1

• Lubert Stryer - Biochemistry

• Lehninger- Principles of Biochemistry

• Harper's -Illustrated Biochemistry

References

• Text Book of Biochemistry with clinical correlation, T M. Devlin

بیوشیمی پزشکی، هیئت مولفان ، •دانشگاه علوم پزشکی تهران، انتشارات

آییژ، دو جلد

CarbohydratesCarbohydrates

General characteristicsGeneral characteristics

Compounds composed of C, H, and O

(CH2O)n when n = 5 then C5H10O5

Not all carbohydrates have this empirical formula: Deoxysugars, Aminosugars

Carbohydrates are the most abundant compounds found in nature (cellulose: 100 billion tons annually)

General characteristicsGeneral characteristicsMost carbohydrates are found naturally in bound

form rather than as simple sugars (Glycoconjugates) Polysaccharides (starch, cellulose, inulin, gums),

Mucopolysaccharides (hyaluronic acid)

Glycoproteins and proteoglycans (hormones, blood group substances, antibodies)

Glycolipids (cerebrosides, gangliosides)

Nucleic acids (Ribose and desoxyribose)

FunctionsFunctions

Sources of energy (Glucose, Fructose,..)

Intermediates in the biosynthesis of other basic biochemical entities (Fats and proteins)

Form structural tissues in plants and in microorganisms (cellulose, lignin, murein)

Participate in cell-cell recognition, Cell-cell adhesion

Classification of carbohydratesClassification of carbohydrates

Monosaccharides (monoses or glycoses)

Oligosaccharides (condensation products of two to ten monosaccharides)

Di, tri, tetra, penta, up to 9 or 10 Most important are the disaccharides

Polysaccharides or glycans (more than 10) Homopolysaccharides Heteropolysaccharides

Classification of Monosaccharides

A. Number of carbons in chainTrioses (3C) tetroses (4C) pentoses (5C) hexoses (6C) heptoses (7C)

B. Aldose or Ketose Aldoses (e.g., glucose) have an aldehyde group at one end

Ketoses (e.g., fructose) have a keto group, usually at C2

C

C

CH2OH

OH)n(H

O

H

Aldose

C

C

CH2OH

OHH

O

H

Aldotriosen = 1

C

CH2OH

OHH

C O

H

C OHH

Aldotetrosen = 2

C

CH2OH

OHH

C O

H

C OHH

C OHH

Aldopentose n = 3

C O

H

C OHH

C OHH

CH OH

C

CH2OH

OHH

Aldohexose n = 4

Aldose sugarsAldose sugars

C

C

CH2OH

OH)n(H

O

CH2OH

Ketose

CH2OH

C O

CH2OH

Ketotriose n = 0

CH2OH

C O

C OHH

CH2OH

Ketotetrose n = 1

C OHH

CH2OH

CH2OH

C O

C OHH

Ketopentose n = 2

C OHH

CH2OH

CH2OH

C O

C OHH

OHH

Ketohexose n = 3

Ketose sugarsKetose sugars

Sugars Exhibit Various Forms of Isomerism

Sugars Exhibit Various Forms of Isomerism

Aldose and Ketose isomers

L and D Isomers

Most of the monosaccharides occurring in mammals are D sugars, and the enzymes responsible for their metabolism are specific for this configuration.

1.L-arabinose 2.L-idoronic acid

D Form:

L form:

EnantiomersEnantiomers

Epimers

Two sugars that differ only in the configurationaround one carbon atom are called epimers;

Optical isomerismOptical isomerism

Asymmetric compounds rotate plane polarized light

In general, a molecule with n chiral centers can have 2n stereoisomers

Of the 16 possible aldohexoses, eight are D forms and eight are L

Most of the hexoses of living organisms are D isomers.

