By Prakash Pokhrel Biochemistry Lecture.

1. CARBOHYDRATES
Prakash Pokhrel

2. CARBOHYDRATES
•Most abundant organic compounds in the
plant word
•Act as storehouses of chemical energy
•Components of supportive structures in
plants
•Crustacean shells
•Connective tissues in animals
•Essential components of nucleic acids

3. CARBOHYDRATES
•means “hydrate of carbon”
•derives from the formula Cn(H2O)m
•Glucose: C6H12O6 or C6(H2O)6
•most are polyhydroxyaldehydes,
polyhydroxyketones, or compounds that yield
them after hydrolysis
•saccharides – simpler members of the CHO
family (Latin: saccharum – sugar)
•Monosaccharide, Disaccharide, Oligosaccharide,
and Polysaccharide

4. A. MONOSACCHARIDES
•C6H12O6
•with one of the carbons being the carbonyl
group of either an aldehyde or a ketone
•have 3 to 9 carbon atoms
•-ose indicates that a molecule is a
carbohydrate
•tri-, tetr-, pent-, so and so forth - indicate the
number of carbon atoms in the chain

5. A. MONOSACCHARIDES
•Aldoses
•monosaccharides
containing an aldehyde
group

6. A. MONOSACCHARIDES
•Ketoses
•monosaccharides
containing a ketone
group

7. A. MONOSACCHARIDES
•2 Trioses
•aldotriose
glyceraldehyde
•ketotriose
dihydroxyacetone

8. A. MONOSACCHARIDES
•Fischer Projection Formulas
•Glyceraldehyde – contains a stereocenter
and therefore exists as a pair of enantiomers
•Enantiomer - is one of two stereoisomers that are
non-superposable complete mirror images of each
other, much as one's left and right hands are "the
same" but opposite

9. A. MONOSACCHARIDES
•D- and L-
Monosaccharides
•D-Monosaccharide
•has the –OH group
on its penultimate
carbon to the right
•L-Monosaccharide
•has the –OH group
on its penultimate
carbon to the left

11. A. MONOSACCHARIDES
•D-
•specifies the configuration
at the stereocenter farthest
from the carbonyl group
•Prefixes (rib-, arabin-,
and gluc-)
•specify the configuration
of all other stereocenters in
the monosaccharide relative
to one another
•-ose
•indicates that the
compound is a carbohydrate

12. A. MONOSACCHARIDES
•Most Abundant
Hexoses
•D-Glucose
•D-Galactose
•D-aldohexoses
•D-Fructose
•D-ketohexose

13. A. MONOSACCHARIDES
•Amino Sugars
•a monosaccharide in which an –OH group is
replaced by an –NH2 group
•D-Glucosamine
•D-Mannosamine
•D-Galactosamine

14. A. MONOSACCHARIDES
•Physical Properties
•are colorless, crystalline solids
•Are very soluble in water
•because hydrogen bonding is possible
between their polar –OH groups and water
•Slightly soluble in ethanol
•Insoluble in nonpolar solvents such as
diethyl ether, dicloromethane, and benzene

15. A. MONOSACCHARIDES
•Cyclic Structure
•Haworth Projection
•A way to view furanose and pyranose forms
of monosaccharides
•The ring is drawn flat and viewed through its
edge with the anomeric carbon (new C
stereocenter created in forming the cyclic
structure) on the right and the oxygen atom
to the rear
•A 5- or 6-membered cyclic hemiacetal is
represented as a planar pentagon or
hexagon, respectively, lying roughly
perpendicular to the plane of the paper

17. A. MONOSACCHARIDES
•Cyclic Structure
•Haworth Projection
•β means that the –OH on the anomeric
carbon lies on the same side of the ring as
the terminal –CH2OH
•α means that the –OH on the anomeric
carbon lies on the side of the ring opposite
from the terminal –CH2OH

19. A. MONOSACCHARIDES
•Cyclic Structure
•Haworth Projection
•-pyran- a 6-membered hemiacetal ring
•-furan- a 5-membered hemiacetal ring
•Pryanose and Furanose
•Are used because monosacharide 5- and
6-membered rings correspond to the
heterocyclic compunds pyran and furan

