Chemistry try of carbohydrates

1. Polysaccharides
• They are classified into:
A-Homopolysaccharides
B-Heteropolysaccharides.

2. A-Homopolysaccharides
• They yield only one type of monosaccharides on
hydrolysis and they are named according to the
type of that monosaccharide, e.g.,
• Hexosans + H2O  Hexoses
• Pentosans + H2O  Pentoses

3. Hexosans: 6 carbon sugars
I. Glucosans:
• They produce only glucose on hydrolysis.
• They include; starch, dextrins, dextrans,
glycogen and cellulose
• Plants store glucose as amylose or amylopectin,
glucose polymers collectively called starch.

4. A. Starch:
• It is the stored form of carbohydrate of plants.
It never exists in animals.
• It is present in cereals such as wheat and rice
and tubers such as potatoes.
• It is in the form of starch granules. The core of
the granule is amylose (20%) and the shell is
amylopectin (80%).
• Due to its high molecular weight it forms
colloidal solution in hot water.
S t a r c h g r a n u l e
A m y lo s e
A m y lo p e c t i n

5. O
H H
H
OH
H
OH
CH2OH
H
O
H H
OH
H
OH
CH2OH
H
O
Amylose
1
4
n
O
O
1 4
1. Amylose:. Straight chain compound present in the
form glucose units linked by -1,4-glucosidic bond of
a helix formed of a large number of - glucose.
It forms the inner part of
starch granules
H O
OH
H
OH
H
OH
CH2OH
H
O H
H
OH
H
OH
CH2OH
H
O
H
H H O
O
H
OH
H
OH
CH2OH
H
H H O
H
OH
H
OH
CH2OH
H
OH
H
H O
O
H
OH
H
OH
CH2OH
H
O
H
1
6
5
4
3
1
2
amylose

6. .
• 2. Amylopectin:
• It forms the outer coat of starch granule and is
insoluble in water.
• It is branched chains formed of a large number of
-glucose units linked by -1,4-glucosidic linkage
along the branch and by -1,6-glucosidic linkage
at the branching point that occur every 25-30
glucose units. Due to its high molecular weight,
it forms a colloidal solution.
• Starch can be hydrolyzed by HCl or amylase.

7. Amylopectin is a glucose polymer with mainly (14)
linkages, but it also has branches formed by (16)
linkages. Branches are generally longer than shown above.
The branches produce a compact structure & provide
multiple chain ends at which enzymatic cleavage can occur.
H O
OH
H
OH
H
OH
CH2OH
H
O H
H
OH
H
OH
CH2OH
H
O
H
H H O
O
H
OH
H
OH
CH2
H
H H O
H
OH
H
OH
CH2OH
H
OH
H
H O
O
H
OH
H
OH
CH2OH
H
O
H
O
1 4
6
H O
H
OH
H
OH
CH2OH
H
H H O
H
OH
H
OH
CH2OH
H
H
O
1
OH
3
4
5
2
amylopectin

8. .
O
H H
H
O
H
H
O
H
CH
2O
H
H
O
H H
O
H
H
O
H
CH
2O
H
H
O
Amylopectin
1
4
O
1 4
O
H H
H
O
H
H
O
H
CH
2O
H
H
O
H H
O
H
H
O
H
CH
2O
H
H
O
1
4
O
O
1 4
O
H H
H
O
H
H
O
H
CH
2
H
O
H H
O
H
H
O
H
CH
2O
H
H
O
1
4
n
O
1 4
6
O

9. B. Dextrins:
• Products of hydrolysis of starch and include
amylodextrin, erythrodextrin, achrodextrin which
form color with iodine
• They have sweet taste.
• They are easily digested than starch as in corn and
rice syrup.

10. .
C. Dextran:
• A compound formed of -glucose units linked
by -1,4, -1,3- and -1,6-linkage present in the
form of a network that is synthesized by certain
bacteria having sucrose in its media.
It has a great biochemical importance,
1. It is used as plasma substitute to restore blood
pressure in cases of shock.
2. Iron used for treatment of iron deficiency
anemia is used as dextran ferrous sulfate
intramuscular injection.
3. Sodium dextran sulfate is an anticoagulant.

