Saccharides

(Structure and biological function)

Ďuračková Zdeňka

Departemnt of Medical chemistry, Biochemistry

and Clinical Biochemistry,

Komenius University

Medical Faculty

Bratislava

Importance

• Source of energy

glucose, glycogen, starch

• Structural function

connective tissue, membranes

nucleic acid

• Recognitive function

cytoplasmic membranes

receptors

Monosaccharides

(1 unit)

Polysaccharides

(more than 10 units)

Oligosaccharides

(2 – 10)

Saccharides

Monosaccharides

• Triózy – C3 - Trioses

• Tetrózy – C4 - Tetroses

• Pentózy – C5 - Pentoses

• Hexózy – C6 - Hexoses

• Polyhydroxyaldehydes

- OH, - CHO

• Polyhydroxyketons

- OH, >C=O

Saccharides - Sacharidy

CnH2nOn

• Trioses C3H6O3

• Tetroses C4H8O4

• Pentoses C5H10O5

• Hexoses C6H12O6

Properties of monosaccharides

• Soluble in water

Insoluble in organic solvents and lipids

• Nonelectrolytes

They do not disociate in water

• Sweet taste

Functional isomers

Aldose Ketose

C3H6O3

Epimers

• Different possition of one secondary -OH

C H O

O H

H O

O H

O H

C H2O H

C H O

H O

O H

O H

C H2O H

H O

C H O

O H

H O

H O

O H

C H2O H

C H O

O H

O H

C H2O H

O H

C H O

O H

C H2O H

O H

H O

D-glucose D-manose D-galactose

C2 epimer

C4 epimer

D-ribose D-arabinose

Optical isomers – enanthiomers – stereoisomers

*

Enanthiomers (D-,L- isomers) C6H12O6

Difference in the

possition of all

secondary

- OH groups

Responsibility for D- a L-classification =>

The last

asymetric carbon

*

*

*

*

Cyclic monosaccharides = hemiacetals

H

R - C = O + HO – R R – C - OH

O – R

H

HemiacetalReaction of hemiacetal formation

Aldehyde Alcohol

Cyclic monosaccharides = hemiacetals

O

OH

OH

O

H-C=O

H-C-OH

HO-C-H

H-C-OH

H-C-OH

CH2-OH

Tollens projection

Fischer projection

Anomers

+ 52,7

+ 112 + 18,7

Anomers formation from fructose

and glucose

Important monosaccharides

D – Glucose

• the most extended in naturebuilding unit of starch, glycogene and cellulose

• concentration in blood 3,3-5,5mmol/l

regulation by insulin and glucagon

patolog.state: diabetes mellitus

• source of energy (especially for brain and erythrocytes)

C

C

C

C

C

CH2OH

OH

OHH

HHO

OHH

OHH

D - galactose

• epimer of glucose – different configuration at C-4

• linked

in lactose (disaccharid)

building part of glykoproteins, glykolipids

C

OH

CH OH

C HHO

C HHO

C OHH

CH2OH

D – fructose

• the most extended ketose

• free – honey

• linked in saccharose

(disacharide)

C

C

C

C

O

HHO

OHH

OHH

CH2

CH2OH

OH

C

C

C

C

O

HHO

OHH O

H

H

CH2

CH2OH

OH

D-alpha-fructose (-)

D - ribose and D - 2 - deoxyribose

• pentoses

• building units of nucleic acids

O

HH

H

H

OH

H

OHH2CHO

2-deoxyribosa

C

C

C

C

CH2OH

OHH

OHH

OHH

OH

C

C

C

C

CH2OH

HH

OHH

OHH

OH

Ribose 2-deoxyribose

Phosphate ester formation

R OH + HO P OH

O

OH

R O P OH

O

OH

+ H2O

Alcohol Phosphoric acid Phosphate ester

Phosphate esters of monosaccharides

Cori’s ester Robison’s ester

Neuberg’s ester

Aminosaccharides

Sialic acids

- NH2 substitution:

•acetyl

•glykolyl

-OH substitution:

•acetyl

•laktyl

•sulfát

•fosfát

Enolisation

Reduction of

monosaccharides

C

CH2

OHOH

OHOH

OH

H O

CH2

OHOH

OHOH

CH2 OH

OH

red.

(+ 2 H)

CH2

OOH

OHOH

CH2 OH

OH CH2

OHOH

OHOH

CH2 OH

OH

D- glukóza D- glucitol

D- manitolD- fruktóza

red.

red.

(+ 2 H)

(+ 2 H)

HO

HO

HO

HOHO

Oxidation of glucose

Glucuronic acid Glucaric acid

Gluconic acid

Glucose

Uronic acid Aldonic acid Aldaric acid

1

1

6

6

Oxidation of glucose

Glucuronic acid Glucaric acid

Gluconic acid

Glucose

Uronic acid Aldonic acid Aldaric acid

X

X

1

1

6

6

Oxidation of UDP-glucose to UDP-glucuronic acid

X

The function of glucuronic acid

• Detoxication of aromatic compounds

• Substrate for ascorbic acid synthesis

Biological functions of ascorbic acid

• Co-factor of enzymes – hydroxylases

• Reductant (Fe(III) Fe(II), Cu(II) Cu(I))

• Reduction of nitroso-compounds to nontoxic form

• Scavenger of superoxide, .OH, R

.