21. REACTIONS OF
CARBOHYDRATE

22. REACTION OF MONOSACCHARIDES
•Formation of Glycosides (Acetals)
•Acetal – yields when hemiacetal is treated
with one molecule of alcohol
•Glycoside
•A carbohydrate in which the –OH group on
its anomeric carbon is replaced by an –OR
group
•Glycosidic Bond
•the bond from the anomeric carbon of a
glycoside to an –OR group

23. Glycosides
 The hydroxyl group of anomeric carbon of a
carbohydrate can join with a hydroxyl group
of another carbohydrate or some other
compound to form a glycoside and the bond
so formed is known as glycosidic bond.
 eg. R-OH + HO-R’ R-O-R' + H2O
 The non-carbohydrate moiety is known as
aglycone –phenol, sterol, glycerol and
methanol.
 Glycosidic bond can be N-linked or, O-
linked.

24.  Streptomycin
◦ Antibiotic
◦ Given in Tuberculosis

25.  Cardiac Glycosides –Digoxin, Digitoxin
◦ Used in cardiac insufficiency.
◦ Stimulate cardiac muscle contraction.
◦ Contain steroids as aglycone
component.
 Ouabain –Sodium pump inhibitor.

26. Formation of Esters
 Esterification of alcoholic groups of
monosaccharides with phosphoric
acid is a common reaction in
metabolism.
 Examples :Glucose-6-phosphate, and
Glucose-1-phosphate.
 ATPdonates the phosphate moiety.

27. Glucose oxidase test
 Glucose + O2
Glucose Oxidase
Gluconolactone + H2O2
 H2O2 + (reduced colourless dye)
Peroxidase
(Oxidized colored dye)

28. Osazone Formation
 All reducing sugars will form
osazones with excess of phenyl
hydrazine when kept at boiling
temperature.
 Glucose, Galactose and Fructose will
produce the same needle-shaped
crystals.

30. Molisch’s test
 All carbohydrates when treated with conc.
sulphuric acid undergo dehydration to
give fufural compounds. These
compounds condense with Alpha-napthol
to form colored compounds.
 Molish test is given by sugars with at
least five carbons because it involves
furfural derivatives, which are five carbon
compounds.

31. Purple ring at junction

32. Fehling’s test
Same principle as benedicts test
Fehling’s A contains 7% copper
sulphate and Fehling’s B contains
sodium potassium tartarate.

33. Oxidation
The glucuronic acid is used by the body for
conjugation with insoluble molecules to make them
soluble in water for detoxification purpose and also
for synthesis of heteropolysaccharides.

34. Reduction to Form Alcohols
 When treated with reducing agents
hydrogen can reduce sugars. Aldose yields
corresponding alcohol.
 Glucose is reduced to sorbitol
 mannose to mannitol
 fructose becomes sorbitol and mannitol
 Galactose is reduced to dulcitol and
 ribose to ribitol.

35. Significance of reduction
 Sorbitol, mannitol and dulcitol are
used to identify bacterial colonies.
 Mannitol is also used to reduce
intracranial tension by forced
diuresis.
 The osmotic effect of sorbitol produces
changes in tissues when they
accumulate in abnormal amounts, e.g.
cataract of lens.

36. Cataract
Retinopathy
Nephropathy
Neuropathy

37. In maltose and lactose, there is still
One carbonyl group attaching the 1st carbon
Not engaged in the formation of glycosidic bond.
It is reductable.
So, they are still reducing sugars.
In sucrose, both reductable carbonyl groups
Are involved in the formation of glycosidic bond.
So, it is a non-reducing sugar
The decomposition of disaccharides into
monosaccharides is called hydrolysis,
Because one molecule of water should be added.

