2. Significant Carbohydrates

3. Learning Objectives To identify some of the important carbohydrates
To describe some of the characteristics of these individual sugars
To understand the importance of individual sugars
To explain the clinical significance (if any) of these carbohydrates

4. Monosaccharides (Trioses)
Aldotrioses (D & L-glyceraldehyde)
Simplest and smallest sugar
One asymmetric carbon (02 isomers)
Gly-3-P is a metabolite of glycolysis & HMP-Shunt
Precursor of glycerol (required for the synthesis of TAGs)
Ketotrioses (Dihydroxy-acetone)
No asymmetric carbon (no isomer)
A metabolite of glycolysis
Can be converted into glyceraldehyde & glycerol

5. Monosaccharides (Tetroses)
Aldotetroses (e.g. erythrose)
Two asymmetric carbons (4 isomers)
A metabolite of HMP-Shunt
Ketotetroses (e.g. erythrulose)
One asymmetric carbon (2 isomers)

6. Monosaccharides (Pentoses)
Aldoses
Ketoses

7. Biochemical importance
Monosaccharides (Pentoses)
Sugar
Where found
Biochemical importance
D-Ribose
Nucleic acids,
Nucleotides
Component of nucleic acids (RNA) and coenzymes e.g. ATP, NAD, NADP, flavoproteins.
Ribose phosphates are intermediates in pentose phosphate pathway
D-Ribulose
Formed in
metabolic
processes
Ribulose phosphate is an intermediate in
pentose phosphate pathway
D-Arabinose
Gum Arabic, plum and cherry gums
Constituent of Glycoproteins

8. Clinical significance
Monosaccharides (Pentoses)
Sugar
Where found
Biochemical
importance
Clinical significance
D-Xylose
Wood gums,
proteoglycans
glycosaminoglycans
Constituent of
glycoproteins
D-Lyxose
Heart muscle
A constituent of a
lyxoflavin isolated
from human heart
muscle.
L-Xylulose
Intermediate in
uronic acid pathway
Found in urine
in essential
pentosuria

9. Monosaccharides (Hexoses)
Aldoses

10. Monosaccharides (Hexoses)
Ketoses

11. Monosaccharides (Hexoses)
Sugar
Source
Importance
Clinical significance
D-Glucose
(Dextrose)
Grape sugar
Blood sugar
(Aldose)
Fruit juices,
Hydrolysis of
starch
cane sugar, maltose &
lactose
Stored as glycogen
The sugar of the body.
The sugar carried by the blood, and the principal one used by the tissues, RBCs, brain cells
Acts as immediate energy source for cellular functions like muscle contraction, nerve transmission and tissue repair
Can be converted into other sugars or derivatives required for GAGs & Glycolipids
Present in the urine
(glycosuria) in diabetes mellitus
owing to raised
blood glucose
(hyperglycemia)

12. Clinical significance
Monosaccharides (Hexoses)
Sugar
Source
Importance
Clinical significance
D-Fructose
Fruit Sugar
Levulose
Keto sugar
Sweeter
than Glu
Fruit juices, Honey
Hydrolysis of
cane sugar & inulin
Seminal fluid is rich in Fructose
Can be
changed to
glucose in the
liver and so
used in the
body
Herediatary
Fructose intolerance
leads to fructose
accumulation and
hypoglycemia
D-Mannose
Aldo- Sugar
Epimer of
glucose
Hydrolysis of
plant mannans
and gums
A constituent of many Glycoproteins
When oxidized
gives IdUA-a component of Heparin

13. Clinical significance
Monosaccharides (Hexoses)
Sugar
Source
Importance
Clinical significance
D-Galactose
Aldo- Sugar
Epimer of
Glucose
Less sweet than Glu
Hydrolysis of
Milk sugar
Galactolipids
Glycoproteins
Can be changed
to glucose in the
liver and then
metabolized.
Synthesized in
the mammary gland to make
the lactose of milk.
A constituent
of glycolipids and
Failure to
metabolize
leads to
galactosemia
and cataract
(Galactitol)

14. Clinical significance
Disaccharides
Sugar
Source
Clinical significance
Maltose
Glc – Glc
 14
Reducing
Digestion by amylase or hydrolysis of starch cereals and malt.
Also known as
Malt sugar
Lactose
Milk sugar
Gal – Glc
 14
Reducing
Milk,
May occur in urine during
pregnancy and lactation
In lactase deficiency
malabsorption leads to
diarrhea and
flatulence.

15. Clinical significance
Disaccharides
Sugar
Source
Clinical significance
Sucrose
Glc – Fru
 12
Non-reducing
Cane and beet sugar.
pineapple, carrot roots.
Also known as Invert sugar (d → l)
In sucrase deficiency,
malabsorption leads to
diarrhea and
flatulence.
Trehalose
Glc – Glc
 11
Non-reducing
Fungi and yeasts.
The major sugar of insect
hemolymph.

16. Disaccharides Lactulose (Gal + Frc)
Used in the treatment of some chronic liver diseases associated with hyper-ammonemia
Lactitol (galactosido-sorbitol)
Also used in the treatment of some chronic liver diseases

17. Clinical significance
Disaccharides
Sugar
Source
Clinical significance
Cellobiose
Glc – Glc
 14
Reducing
Plants (cellulose)
Gentiobiose
Glc – Glc
 16
Reducing
Plants
Constituent of plant glycosides and some polysaccharides

18. Oligosaccharides (contain same or different
Oligosaccharides (contain same or different monosaccharides or their derivatives)
Trisaccharides:
raffinose (glucose, galactose and fructose)
Tetrasaccharides:
stachyose (2 galactoses, glucose and fructose)
Pentasaccharides:
verbascose (3 galactoses, glucose and fructose)
Hexasaccharides
ajugose (4 galactoses, glucose and fructose)

19. Oligosaccharides OCCURRENCE:
Oligosaccharide chains are found as part of glycoproteins ( & glycolipids ) attached through
O2 of serine or threonine (O – glycosidic)
N of asparagine (N – glycosidic) or
Glycosyl-phosphatidyl-inositol (GPI) linkage

20. Oligosaccharides
Glycoproteins containing oligosaccharide chains include
Integral membrane proteins,
Receptors
Hormones and
Other proteins (like antibodies, clotting factors)

21. Functions of the Oligosaccharide chains of glycoproteins
Modulate physicochemical properties, e.g. solubility,
viscosity, charge, conformation, denaturation, and binding sites for bacteria and viruses.
Involved in biologic activity e.g. of human chorionic gonadotropin (hCG)
Affect membrane functions like transport across membrane, intracellular migration, sorting and secretion
Affect embryonic development
Protect against proteolysis,