Non-enzymic

glycation of

proteins

C

CH2

OHOH

OHOH

OH

H O

D- glukóza

H2N proteín+

CH2

OHOH

OHOH

OH

CH N proteín

aldimín

(Schiffova zásada)

CH2

OOH

OHOH

OH

CH2 NH proteín

ketoamín

(fruktózamín)

- H2OHO

HO

HO

Glycosides formation

Sach-OH HO-Sach+ Sach-O-Sach

hologlycosid

Sach-OH + HO-R Sach-O-R

O -heteroglycosid

Sach-OH + HN< Sach-N<

N -heteroglycosid

Important disaccharides

Maltose

• malt, enzymatic hydrolysis of starch in intestine

• 2 molecules of glucose - -1,4 glycosidic bond

• free hemiacel group is present – reducing disaccharide

- maltosa

Lactose

• „milk saccharid“

• galactose and glucose, -1,4 glycosidic bond

• milk : cow 4-6%

women 6%

• less sweet than saccharose

• free hemiacel group is present –

reducing disaccharide

Saccharose

• „beet sugar, cane sugar“

• glucose and fructose, – 2,1 glycosidic bond

•no free hemiacetal group is present – non-reducing

disaccharid

Cellobiose

• building unit of cellulose

• 2 molecules of glucose, - 1,4 glycosidic bond

- celobiosa

Polysaccharides

• Homopolysaccharides

(one kind of monomeric unit)

• Heteropolysaccharides

(two or more different monomeric units)

Homopolysaccharides

• Polyglucan (starch, glycogen)

• Polygalactan (agar)

• Polyfructan (inuline)

Starch

• lat. amylum, angl. starch, greec amylo

• storage polysaccharides of plants

• The main sorce of energy

• Formed from D-glucoses

• In water at higher temperature coloidal solution

• Different numbers of monosaccharid units

The composition of starch

Amylose• 20-30 %

• -1,4 bonds

• linear (helix)

• Soluble in water

• Amylase is cleaved to

maltose

Amylopectine

• 70-80 %

• -1,4 + -1,6 bonds

• branching

• Insoluble in water

• Amylase is cleved in

maltose + dextrins

Amylose

O

OO

HO

OH

O

O

HO

OH

O

H

H O

OO

HO

OH

O

O

HO

OHH

H

14

Amylopectine

O

OO

HO

OH

O

O

HO

OH

O

H

H

O

OO

HO

OH

O

O

HO

OH

O

H

H O

OO

HO

O

O

HO

OHH

H

14

1

6

Glycogen

• Storage polysaccharid in animals

• Similar as amylopectine, branching is more

frequent

• Bonds -1,4 + -1,6

• The accurrence in food is low

(liver, horse meet)

Branching in glycogene

····

· · ·

α-1,4

α-1,6

Cellulose

• The most expanded polysaccharide in plants

• composed from D-glucose,

• bonds -1,4

• linear chains layed paralel and fixed with

hydrogen bonds,

• The consequence – strenght and water insolubility

Cellulose

O

OH

HOO

OH

O

OH

HO O

OH

O

OH

HOO

OH

O

OH

HO

OH

1

4

ß

HETEROPOLYSACCHARIDES

(heteroglykans)

(derivSach-O-derivSach)n

Examples of derivatives of

monosaccharides present in

heteropolysaccharides

Glucosamine

D-Glucuronic acid

L-Iduronic acid

HETEROPOLYSACCHARIDES

(Mucopolysaccharides)

2 different monomers

(6 classes)

Chondroitinsulphate (GUA + GAL-NAc-SO4)n

Darmatansulphate (IdUA + GAL-NAc-SO4)n

Keratansulphate (GAL + GNAc-SO4)n

Heparinsulphate (IdUA-SO3H + GNAc -SO4)n

Heparine (GUA + GNAc-SO4)n

Hyaluronate (GUA + GNAc)

(no sulphate)

Glykolipids

Proteoglycans

Glykoproteins

Glycoconjugates

Basic glycosaminoglycan is

hyaluronic acid

Glucuronic acid +

N-acetylglucosamine

1934 - Karl Meyer – from cows‘ eyes - in an

ophthalmology laboratory at Colombia

University

1942 - Endre Balazs - from rooster combs –

HA had been injected as a serum into the

arthritic knees

Basic disaccharide

Structure of hyaluronic acid (HA)

1

4OO

OH

HO O

O

NH

O

OH

HO

COCH3

COO

13

COOO

OH

HO O

In human body – 15 g of HA

One third is metabolised daily (degradated and

synthetised)

Hyaluronan has variable molecular weight

Occurence of HA in human body

In the skin

Synovial

fluid

HK – connective tissue

in the gum

In joint In tooth

Occurence of HA in human body

Heparin

• Antiagregation agent of blood in vivo + in vitro

• From animal organs is prepared

• Prevention and treatment of thrombosis, after IM,

during surgery performance, etc. = antithrombic

effect

• Preparation of noncoagulated blood for

laboratory and transfusion use = anticoaguland

(Glucuronic acid + NacetylGlucose-sulphate)

Glycoconjugates

Saccharide unit and non-saccharide unit

linked together

Sacharid OH + HO R

Glycoconjugates

Glycoconjugates

• Glycolipids (saccharid unit + sphingosine)

• Proteoglycans (saccharid unit + protein)

• Glycoproteins (saccharid unit + protein)

Proteoglycans

• contains neer to 95% saccharide units

• D-conformation (except: L-iduronic

acid, L-arabinose, etc)

• H2SO4 linked in high amount

• polyanionic character

• high viskosity – biological lubricant

• high elasticity

• influence of water and ionic equillibrium

• stabilizing and retaining function

Importance of proteoglycans

• Part of connective tissues (bons, gristle, skin, cornea,

venous)

• Water is absorbed - gel (responsible - sulphate and

glucuronic acid)

• Gristel (chrupavka) - colagen repleted by poteoglycans,

pressure stability

Thank you

for your attention .............