxidized to carboxyl groups);
ļ¶ undergoes reduction ,glucose to sorbitol and fructose to sorbitol and mannitol;
form glycoside by the replacementof the H-atom of the hemiacetal/hemiketal
group with an organic moiety with the loss of a molecule of water.
ļ¶ When the organic moiety is not a carbohydrateitās calledAglycone. Examples are
the cardiac glycosides digoxin, indicant(CHO + indoxyl),amygdalin
(CHO+benzaldehyde)etc
VETHACKING.COM
43. Disaccharides
ā¢ 2 sugars joined by an O-glycosidic bond
ā¢ Sugars contain many hydroxyl groups, glycosidic bonds can
join one monosaccharide to another
ā¢ Multiple hydroxyl groups ā various glycosidic linkages are
possible.
ā¢ Covalent bonds between the anomeric hydroxyl of a cyclic
sugar and the hydroxyl of a second
ā¢ sugar (or another alcohol containing compound)are termed
glycosidic bonds, and the resultant molecules are glycosides.
ā¢ The linkage of two monosaccharides to form disaccharides
involves a glycosidic bond.
ā¢ Several physiologically important disaccharides are sucrose,
lactose and maltose.
VETHACKING.COM
44. Disaccharides
ā¢ Sucrose: prevalentin sugar cane and
sugar beets, is composed of glucose
and fructose through an Ī±ā(1,2)āĪ²-
glycosidic bond. On partialhydrolysis,
sucrose, yieldslevorotatory(sucrose
is dextrorotatory) equimolaramounts
of glucose and fructose calledinvert
sugar.
ā¢ In contrast to maltose and lactose,
sucrose containsno free anomeric
carbon atom; the anomeric carbons
of both monosaccharideunits are
involvedin the glycosidic bond.
ā¢ Sucrose is therefore a nonreducing
sugar.
ā¢ Non-reducing disaccharides are
named as glycosides; in this case, the
positionsjoinedare the anomeric
carbons.
VETHACKING.COM
46. Disaccharides
ā¢ Lactose: is found exclusively in the milk of mammals and consists of
galactose and glucose in a Ī²ā(1,4) glycosidic bond.
ā¢ The disaccharide lactose , which yields D-galactose and D-glucose
on hydrolysis, occurs naturally only in milk.
ā¢ The anomeric carbon of the glucose residue is available for
oxidation, and thus lactose is a reducing disaccharide. Its
abbreviated name is Gal(Ī²1 ā4)Glc.
ā¢ Maltose: the major degradation product of starch, is composed of 2
glucose monomers in an Ī±ā(1,4) glycosidic bond.
ā¢ The disaccharide maltose contains two D-glucose residues joined by
a glycosidic linkage between C-1 (the anomeric carbon) of one
glucose residue and C-4 of the other.
ā¢ Because the disaccharide retains a free anomeric carbon (C-1 of the
glucose), maltose is a reducing sugar.
ā¢ Oligosaccharides -contain 3-12 monosaccharide units e.g maltotriose
(Glucose + Glucose + Glucose).
VETHACKING.COM
50. Polysaccharides
ā¢ Most of the carbohydrates found in nature occur in the
form of high molecular weight polymers called
polysaccharides.
ā¢ The monomeric building blocks used to generate
polysaccharides can be varied; in all cases, however, the
predominant monosaccharide found in polysaccharides is
D-glucose.
ā¢ When polysaccharides are composed of a single
monosaccharide building block, they are termed
homopolysaccharides.
ā¢ Polysaccharides composed of more than one type of
monosaccharide are termed heteropolysaccharides.
VETHACKING.COM
51. Polysaccharides
Glycogen
ā¢ Glycogen is the major form of stored carbohydrate in animals.
ā¢ This crucial molecule is a homopolymer of glucose in Ī±ā(1,4)
linkage; it is also highly branched, with Ī±ā(1,6) branch linkages
occurring every 8-10 residues.
ā¢ Glycogen is a very compact structure that results from the coiling of
the polymer chains.
ā¢ This compactness allows large amounts of carbon energy to be
stored in a small volume, with little effect on cellular osmolarity.
ā¢ The structure of glycogen is similar to that of amylopectin, although
the branches in glycogen tend to be shorter and more frequent.
ā¢ The liver and skeletal muscles are major depots of glycogen.
ā¢ Glycogen is broken back down into glucose when energy is needed
(a process called glycogenolysis).
VETHACKING.COM
54. Polysaccharides
Starch
ā¢ Starch is the major form of stored carbohydrate in plant cells. Its structure is
identical to glycogen, except for a much lower degree of branching (about
every 20ā30 residues).