38. B. DISACCHARIDES and OLIGOSACCHARIDES
•Disaccharides
•Sucrose (table
sugar)
•most
abundant
•obtained
principally from
the juice of
sugar cane and
sugar beets
•nonreducing
sugar

39. B. DISACCHARIDES and OLIGOSACCHARIDES
•Disaccharides
•Lactose
•principal sugar
present in milk
•consists of D-
galactopyranose
bonded by a
beta-1,4-
glycosidic bond
to carbon 4 of D-
glucopyranose
•reducing sugar

40. B. DISACCHARIDES and OLIGOSACCHARIDES
•Disaccharides
•Maltose
•derives its name
from its presence
in malt, the juice
from sprouted
barley and other
cereal grains
•consists of 2 units
of D-glucopyranose
joined by a glycosidic
acid between carbon
1 of one unit and
carbon 4 of the other
unit

42. Sucrose
When sucrose is hydrolyzed, the products have
reducing action.
A sugar solution which is originally non-reducing,
but becomes reducing after hydrolysis, is
inferred as sucrose (specific sucrose test).
Benedict's test is positive for
glucose. Test is negative for
sucrose; but when sucrose is
hydrolyzed, the test becomes
positive (specific sucrose test)

43. B. DISACCHARIDES and OLIGOSACCHARIDES
•Relative Sweetness
•Fructose
•sweetest – even sweeter than sucrose
•Honey
•D-fructose and D-glucose
•Lactose
•almost no sweetness and is sometimes added
to food as a filler

44. C. POLYSACCHARIDES
•Polysaccharides
•Starch: Amylose and Amylopectin
•used for energy storage in plants
•complete hydrolysis yields only D-Glucose
•Amylose – composed of continuous,
unbranched chains of as many as 4000 D-
glucose units joined by alpha-1,4-glycosidic
bonds
•Amylopectin – contains chains of as many
as 10,000 D-glucose units joined by alpha-
1,4-glycosidic bonds
• new chains of 24-30 units are started by
alpha-1,6-glycosidic bonds

46. •Cellulose
•most widely distributed plant skeletal
polysaccharide
•is a linear polysaccharide of D-glucose units
joined by beta-1,4-glycosidic bonds

47. Physical property of polysaccharides
(1) Polysaccharides are insoluble in water
and cannot give any taste.
(2) As it cannot be dissolved in water,
polysaccharides cannot move across the
plasma membrane of the cell and
cannot change the water potential of the
water body.
(3) No optical activity can be observed

48. Homopolysaccharides
Starch
Glycogen
Cellulose
Inulin
Dextrans
Chitin

49. Starch
 It is the reserve carbohydrate of plant
kingdom
 Sources: Potatoes, cereals (rice,
wheat) and other food grains.
 Starch is composed of amylose and
amylopectin.

50. Amylose
Amylopectin
OH
0
OH OH
0 0
OH
0
OH OH
n OH
0
n OH

51.  Amylose is made up of glucose units
with alpha-1,4 glycosidic linkages to
form an unbranched long chain. Water
soluble.
 The insoluble part absorbs water and
forms paste like gel; this is called
amylopectin.
 Amylopectin is also made up of
glucose units, but is highly branched.
The branching points are made by
alpha-1,6 linkage

52. Iodine test for starch
 Starch will form a blue colored
complex with iodine; this color
disappears on heating and reappears
when cooled. This is a sensitive test
for starch.
 Starch is nonreducing because the
free sugar groups are negligible in
number.

54. Glycogen

55.  It is the reserve carbohydrate in animals.
It is stored in liver and muscle.
 Liver glycogen stores increase during the
well-fed state , and are depleted during a
fast.
 Glycogen is composed of glucose units
joined by alpha-1,4 links in straight
chains. It also has alpha-1,6 glycosidic
linkages at the branching points.
 Glycogen is more branched and more
compact than amylopectin.

56. Liver and muscle glycogen

57. Cellulose
 It is made up of glucose units combined
with beta-1,4 linkages.
 It has a straight line structure, with no
branching points.
 Beta-1,4 bridges are hydrolyzed by the
enzyme cellobiase. But this enzyme is
absent in animal and human digestive
system, and hence cellulose cannot be
digested.

58. Importance
Fiber can absorb 10–15 times its own
weight in water, drawing fluid into
the lumen of the intestine
Increasing bowel motility
1.Decrease the risk for constipation
It is a major constituent of fiber, the
nondigestable carbohydrate.

59. Intestine
Bile salt Fibers
Excreted
Cholesterol
Decreases
serum
cholesterol
level
.
2. Lower LDL cholesterollevels

60. Delays gastric emptying and can result in a
sensation of fullness
4. Reduced peaks of blood glucose
following a meal
Can bind various toxic substances
including carcinogens & eliminate them in
faecal matter
3.Decreases chances of some cancers

61. Inulin
 It is a long chain homoglycan composed
of D-fructose units with repeating beta-1,2
linkages.
 It is the reserve carbohydrate present in
various bulbs and tubers, such as onion,
garlic.
 It is clinically used to find renal
clearance value and glomerular
filtration rate.