POLARIMETRYPOLARIMETRY

Measurement of optical activity in chiral or asymmetric molecules using plane polarized light

Measurement uses an instrument called a polarimeter (Lippich type)

Rotation is either (+) dextrorotatory or (-) levorotatory

polarimetrypolarimetry

Magnitude of rotation depends upon:

1. The nature of the compound

2. The length of the tube (cell or sample container) usually

expressed in decimeters (dm)

3. The wavelength of the light source employed; usually

either sodium line at 589.3 nm or mercury vapor lamp at

546.1 nm

4. Temperature of sample

5. Concentration of analyte in grams per 100 ml

[]DT

l x c

observed x 100 =

D = Na+ lineT = temperature oCobs : observed rotation in degree (specify solvent)l = length of tube in decimeterc = concentration in grams/100ml[] = specific rotation

Polarimetry

Specific rotation of various Specific rotation of various carbohydrates at 20carbohydrates at 20ooCC

D-glucose +52.7D-fructose -92.4D-galactose +80.2L-arabinose +104.5D-mannose +14.2D-arabinose -105.0D-xylose +18.8Lactose +55.4Sucrose +66.5Maltose+ +130.4Invert sugar -19.8Dextrin +195

In chemistry, a racemic mixture, or racemate, is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule.

Racemic mixtureRacemic mixture

A racemate is optically inactive

A racemic mixture is denoted by the prefix (±)- or dl- (for sugars the prefix DL- may be used), indicating an equal (1:1) mixture of dextro and levo isomers

Tartaric acidTartaric acid

• It occurs naturally in many plants, particularly grapes, bananas

• Add to foods to give a sour taste• Used as an antioxidant

levotartaric acid

(D-(−)-tartaric acid)

dextrotartaric acid(L-(+)-

tartaric acid)

mesotartaric acid

Structural representation of sugarsStructural representation of sugars

Fisher projection: straight chain representation

Haworth projection: simple ring in perspective

Conformational representation: chair and boat configurations

Rules for drawing Haworth projectionsRules for drawing Haworth projections

draw either a six or 5-membered ring including oxygen as one atom

most aldohexoses are six-membered

Aldotetroses, Aldopentoses, ketohexoses are five-membered

O O

Pyran Furan

Rules for drawing Haworth projectionsRules for drawing Haworth projections

Next number the ring clockwise starting next to the oxygen

If the substituent is to the right in the Fisher projection, it will be drawn down in the Haworth projection (Down-Right Rule)

O O

1

23

4

5

1

23

4

Rules for drawing Haworth projectionsRules for drawing Haworth projections

For D-sugars the highest numbered carbon (furthest from the carbonyl) is drawn up. For L-sugars, it is drawn down

For D-sugars, the OH group at the anomeric position is drawn down for α and up for β. For L-sugars α is up and β is down

Formation of the two cyclic forms of D-glucose

Conformations: interconvertible without the breakage of covalent bonds, configurations :interconvertible only by breaking a covalent bond—for example, in the case of α and β configurations,

Anomers: Isomeric forms of monosaccharides that differ only in the configuration about the

hemiacetal or hemiketal carbon atom are called

Mutarotation:interconvert of The and anomes of D-glucose in aqueous solution

one-third two-thirds

<1%

Condensation reactions: acetal and ketal formation

D-ribose and other five-carbonsaccharides can form eitherfuranose or pyranose structures

Chair and boat conformations of a pyranose sugar

2 possible chair conformationsof -D-glucose

Envelope Conformations of β - D-ribose

Envelope Conformations

Oxidation reactionsOxidation reactions

Aldoses may be oxidized to 3 types of acids

◦Aldonic acids: aldehyde group is converted to a carboxyl group ( glucose – gluconic acid)

◦Uronic acids: aldehyde is left intact and primary alcohol at the other end is oxidized to COOH Glucose --- glucuronic acid Galactose --- galacturonic acid

◦Saccharic acids: (glycaric acids) – oxidation at both ends of monosaccharide) Glucose ---- saccharic acid Galactose --- mucic acid Mannose --- mannaric acid

Solutions of cupric ion (known as Fehling's solution) provide a simple test for sugars such as glucose. Sugars that react are called reducing sugars; those that do not are called nonreducing sugars

ReductionReduction

either done catalytically (hydrogen and a catalyst) or enzymatically

the resultant product is a polyol or sugar alcohol (alditol)

glucose form sorbitol (glucitol)mannose forms mannitolfructose forms a mixture of sorbitolglyceraldehyde gives glycerol

Sructures of some sugar alcohols

used as a sugar substitute in foods, especially for diabetics. In cosmetics it is commonly used in aftershave lotions, mild soaps and baby shampoos. Sorbitol is used as a humectant and skin conditioning agent

Special monosaccharides: deoxy sugarsSpecial monosaccharides: deoxy sugars

These are monosaccharides which lack one or more hydroxyl groups on the molecule

one quite ubiquitous deoxy sugar is 2’-deoxy ribose which is the sugar found in DNA