11. .
D. Glycogen:
• It is the stored form of carbohydrate in animal,
particularly in muscles and liver.
• Its structure is similar to amylopectin a
branched tree with -1,4-glucosidic linkage
along the branch and -1,6-glucosidic linkage at
the branching point.
• The glycogen tree is shorter and more branched
(a branch point every 8-10 glucose units) than
amylopectin.
• It is digestible because human amylases
hydrolyze -glucosidic linkage.

12. .
The glycogen molecule. A:
General structure.
The chains are either
branched or unbranched
and are arranged in 12
concentric layers (only four
are shown in the figure).
The branched chains (each
has two branches) are
found in the inner layers
and the unbranched chains
in the outer layer. (G,
glycogenin, the primer
molecule for glycogen
synthesis.)
Liver glycogen helps to maintain blood glucose level

13. Glycogen, the glucose storage polymer in animals, is similar in
structure to amylopectin.
But glycogen has more (16) branches.
The highly branched structure permits rapid glucose release
from glycogen stores, e.g., in muscle during exercise.
The ability to rapidly mobilize glucose is more essential to
animals than to plants.
H O
OH
H
OH
H
OH
CH2OH
H
O H
H
OH
H
OH
CH2OH
H
O
H
H H O
O
H
OH
H
OH
CH2
H
H H O
H
OH
H
OH
CH2OH
H
OH
H
H O
O
H
OH
H
OH
CH2OH
H
O
H
O
1 4
6
H O
H
OH
H
OH
CH2OH
H
H H O
H
OH
H
OH
CH2OH
H
H
O
1
OH
3
4
5
2
glycogen

14. E. Cellulose:
• It is a structural polysaccharide and forms the
skeleton of plant cells and does not enter in
animals cell structures.
• It is a straight chain molecule formed of a large
number of -glucose units linked by -1,4-
glucosidic linkage.
• It is water insoluble and enters in structure of
cotton and paper
• It is the major food for herbivorous animal
where it is fermented into volatile fatty acids.
• It gives cellobiose on hydrolysis with HCl.

15. .
• It is indigestible but is very essential in food for:
1. Prevention of constipation by increasing the
bulk of stools.
2. Its fermentation by large intestinal bacteria give
volatile fatty acids that is anticancer for colon
cells and gives also some water soluble
vitamins.
3. It adsorbs toxins present in foods and prevents
its absorption into the body.
cellulose
H O
OH
H
OH
H
OH
CH
2OH
H
O
H
OH
H
OH
CH
2OH
H
O
H H O
O H
OH
H
OH
CH
2OH
H
H O
H
OH
H
OH
CH
2OH
H
H
OH
H O
O H
OH
H
OH
CH
2OH
H
O
H H H H
1
6
5
4
3
1
2

16. Starch Glycogen Cellulose
1.Nature:
Stored form of carbohydrate in plants.
Stored form of
carbohydrates in animals.
Structural form of
carbohydrate in plant cells
but prevents constipation
in human.
1.Source:
Cereals, e.g., wheat, rice, and tubers, e.g.,
potatoes.
Muscles and liver Linen and cotton are nearly
pure cellulose.
1.Solubility:
Amylose is water soluble and amylopectin
is insoluble.
Water soluble forming
colloidal solution.
Water insoluble.
1.Nature of the chains:
Amylose is helical straight chain (-glucose
units linked by -1,4-glucosidic bonds).
Amylopectin is branched chain (-glucose
units linked by -1,4- and -1,6-glucosidic
bonds).
Branched chain similar to
amylopectin but its
trees are shorter and
have more branches
than amylopectin
tree.
Straight chain (large number of
-glucose units linked by
-1,4- glucosidic bonds).
1.Reaction with iodine:
Amylose gives blue color and amylopectin
gives red color.
Gives red color. No color.
1.Digestibility:
Is hydrolyzed by HCl or amylase into
dextrins and maltose.
Digestible by amylase
into dextrins and
maltose.
Non-digestiblebut HCl
hydrolysis gives cellobiose.