62. Dextrans
 These are highly branched homopolymers
of glucose units with 1-6, 1-4 and 1-3
linkages. They are produced by micro-
organisms.
 Since they will not easily go out of
vascular compartment, they are used for
intravenous infusion as plasma volume
expander for treatment of hypovolemic
shock.

63.  D-glucose is otherwise called Dextrose, a
term often used in bed-side medicine, e.g.
dextrose drip.
 Dextrin is the partially digested product of
starch.
 Dextran is high molecular weight
carbohydrate, synthesized by bacteria.

64.  It is present in exoskeletons of
insect. It is composed of units
of N- acetylglucosamine
with beta-1,4 glycosidic
linkages.

65. Heteropolysaccharides
• . Agar
• Mucopolysaccharide

66. Agar
 Agar = The linear polysaccharide Agarose
+ agaropectin
 It is dissolved in water at 100ºC, which
upon cooling sets into a gel. Agarose is
used as matrix for electrophoresis.
 Agar cannot be digested by bacteria and
hence used widely as a supporting agent to
culture bacterial colonies.

67. Mucopolysaccharide
glycosaminoglycans(GAGs)
 [acidic sugar–amino sugar]n.

68.  Because of their large number of negative
charges, these heteropolysaccharide chains
tend to be extended in solution. They repel
each other, and are surrounded by a shell
of water molecules. When brought
together, they “slip” past each other.
 This produces the “slippery” consistency
of mucous secretions and synovial fluid.

69. Importance
Amino sugars Found in
Glucosamine Hyaluronic acid, heparin and
blood group substances
Galactosamine Chondroitin sulphate of
cartilage, bone and tendons.
Mannosamine constituent of glycoproteins
N-acetylglucosamine
(GluNac) and N-
acetyl galactosamine
(GalNac)
constituents of
glycoproteins,
Mucopolysaccharide and cell
membrane antigens.

70. GAGs Composition Tissue distribution Functions
Hyaluronic
acid
D-glucuronic acid
and N-acetyl D-
glucosamine
Connective tissue
Synovial fluid
Vitreous humor
Gel around ovum
lubricant and shock
absorbant in joints
Chondroitin
sulphate
D-glucuronic acid and N-
acetyl D-galactosamine
4-sulfate.
bone, cartilage,
Tendons,heart
valves and skin.
Helps to maintain
the structure And
shapes of tissues
Dermatan
sulfate
D-Iduronic acid and
N-acetyl D-galactosamine
4 –sulfate.
Skin Helps to maintain
shapes of tissues
Keratan
sulphate
galactose and N-acetyl
glucosamine
cornea
tendons
Keeps cornea
Transparent
Heparin sulphated glucosamine
and glucuronic acid or
iduronic acid
blood, lung, liver
,kidney, spleen
Anticoagulant
Clearing factor

71. Hyaluronidase
Breaks b(1-4 linkages) in hyaluronic acid.
Present in high concentration in testes,
seminal fluid, and in certain snake and insect
venoms.
Hyaluronidase of semen clears the gel
(hyaluronic acid) around the ovum allowing a
better penetration of sperm into the ovum.
Serves important role in fertilization
Hyaluronidase of bacteria helps their invasion
into the animal tissues.

72.  Heparin is an anticoagulant( prevents
blood clotting).
 Heparin helps in the release of the enzyme
lipoprotein lipase which helps in clearing
the turbidity of lipemic plasma.
 Lipoprotein lipase breaks TG in glycerol
and FFA.

73.  Proteoglycans: When carbohydrate
chains are attached to a polypeptide chain.
 Glycoproteins: Carbohydrate content ≤
10%.

74. Glycoprotein Major function
Glycophorin glycoprotein of
erythrocytes cell
membrane
Collagen Structure of cartilage
and bone
Ceruloplasmin Transport protein
Immunoglobulin Defense against
infection
Intrinsic factor Absorption of vitamin
B12
Fibrinogen Blood clotting

75. Thank you