CarbohydratesTehran University of Medical

Sciences (TUMS)

Mahdi Aminian, Ph.DDepartment of Biochemistry

Mehr 92

1) Monosaccharides

- Simple

- Derivatives

2) Oligosaccharides

3) Polysaccharides

Saccharides

•Disaccharides are formed by a condensation reaction between

two monosaccharides.

•The covalent linkage is called an O-glycosidic bond and

represents the formation of an acetal from a hemiacetal and an

alcohol.

Disaccharides

•Glucose on the right:

Reducing end of the disaccharide molecule because it can participate

in a reduction reaction.

•Glucose on the left:

Nonreducing end because the C-1 carbon is part of the α1-4 linkage

and cannot form the open chain structure in a reduction reaction.

•Maltose contains one reducing end and called a reducing sugar.

•Disaccharide name:

listing the nonreducing monosaccharide on the left, followed by the

glycosidic linkage between the two monosaccharides, and then the

monosaccharide on the right.

Reducing:

Maltose

Lactose

Non-reducing:

Trehalose

Sucrose

Disaccharides

Maltose

Lactose

Sucrose

Trehalose

Disaccharides

1-Monosaccharides

- Simple

- Derivatives

2-Oligosaccharides

-Reducing: Maltose, Lactose

-Non-reducing: Trehalose, Sucrose

3-Polysaccharides

Saccharides

A) Pure Polysaccharides

a) Homo Polysaccharides

Structural & Storage (Cellulose, Chitin & Glycogen, Inulin)

Or

Linear & Branched (Amylose, Inulin & Glycogen, Amylopectin)

b) Hetero Polysaccharides

Hyaluronic acid, Chondroitin sulfate, Heparin

B) Complex Polysaccharides

Classifications of Polysaccharides

•The chief constituent of the framework of plants.

•Insoluble.

•Important source of “bulk” in the diet.

•β-D-glucopyranose.

•Linked by β(1 → 4) bonds.

•Cannot be digested by mammals (absence of β linkage hydrolyzing

enzyme).

•Microorganisms can hydrolyze the β linkage.

Cellulose

•Structural polysaccharide in the exoskeleton of crustaceans and

insects.

•Consists of N-acetylglucosamine units joined by β(1 →4)-

glycosidic linkages.

•Chitinase of microorganisms.

Chitin

Chitin

Similar to cellulose, but C2s are N-acetyl

•Storage polysaccharide in plants.

•Homopolymer of glucose (glucosan or glucan)

•α-glucosidic chain

•The two main constituents:

Amylose (20%)

Amylopectin (80)

Starch

Amylose, a linear polysaccharide containing about ~100

glucose units linked by α(1-4) glycosidic bonds.

Amylopectin, a branched polysaccharide containing ~100,000

glucose units connected by α1-4 and α1-6 glycosidic bonds.

Amylose can form stable left-handed helical structures as a result

of intramolecular hydrogen bonding.

α-amylase:

Cleaves α(1-4) glycosidic bonds.

Amylose

Amylopectin

•Storage polysaccharide in animals.

•Up to 106 glucose units per granule.

•α-D-glucopyranose

α(1 → 4)-glucosidic linkage

α(1 → 6)-glucosidic bonds

•Amylopectin:

a branch point about once every 25 glucose units.

•Glycogen:

a branch point every 10 glucose units.

•More branch points there are, the more ends that are available for

glucose retrieval and storage.

Glycogen

Glycogen

Inulin:

-A polysaccharide of fructose (fructosan) found in roots of some

plants.

-It is readily soluble in water and is used to determine the

glomerular filtration rate.

Dextrins:

Intermediates in the hydrolysis of starch.

Heteropolysacharides

Glycosaminoglycans

(mucopolysaccharides)

An important class of polysaccharides in connective tissue and

the extracellular matrix.

Hyaluronic acid, Chondroitin sulfate, Heparin

These unbranched polysaccharide chains consists of repeating

disaccharide units made up of modified monosaccharides.