ā¢ Unbranched starch is called amylose; branched starch is called amylopectin.
ā¢ Starches are insoluble in water and thus can serve as storage depots of glucose.
ā¢ Plants convert excess glucose into starch for storage.
ā¢ Before starches can enter (or leave) cells, they must be digested.
ā¢ The hydrolysis of starch is done by amylases.
ā¢ With the aid of an amylase (such as pancreatic amylase), water molecules enter
at the 1 -> 4 linkages, breaking the chain and eventually producing a mixture of
glucose and maltose.
ā¢ A different amylase is needed to break the 1 -> 6 bonds of amylopectin.
VETHACKING.COM
55. Starch
ā¢ Amylose consists of linear, unbranched chains of several hundred glucose residues
(units).
ā¢ The glucose residues are linked by a glycosidic bond between their number 1 and 4
carbon atoms.
ā¢ Amylopectin differs from amylose in being highly branched.At approximately every
thirtieth residue along the chain, a short side chain is attached by a glycosidic bond to the
#6 carbon atom (the carbon above the ring).
ā¢ The total number of glucose residues in a molecule of amylopectin is several thousands
VETHACKING.COM
61. Cellulose
ā¢ It is the major structuralmaterial of which plantsare made.
ā¢ Wood is largely cellulose while cotton and paper are almost pure cellulose.
ā¢ Like starch, celluloseis a polysaccharidewith glucose as its monomer.
However, cellulosediffers profoundlyfrom starch in its properties.
ā¢ Because of the orientation of the glycosidic bonds linking the glucose
residues, the rings of glucose are arranged in a flip-flop manner.
ā¢ This producesa long, straight, rigid molecule.
ā¢ There are no side chains in celluloseas there are in starch.
ā¢ The absence of side chains allows these linear molecules to lie close
together.
ā¢ Because of the many -OH groups, as well as the oxygen atom in the ring,
there are many opportunitiesfor hydrogen bondsto form between adjacent
chains.
VETHACKING.COM
62. Cellulose
ā¢ Chains associate in groups of about 1000 to form cellulose
microfibrils,which in turn associate with each otherto form a cellulose
macrofibrils which results in a moleculewith high tensile strength.
ā¢ In starch the Ī±-1,4 glycosidic bondscause the chains to coil helicallybut in
cellulosethe bonds cause celluloseto form straight chains which are
rigid,this is attributedto the fact that to make an Ī±-1,4 glycosidic bond one
Ī²-glucose moleculerotates through 180į¶± preventing the helical coiling
which allows chains to pack closely to form rigid ropes.
ā¢ It is the main constituent of supportingtissues of plantsand therefore forms
a considerablepart of animal vegetable diet.
ā¢ Herbivores with the help of bacteria can utilize a considerableproportionof
cellulose.
ā¢ It adds bulk to the intestinal contents(roughage) therebystimulating
peristalsis and elimination of indigestible food residues.
VETHACKING.COM
64. Dextrin
ā¢ Partial hydrolyticproductsof starch by Ī±-amylase, Ī²-amylase or acids give
what is called dextrins that have lower molecularweight but resemble
starch in being precipitableby alcohol and have a free sugar group and can
thus reduce alkalinecopper sulphatesolution.
ā¢ Dextrin solutionsare often used as mucilages (sticky gums) and are widely
used in infant feeding.
ā¢ Limit dextrins are well defined dextrissn formed on total hydrolysis of
starch by Ī²- amylase.
VETHACKING.COM
66. Polysaccharides
Inulin
ā¢ It is a polymer of D-fructose with low molecular weight of about 5000.
ā¢ It occurs in tubers of Dehlia, bulbs of onions and garlic etc. it can be hydrolysed by
acid and inulinase to D-fructose.it is used in physiological investigation for
determination of glomerular filtration rate and in estimation of total body water.
Dextrans
ā¢ Synthesized by the action of leuconostoc mesenteriodes (a bacterium) in sucrose
medium, it is a polymer of D-glucose.
ā¢ They are different from dextrins in structure but have D-glucose units joined by Ī±1-
4, Ī± 1-6, Ī±; 1-3 glycosidic linkages joined together to form a network.
ā¢ Dextran solutions have a mol. wt of about 75000 and are used as plasma expanders
because they have the ability to increase blood volume because high viscosity, low
osmotic pressured slow disintergration and utilization and slow elimination from
the body they remain in the blood for many hours to exert its effect.
VETHACKING.COM
69. Agar
Agar
ā¢ It is a homopolysaccharide made up of repeating units of galactose
which is sulphated.
ā¢ It is present in sea weed.