17. .
II. Fructosans:
• They are formed of fructose as a building unit such
as Inulin.
Inulin:
• It is formed of fructose only and present in onions.
• It is not metabolizible in human body, therefore, it
is used in evaluation of kidney function as a part of
inulin clearance test.

18. .
III. Galactosans:
- They are formed of galactose as the building units
such as agar-agar.
- Biochemical importance:
1. It is used for growth of bacteria and mammalian
cells in culture.
2. It imbibes water and increases intestinal
contents to prevent and treat constipation.
3. Some electrophoresis gels is formed of it.

19. .
IV. N-acetyl-glucosan:
• It is a homopolysaccharide formed of -N-acetyl-
glucosamine units such as chitin of insects.
• Chitin:
• It is a homopolysaccharide formed of -N-acetyl-
glucosamine units linked by -1,4-glucosidic
linkage present in the exoskeleton of insects.

20. .
O
H
H
H
NH-CO-
CH3
H
OH
CH2OH
H
O
H
H
H
NH-CO-
CH3
H
OH
CH2OH
H
O O
O
Chitin
-N-acetyl-glucosamine -N-acetyl-glucosamine
n
1 4 1
4
Polymer of N-acetylglucosamine.

21. .
B-Heteropolysaccharides
• They are polysaccharides that on hydrolysis
produce several types of sugars. There are two
types:
1. Non-nitrogenous heteropolysaccharides
2. Nitrogenous heteropolysaccharides.

22. .
A-Non-nitrogenous heteropolysaccharides:
They do not contain sugar amines, such as pectin and
plant gums. Also called Mucilages
1-Plant gums :
• They are exudates of plants that do not contain
amino sugars.
• They contain pentoses, hexoses and uronic
acids, e.g., Gum Arabic which is rich in
arabinose.
• They are emulsifying agents.

23. .
• Mucilages: These are of plant origin and include
agar, vegetable gums and pectins.
• Hemiclellulose is a polymer of aldopentose [beta–
D xylose]. It occurs with pectin [D–galacturonic
acid] residues and a protein extensin in plant cell
walls.
• This heteropolysaccharide acts as a cementing
material, provides shape and support to the plant
tissues.

24. .
2. Pectin:
• They are present in pulp of fruits and are
responsible for settling of jams.
• They are formed of pentoses, hexoses, uronic
acids mainly galacturonic acid.
• They are water soluble formed from a water
insoluble compound called pectose present in
raw fruits which is transformed into pectin by
the action of sunlight, heat and pectase enzyme
when fruits are ripened.

25. .
• Biochemical importance of pectin:
1. Emulsifying reagents.
2. Demulcents.
3. Responsible for settling of jams.
4. They increase in size when they absorb water
forming a jell and so they are used in the
treatment of infantile diarrhea.

26. .
• 3. Agar:
• Vegetable mucilage, sulfuric acid ester of a complex
galactose polysaccharide.
• Non digestable
• Peristalsis after ingestion, so as a laxative
• Medium to grow bacteria

27. .
B-Nitrogenous heteropolysaccharides:
They contain sugar amines and are of two types:
1. Neutral nitrogenous heteropolysaccharides
2. Acidic nitrogenous heteropolysaccharides

28. 1-Neutral nitrogenous heteropolysaccharides
Glycoproteins or mucoproteins:
• They do not contain uronic acids or sulfate groups
(which give acidic characteristics).
• They are formed of a large protein core to which
are attached smaller branched or unbranched
chains of carbohydrate.
• The carbohydrate present include:
Hexoses: mannose, galactose and glucose
Pentoses: xylose and arabinose.
Amino sugars: glucosamine and galactosamine.
Deoxysugars: L-fucose, L-rhamnose and sialic acid.