Amino sugars & Uronic acids

Proteoglycan:

-Attachment of these chains to a protein molecule.

Glycosaminoglycans

Hyaluronic acid is highly hydrated & lubricant in joints

Hyaluronic Acid

Chondroitin Sulfate

Heparin

15-90

Heparin

Heparin is an example of highly sulfated glycosaminoglycan that

is present in granules of special cells in the circulatory system

called mast cells.

Release of heparin from mast cells prevents blood clotting by the

binding of the negatively-charged heparin to proteins that initiate

the clotting cascade.

Purified heparin is used as an anti-coagulant in clinical laboratories

that need to store and process blood products.

Heparin

A) Pure Polysaccharides

a) Homo Polysaccharides

Sturctural & Storage (Cellulose, Chitin & Glycogen, Inulin)

Or

Linear & Branched (Amylose, Inulin & Glycogen, Amylopectin)

b) Hetero Polysaccharides

Hyaluronic acid, Chondroitin sulfate, Heparin

B) Complex Polysaccharides

a) Polysaccharides + Proteins

b) Polysaccharides + Lipid

Classifications of Polysaccharides

1- Polysaccharides + Proteins:

a) Proteoglycane (Extra cellular matrix) & Peptidoglycane(Bacterial cell wall)

b) Glycoprotein (ABO blood group, Serum Glycoproteins)

2- Polysaccharides + Lipids:

a) Lipopolysccharide (Gram negative bacterial cell wall)

b) Glycolipid (Receptors for bacterial toxins)

Complex Polysaccharides

Proteoglycane

Bacterial Peptidoglycans

The sugars : yellow

The tetrapeptides: red

The pentaglycine : blue

Peptidoglycan

Transpeptidases are required

for peptidoglycan synthesis

•Alexander Fleming discovered the antibiotic penicillin in 1929

•Penicillin inhibits bacterial enzymes called transpeptidases that are

required for peptidoglycan synthesis

•Some bacteria are resistant to penicillin because they produce an

enzyme called β-lactamase that hydrolyzes the β lactam ring in

penicillin to inactivate it.

•This type of penicillin-resistance has been overcome by developing

synthetic compounds such as methicillin that block transpeptidase

activity without being substrates for β-lactamase.

•A methicillin-resistant strain of S. aureus,called MRSA, has emerged

that expresses a variant form of the transpeptidase enzyme.

Infection of methicillin-resistant S. aureus

They are proteins containing branched or unbranched oligosaccharide

chains.

Oligosaccharide modification at endoplasmic reticulum.

Many types of membrane-bound proteins & most secreted proteins.

Serum Glycoproteins

Protein glycosylation :

Highly specific and requires of glycosyltransferases enzymes.

Immunological incompatibility:

Genetic differences in the expression and activity of Glycosyltransferases.

Glycoproteins (mucoproteins)

Human CD2 protein(surface of T cells)

Blood Groups

Glycoproteins:O-linked oligosaccharides

N-linked oligosaccharides

Glycolipids (Crebroside, Ganglioside)

Glycolipids & Lipopolysaccharides

1-Monosaccharides

A) Simple B) Derivatives

2-Oligosaccharides

A) Reducing (Maltose, Lactose) B) Non-reducing (Trehalose, Sucrose)

3-Polysaccharides

A) Pure Polysaccharides:

a) Homo Polysaccharides

(Sturctural & Storage ) or (Linear & Branched)

b) Hetero Polysaccharides

(Hyaluronic acid, Chondroitin sulfate, Heparin)

B) Complex Polysaccharides:

a) Polysaccharides + Proteins

1) Proteoglycane (Extra cellular matrix) & Peptidoglycane (Bacterial cell wall)

2) Glycoprotein (ABO blood group, Serum Glycoproteins)

b) Polysaccharides + Lipid

1) Lipopolysccharide (Gram negative bacterial cell wall)

2) Glycolipid (Receptors for bacterial toxins)

Classification of Saccharides