6-deoxy-L-mannose (L-rhamnose) is used as a fermentative reagent in bacteriology

examples of deoxysugars

Several sugar esters importantin metabolism

Special monosaccharides: amino sugarsConstituents of mucopolysaccharides

The anomeric forms ofmethyl-D-glucoside

PropertiesProperties

Differences in structuresDifferences in structures of sugars are responsible for of sugars are responsible for variations in propertiesvariations in properties

Physical Crystalline form; solubility; rotatory power

Chemical Reactions (oxidations, reductions, condensations)

Physiological Nutritive value (human, bacterial); sweetness; absorption

OligosaccharidesOligosaccharides

Most common are the disaccharides

Sucrose, lactose, maltose, terehalose

Maltose : 2 molecules of D-glucose

Lactose : glucose + galactose

Sucrose : glucose + fructose

Terehalose : 2 molecules of D-glucose

SucroseSucrose

α-D-glucopyranoside + β-D-fructofuranoside

commercially obtained from sugar cane or sugar beet

hydrolysis yield glucose and fructose (invert sugar) (sucrose: +66.5o ; glucose +52.5o; fructose –92o)

used pharmaceutically to make syrups

Sugar cane

Sugar beet

Sources of sucrose

Non reducing sugarNon reducing sugar

Structure of sucroseStructure of sucrose

LactoseLactose

β-D-galactose (β 1,4) α-D-glucose

used in infant formulations, medium for penicillin production and as a diluent in pharmaceuticals

Reducing sugar

MaltoseMaltose

2-glucose molecules joined via α(1,4) linkage

known as malt sugar

produced by the partial hydrolysis of starch (either salivary amylase or pancreatic amylase)

used as a nutrient (malt extract; Hordeum vulgare); as a sweetener and as a fermentative reagent

reducing sugar

Structure of maltose

Glc(α1 4)Glc

Trehalose

Non reducing sugar

LactuloseLactulose

Galactose-β-(1,4)-fructose

A semi-synthetic disaccharide (not naturally occurring)

Not absorbed in the GI tract

Used either as a laxative

Metabolized in distal ileum and colon by bacteria to lactic acid, formic acid and acetic acid (remove ammonia)

OligosaccharidesOligosaccharides

Trisaccharide: raffinose (glucose, galactose and fructose)

Tetrasaccharide: stachyose (2 galactoses, glucose and fructose)

Pentasaccharide: verbascose (3 galactoses, glucose and fructose)

Raffinose can be hydrolyzed to D-galactose and sucrose by the enzyme α-galactosidase (α-GAL), an enzyme not found in the human digestive tract.

α-GAL also hydrolyzes other α-galactosides such as stachyose, verbascose, and galactinol, if present. The enzyme does not cleave β-linked galactose, as in lactose.

raffinose

stachyose (2 galactoses, glucose and fructose)

verbascose (3 galactoses, glucose and fructose)

Polysaccharides or glycansPolysaccharides or glycans

homoglycans (starch, cellulose, glycogen, inulin)

heteroglycans (mucopolysaccharides)

characteristics: polymers (MW from 200,000) White and amorphous products (glassy) not sweet not reducing; do not give the typical aldose or ketose

reactions) form colloidal solutions or suspensions

Homoglycans

StarchStarch

most common storage polysaccharide in plants

composed of 10 – 30% a-amylose and 70-90% amylopectin depending on the source

the chains are of varying length, having molecular weights from several thousands to half a million

Amylose and amylopectin are the 2 forms of starch. Amylopectinis a highly branched structure, with branches occurring every 12to 30 residues

Amylose and amylopectin, the polysaccharides of starch

amylopectin

Strands of amylopectin form double helicalstructures with each other or with amylose strands

Salivary amylase : Salivary amylase : αα (1-4) endoglycosidase (1-4) endoglycosidase

GGG

G

G

GG

G 1-4 linkG

G

GG 1-6 link

GG

G

GGG G G G

GG

G

G G

G

maltose

G

GG

isomaltose

amylase

maltotriose

G

G

G

G

Limit dextrins

DextrinsDextrins

produced by the partial hydrolysis of starch along with maltose and glucose

used as mucilages (glues)

also used in infant formulas (prevent the curdling of milk in baby’s stomach)