29. • Glycoproteins have branched oligosaccharide
chains covalently attached to polypeptide
backbone.
• These are present in animals, human, viruses and
bacteria.
• Their carbohydrate content ranges form 4–85% by
weight
• Most of the monosaccharides are found in
glycoproteins. The functions of oligosaccharide
part is:

30. .
• i. It changes the physiochemical properties
[solubility, viscosity, charge and etc.]
• ii. Protects against proteolysis by viruses and
bacteria.
• iii. Affects embryonic development, differentiation
and cell–cell recognition.
• iv. Oligosaccharide chain contains biological
information, which is dependent upon constituent
sugars, their sequence and their conformation.

31. .
• Structure:
• The common core has branched oligosaccharide of
3Man and 2GlcNAc residues.
• Many other sugars may be added to it to form
various glycoproteins.
• Mannose rich oligosaccharides part is replaced by
mixed sugars in some glycoproteins

32. .
Distribution: Glycoproteins are widely distributed in
mammalian tissues. They include:
1. Mucins of epithelium lining of gastrointestinal,
urogenital and respiratory tracts are lubricant and
protective.
2. Cell membranes where they play an important
part in cell-cell attachment.
3. Blood group substances A and B antigens.
4. Mineral and vitamin transporting protein, e.g.,
transferrin.

33. .
5. Immunoglobulins (antibodies), IgG, IgM, IgA….
6. Some hormones, e.g., anterior pituitary
hormones: LH and FSH.
7. Some enzymes such as peptidases and alkaline
phosphatase.
8. Intrinsic factor that is responsible for vitamin B12
absorption.
9. Structural function as a part of collagen of
connective tissue.

34. 2. Acidic nitrogenous heteropolysaccharides
A-Sulfur-free mucopolysaccharides:
• Their sugar units are not sulfates, e.g., hyaluronic
acid.
B- Sulfur-containing mucopolysaccharides:
• Their sugar units are sulfated ,e.g.,chondroiten
sulfate , Heparin

35. STRUCTURE OF GLYCOSAMINOGLYCANS
• Glycosaminoglycans are long, unbranched,
heteropolysaccharide chains generally composed of
a repeating disaccharide unit [acidic sugar-amino
sugar]n
• (glucosamine or
galactosamine which may or
may not be sulphated) and
uronic acid (glucuronic or
Iduronic acid).
• keratan Sulfate – Galactose
rather than an acidic sugar is
present.

36. • The amino sugar is either D-
glucosamine or D-
galactosamine, in which the
amino group is usually
acetylated thus eliminating
its positive charge
• The amino sugar may also be
sulfated on carbon 4 or 6 or
on a nonacetylated nitrogen
• The acidic sugar is either D-
glucuronic acid or its carbon-
5 epimer L-iduronic acid
• (Negative charge)

37. Glycosaminoglycan overview
• Negatively charged heteropolysaccharide chains.
• Associated with a small amount of protein, forming
proteoglycans (95% CHO)
• Bind large amounts of water(special ability)
producing the gel-like matrix -- ground substance
• EXTRACELLULAR MATRIX (ECM):
• Glycosaminoglycans, Fibrous structural proteins eg.
(Collagen, Elastin) and Adhesive proteins
(fibronectin)

38. .
• GLYCOSAMINOGLYCANS
Flexible support for the ECM
Interacting with the structural and adhesive
proteins
Molecular sieve
Viscous, Lubricating properties of mucous
secretions (original name: mucopolysaccharides)

39. .
• ii. Disaccharide part is covalently attached to a
protein molecule and the compound formed is
called proteoglycan.
• iii. They act as packing material in structural
elements of tissues, bones, elastin, and collagen.
• vi. They absorb large amount of water and act as
lubricants.

40. .
• v. Proteoglycan from cartilage has keratan–SO4 and
chondrotin–SO4 chains, which are covalently linked
to a core protein.
• Some 140 core proteins are non–covalently linked
at an interval of 300Å to a long filament of
hyaluronate supported by small link proteins.
• Proteoglycans from different sources have different
structures.