ā¢ It is used as a laxative in constipation because like cellulose it is not
digested hence adds bulk to faeces and helps propulsion.
ā¢ In microbiology it is purified and dissolved in hot water and on
cooling sets like gel and used in culture of bacteria.
VETHACKING.COM
71. Heteropolysaccharides/Mucopolysaccharides
ā¢ These are made up of mixed disaccharide repeatingunits and on hydrolysis
gives a mixture of more than one productsof monosaccharidesand their
derivatives of amino sugars and uronic acids.
ā¢ The hexamine present is usually acetylatedand these compoundsare
essentially componentsof tissues where they are generally present either in
free form or in combination with proteins.
ā¢ There are 2 major classes of MPS (mucopolysaccharides)
ļ¶ Neutral MPS e.g. bloodgroup substances
ļ¶ Acidic MPS
ā¢ Acid MPS are present in connective tissue and have hexamine as the
repeating disaccharideunits with alternating1,4 and 1,3 linkages.
VETHACKING.COM
72. Heteropolysaccharides/Mucopolysaccharides
ā¢ Hyaluronic acid; it is sulphate free and found in vitreous humour, synovial
fluid, skin, umbilical cord and rheumatic nodule. it occurs as both free and in
salt like combination with proteins hence called the ground substance of
mesenchyme and integral part of the gel-like ground substance of C.T and other
tissues.
ā¢ Composed of repeating units of N-acetyl glucosamine and D-glucuronic acid.
Heparin
ā¢ It is an anticoagulant present in liver and is produced mainly by mast cells of
liver.
ā¢ It can also be found in lungs, thymus, spleen, walls of large vessels, skin etc.
both the hydroxyl and the amino groups are combined with sulphuric acid.
ā¢ Repeating disaccharide units are D-glucosamine and either D-glucuronic acid
or L-iduronic acid.
ā¢ There is a Ī±;1-4 linkage from the anomeric C-atom of the glucuronic acid to the
C4 hydroxyl group of the glucosamine.
VETHACKING.COM
73. Heteropolysaccharides/Mucopolysaccharides
Chondroitin sulphates
ā¢ They are present in connective tissue and serve as structural material such as cartilage,
tendons and bones.
ā¢ It differs from hyaluronic acid in that it has N-acetyl galactosamine instead of N-acetyl
glucosamine.
ā¢ There are 4 different types of chondroitin SO4s named as Chondroitin
ā¢ Sulphate-A,B,C and D. these differ at points of C-atom linkages, positions and /or
number of sulphate groups etc
Heparin sulphate
ā¢ It has been isolated from amyloid liver (a diseased state) and certain normal tissue such
as human and cattle aorta.
ā¢ It has negligible anticoagulant activity and though structurally similar to heparin has a
lower mol. wt. unlike heparin its predominant uronic acid is D- glucurononic acid
Sialic acids
ā¢ These are N-acetyl derivatives of neuraminic acid and are widely distributed in tissues
and are present in blood group substances.
ā¢ Neuraminic acid is a condensation product of pyruvic acid and mannosamine.
VETHACKING.COM
82. Glycoproteins
ā¢ One or several oligosaccharides joined covalently to a
protein
ā¢ Product of posttranslational modification
ā¢ Present on the outer cell membrane, ECF & blood
ā¢ Carbohydrate moieties are smaller and more structurally
diverse than the glycosaminoglycans of proteoglycans
ā¢ Attached at its anomeric carbon through a glycosidic link to:
ļ the -OOH of a Ser or Thr residue (O-linked)
ļ through an N-glycosyl link to the amide nitrogen of an Asn
residue (N-linked)
ā¢ Important for cell adhesion and signaling
VETHACKING.COM
84. Proteoglycans
ā¢ Macromolecules of the cell surface or
extracellular matrix
ā¢ Glycosaminoglycan chains are joined covalently
to a protein
ā¢ Glycosaminoglycans are made of disaccharide
repeating units containing a derivative of an
amino sugar
ā¢ N-acetylglucosamine /N-acetylgalactosamine; D-
glucuronic/L-iduronic acid.
ā¢ Major components of connective tissue such as
cartilage
VETHACKING.COM
85. Proteoglycans
ā¢ These are conjugated proteins. Core proteins are covalentlylinked to
glycosaminoglycans (GAGS).
ā¢ The amount of carbohydratesin proteoglycansis up to 95%, higher than
that in glycoproteins.
ā¢ These compoundsare constituentsof extracellularmatrix or ground
substance; they interact with collagen and elastin.
ā¢ They also act as polyanions, barriers in tissues, lubricants, in release of
hormones etc.
VETHACKING.COM