CelluloseCellulose

Polymer of β-D-glucose attached β) linkages

Yields glucose upon complete hydrolysis

Partial hydrolysis yields cellobiose

Most abundant of all carbohydrates Cotton flax: 97-99% cellulose Wood: ~ 50% cellulose

The structure of cellulose(linear, unbranched homopolysaccharide)

Structure of cellulose

GlycogenGlycogenalso known as animal starch

stored in muscle and liver

present in cells as granules (high MW)

contains both a(1,4) links and a(1,6) branches at every 8 to 12 glucose unit

complete hydrolysis yields glucose

hydrolyzed by both a and b-amylases and by glycogen phosphorylase

InulinInulin

β-(1,2) linked fructofuranoses

linear only; no branching

lower molecular weight than starch

hydrolysis yields fructose

sources include onions, garlic, dandelions and jerusalem artichokes

used as diagnostic agent for the evaluation of glomerular filtration rate (renal function test)

Jerusalem artichokes

ChitinChitin

Chitin is the second most abundant carbohydrate polymer

Present in the cell wall of fungi and in the exoskeletons of crustaceans, insects and spiders

Chitin is used commercially in coatings (extends the shelf life of fruits and meats)

Heteropolysacharides

Glycosaminoglycans Glycosaminoglycans (Mucopolysacharides)(Mucopolysacharides)

they are the polysaccharide chains of proteoglycansthey are linked to the protein core via a serine or

threonine (O-linked)the chains are linear (unbranched)the glycosaminoglycan chains are long (over 100

monosaccharides)they are composed of repeating disaccharides

Glycosaminoglycans

Involved in a variety of extracellular functions; chondroitinis found in tendons, cartilage and other connective tissues

Glycosaminoglycans

A characteristic of glycosaminoglycans is the presenceof acidic functionalities (carboxylate and/or sulfates)

Glycosaminoglycans

Proteoglycans are glycosaminoglycan-containing macromolecules of the cell surface and extracellular matrix

Proteoglycan structure

Some proteoglycans can form proteoglycan aggregates

Proteoglycan aggregate of the extracellular matrix

Aggrecan interacts strongly with collagen in the extracellular

matrix of cartilage, contributingto the development and tensile

strength of this connective tissue

Proteoglycans are a family of glycoproteins whose carbohydrate moieties are predominantly glycosaminoglycans

structures are quite diverse as are sizes examples: versican, serglycin, decorin, syndecan

Functions: - modulate cell growth processes - provide flexibility and resiliency to cartilage

Hyaluronate:material used to cement the cells into a tissue

Interactions between cells and the extracellular matrix

Cross-linked meshwork that gives the whole

extracellular matrix strengthand resilience

Bacterial cell wallBacterial cell wall

provide strength and rigidity for the organism

consists of a polypeptide-polysaccharide known as petidoglycan or murein

determines the Gram staining characteristic of the bacteria

Structure of peptidoglycan

Structure of peptidoglycan

Cell wall of Gram-positive bacteria

Gram-negative bacteria

Cross-section of the cellwall of a gram-negativeorganism such as E.coli

Lipopolysaccharide (LPS) coats theouter membrane of Gram-negativebacteria.

the lipid portion of the LPS is embedded in the outer membrane and is linked to a complex polysaccharide

Lipopolysaccharide

Glycoproteins (Mucoprotins)Glycoproteins (Mucoprotins)

Usually done as a post-translational process

Proteins can contain either O-linked oligosaccharides or N-linked oligosaccharides

Serine or threonine O-linked saccharides

Aspargine N-linked glycoproteins

Roles of oligosaccharides in recognition and adhesion

at the cell surface

Complex structure (branching, stereoisomerism)

•Hexasaccharid: 1.05*1012, hexapeptide: 4096, hexanucleotide: 6.4*107

Clone, Expresion, PCR-amplification

Sequencing

synthesis

Lectins are glycoproteins that recognize and bind to specific oligosaccharides.

Recognition/binding of CHO moieties of glycoproteins, glycolipids & proteoglycans by animal lectins is a factor in:

cell-cell recognition adhesion of cells to the extracellular matrix recognition of disease-causing microorganisms initiation and control of inflammation.

Lectins

Glycome:

Glycomics:

•to describe the complete rang of oligosaccharide sequences that can be found in a cell type, organ or organism

•study of glycome by glycoarray

Glycoarray

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