41. .
• Resilience of
glycosaminoglycans
large number of negative charges,
repel each other
they “slide” past each other,.
produces the “slippery” consistency
of mucous secretions and synovial
fluid.
water is “squeezed out,” and the
GAGs are forced to occupy a smaller
volume.
GAGs spring back to their original,
hydrated volume because of the
repulsion of their negative charges.
resilience of synovial fluid and the
vitreous humor of the eye

42. C. Proteoglycans
• Proteoglycans are found in the ECM and on the
outer surface of cells.
• 1. Structure of proteoglycan monomers:
• A proteoglycan monomer found in cartilage consists
of a core protein to which up to 100 linear chains of
GAGs are covalently attached.
• These chains, which may each be composed of up
to 200 disaccharide units, extend out from the core
protein and remain separated from each other
because of charge repulsion. The resulting structure
resembles a “bottle brush”

43. .
• GAG-Protein linkage:
• This covalent linkage
is most commonly
through a trihexoside.
(galactose-galactose-
xylose)
• Aggregate formation:
Many proteoglycan monomers associate with one
molecule of hyaluronic acid to form proteoglycan
aggregates. The association is not covalent but occurs
primarily through ionic interactions between the core
protein and the hyaluronic acid.

44. .
• .

45. Proteoglycans are glycosaminoglycans that are
covalently linked to serine residues of specific
core proteins.
The glycosaminoglycan chain is synthesized by
sequential addition of sugar residues to the core
protein.
heparan sulfate
glycosaminoglycan
cytosol
core
protein
transmembrane
-helix

46. .
• Functions in Body
• Proteoglycans in extra-cellular matrix are criss
crossed by fibrous matrix proteins (collagen,
elastin, fibronectin).. Strength
• Tisue organizers, development of specialised
tissues, mediate activities of various growth factors.
• Regulate extracellular assembly of collagen fibres
• Major component of cartilage –strength

47. .
• Heparan sulphate binds extracellular ligands—
interaction with specific receptors on cell surface
• Fibronectin can bind fibrin, heparan sulfate collagen
ad integrins --- information transfer
• Aggrecan –interacts with collagen – strength
• Special pattern of sulfated and non-sulfated sugar
units – recognition by ligands
• Carboxyl and sulfated groups – negative charge

48. .
• Repel each other – slippery and vicious
• Found in cartilage, skin, blood vessels, cornea,
tendons, ligaments, loose CT, heart valves.
• All GAGs (except hyaluronic acid), occur in
combination with extracellular proteins through
covalent linkages---proteoglycan monomers

49. .
Hyaluronic acid: -
• It is formed of -D-N-acetyl glucosamine linked to
-D-glucuronic acid by alternating -1,3- and -1,4-
glycosidic linkages.
O
H
H
H
OH
H
OH
CO
OH O
H
OH H
H
NH-
CO-
CH
3
H
CH
2OH
O
O 1 3
1
4
O
H
H
n
-Glucuronicacid -N-acetyl-Glucosamine
Hyaluronicacid

51. The glycosidic linkages are (13) & (14).
Up to 50,000 repeats of these repeating units.
H O
H
H
OH
H
OH
COO
H
H O
OH H
H
NHCOCH
3
H
CH2OH
H
O
O
D-glucuronate
O
1
2
3
4
5
6
1
2
3
4
5
6
N-acetyl-D-glucosamine
hyaluronate

52. .
Biochemical importance:
1. The molecule is coiled and entwined making a
very firm gel which prevents bacterial invasion
of the skin. High viscosity
2. It is present in connective tissue matrix,
vitreous humor of the eye, in the skin, synovial
fluid, around the ovum, and in the umbilical
cord to preserve the full-form of these
structures.
3. It acts as a cementing substance between cells
and as a lubricating material of joints.

53. .
4. Hyaluronic acid imbibes water and forms a
incompressible substance due to the presence
of several OH groups which creates negative
charges causing repulsion between
carbohydrate units enabling the molecule to
perform its function as lubrication in joint
synovial fluids an.

54. .
• Hyaluronidase Enzyme or Spreading factor:
• It is the enzyme that hydrolyzes hyaluronic acid.
• It is present in sperms to help penetration of the
ovum and fertilization.
• It is present in some virulent strains of bacteria
that are able spread through infected wounds.
• It is used in medicine to treat fibrosis and to
dissolve mucus.

55. .
• B. Sulfur-containing mucopolysaccharides
1-Chondroitin sulfate: it is of three types as follows:
• Chondroitin sulfate A:
• It is formed of -N-acetyl-galactosamine-4-sulfate
and -glucuronic acid linked by alternating -1,3-
and -1,4-glycosidic linkages.
O
H
H
H
OH
H
OH
COOH O
HO3SO
H H
H
NH-CO-CH3
H
CH2OH
O
O 1 3
1
4
O
H
H
n
-Glucuronic acid -N-acetyl-Galactosamine, 4-sulfate
Chondroitin Sulfate A

56. .
• Chondroitin sulfate B:
• It is formed of -N-acetyl galactosamine-4-
sulfate and -L-iduronic acid linked by
alternating -1,3- and -1,4-glycosidic linkages.
• L-iduronic acid is the C5 epimer of D-glucuronic
acid, i.e., COOH group at C5 is inside the ring,
O
H
H
H
OH
H
OH
H O
HO3SO
H H
H
NH-CO-CH3
H
CH2OH
O
O 1 3
1
4
O
H
COOH
n
-L-Iduronic acid -N-acetyl-Galactosamine, 4-sulfate
Chondroitin Sulfate B

57. .
• Chondroitin sulfate C:
• It is formed of -N-acetyl galactosamine-6-
sulfate and -glucuronic acid linked by
alternating -1,3- and -1,4-glycosidic linkages.
• Present in cornea of the eye, tendons,
ligaments, bones, cartilage and connective
tissue matrix.
• They absorb water, form incompressible
substances by means of their ionizable OH and
sulfate groups, creating negative charges
leading to repulsion between the molecules.

58. …..
O
H
H
H
OH
H
OH
COOH O
OH
H H
H
NH-CO-CH3
H
CH2OSO3H
O
O 1 3
1
4
O
Chondroitin Sulfate C
H
H
n
-Glucuronic acid -N-acetyl-Galactosamine, 6-sulfate

60. .
2. Heparin:
Structure: It is formed of a long repeat of sulfated
-glucosamine and sulfated -L-iduronic acid
linked by alternating - and -1,4-glycosidic
linkages, synthesized on a core protein.
Source: It is produced by mast cells (kidney, lung,
liver skin).
O
H H
H
NH-SO3H
H
OH
CH2OSO3H
H
O
H
H
H
OSO3H
H
OH
H
COOH
O
O
O
n

Heparin
1 4 1
4
-Glucosamine, N- and 6-sulfated -L-Iduronic acid, 2-sulfate

61. ..

62. .
• Function:
1. It is an anticoagulant and prevents intravascular
clotting. It interferes with the activated clotting
factors (thrombin, IX, X, XI and XII) in coagulation,
through activation of antithrombin III that inhibits
the intrinsic pathway of blood clotting. Therefore,
it is used in cases of increased coagulability, e.g.,
cardiac ischemia or deep venous thrombosis.
2. It binds activates lipoprotein lipase enzyme (the
plasma clearing factor) to clear the turbid plasma
from the absorbed lipids after meals.

63. 3. It regulates the action of the heparin-binding
growth factors.
4. It has a structural role in extracellular matrix. It
affects cell-cell and cell-matrix interaction to
modulate development, cell proliferation,
apoptosis and differentiation.
5. Large number of sulfate groups ---highest
negative charge density !!
.

64. III. Kertan–SO4–I and II:
• The repeating unit is [Gal ……. GlcNAc–SO4]n.
• Sulphate is present at position 6 of GlcNAc or
sometimes linked to Gal.
• Type I predominates in cornea and type II along
with chondroitin–SO4 is attached to hyaluronic
acid in loose connective tissues.
• Present in cornea, cartilage, bone, and dead cells
horny structures like horns, hoofs, hair, nails,
claws.

65. .

66. V. Dermatan–SO4:
• The repeating unit is composed of [IdUA – GalNAc]
n –[GlcUA – GalNAc]n.
• It has both IdUA and GlcUA attached to GalNAc..
• Pliability of skin
• Blood vessels and heart valves.

68. Mucopolysaccharidoses
• Mucopolysaccharidoses is a genetic defect due to
the deficiency of particular Iysosomal enzymes that
degrade particular GAGs.
• This leads to the accumulation of GAGs in various
tissues. There occurs mental retardation.
• The specific GAGs are also excreted in urine.
• In arthritis, Proteoglycans may act as an
autoantigen and contribute its effects to the
pathology.

69. Important Monosaccharides
• D-Glucose is the most common monosaccharide
- Primary fuel for our cells, required for many
tissues
- Main sources are fruits, vegetables, corn syrup
and honey
- Blood glucose is maintained within a fairly small
range
- Some glucose is stored as glycogen, excess is
stored as fat
During urine formation, glucose is nearly completely
reabsorbed and only traces escape in urine

70. ……
• Its normal value in blood, at random ranges from
65–110 mg/dL but in abnormal conditions known
as Diabetes Mellitus, its quantity is elevated to
several hundred mg/dl.
• It is the fuel for brain and provides energy to brain
and other tissue
• The estimation of glucose in various biological
fluids is performed for diagnostic purposes.

71. ..
• Glucose is converted to other sugars and their
derivatives which are then used for the synthesis of
heteropolysaccharides, glycolipids etc.
• The other sugars of specific functions are formed
from glucose and are incorporated into
heteroplysaccharides of structure material.

72. .
• D-Fructose is the sweetest carbohydrate,
is levulose.
- Converted by an enzyme into glucose for
respiration
- Main sources are fruits and honey
- hydrolysis of sucrose,
• In the seminal fluid, it is present in appreciable
amounts

73. ..
D–Galactose:
• It is an aldohexose, dextrorotatory, mutarotation.
• It is a part of milk sugar, lactose.
• Galactose in the form of galactosamine is a part of
sulphonated mucopolysacharide such as
chondroitin [chondroitin sulphuric acid and
protein].
• Galactose is also a component of
galactocerebrosides present in brain.
• It is an epimer of glucose and differs in
configuration around ‘C’ No.4 of glucose.

74. ..
• In liver, galactose is converted into glucose.
• In a disease known as Galactosemia, the body
cannot utilize it and galactose increases in the blood
and aqueous humor.
• Galactose in the lens of the eye is converted to
galactitol and forms cataract.
• Galactosemia in children is treated by feeding them
galactose free diet.
• The galactose necessary for the biosynthesis of cell
membrane, cerebrosides, glycoproteins etc. is
formed from glucose.

75. ..
D–Mannose:
• Aldohexose and is an epimer of glucose, differing in
configuration around C atom No. 2 of glucose.
• Mannose is a carbohydrate component of albumin,
globulins and mucoids.
• Mannose is richly present in the common core of
glycoproteins.
• Its derivative IdUA is a component of heparin.

76. CARBOHYDRATES OCCUR IN CELL
MEMBRANES & IN LIPOPROTEINS
• In addition to the lipid of cell membranes,
approximately 5% is carbohydrate in glycoproteins
and glycolipids.
• Carbohydrates are also present in apo B of
lipoproteins.
• They are present on the outer surface of the plasma
membrane (the glycocalyx).
• Glycophorin is a major integral membrane
glycoprotein of human erythrocytes and spans the
lipid membrane.

77. ..