CARBOHYDRATESCARBOHYDRATESCARBOHYDRATESCARBOHYDRATES

Carbohydrate Basics

• Primary role: provide the body with energy

• Ultimate Targets: brain and nervous system

• Considered an ideal fuel as compared to other sources of calories

– Less expensive than protein.– Multiple health benefits– High-fat diets are associated with chronic

disease

General Carbohydrate Info• Constitute ¾ of biological world• the term carbohydrate is derived from

the french: hydrate de carbone• compounds composed of C, H, and O• (CH2O)n when n = 5 then C5H10O5

• Made of carbon and water Cn(H2O)n

All carbohydrates are composed of single sugars, alone or in various

combinations

Functions• sources of energy• intermediates in the biosynthesis of

other basic biochemical entities (fats and proteins)

• associated with other entities such as glycosides, vitamins and antibiotics)

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

• participate in biological transport, cell-cell recognition, activation of growth factors, modulation of the immune system

Definition

C

C

C

C

C

CH2OH

OHH

HHO

OHH

OHH

H O

glucose Fructose

Classification of carbohydrates

• Monosaccharides (monoses or glycoses)• Trioses, tetroses, pentoses,

hexosesDisaccharides:• Oligosaccharides

• up to 3 or 10 • Most important are the disaccharides

• Polysaccharides or glycans• Homopolysaccharides• Heteropolysaccharides• Complex carbohydrates

Monosaccharides

• also known as simple sugars• classified by 1. the number of

carbons and 2. whether aldoses or ketoses

• most (99%) are straight chain compounds

• D-glyceraldehyde is the simplest of the aldoses (aldotriose)

• all other sugars have the ending ose (glucose, galactose, ribose, lactose, etc…)

Aldose CHO Ketose C=O

3 carbon atoms

Trioses: glyceraldehyde dihydroxyacetone

4 carbon atoms

Tetroses: erythrose erythrulose

5 carbon atoms

Pentoses arabinose, lyxose, ribose and

xylose

ribulose and xylulose

6 carbon atoms

Hexoses , galactose, glucose .mannose

allose, altrose, gulose, idose, and talose

fructose, psicose, sorbose and

tagatose

7 carbon atoms

Heptoses sedoheptulose

8 carbon atoms

Octoses octolose, 2-keto-3-deoxy-manno-octonate

Octulose

9 carbon atoms

Nonoses: sialose

Isomers

• Isomers – Organic molecules with the same molecular formula but differ in structure or arrangement of atoms.

Chiral Carbons

(+)Glucose (-) Fructose

Fischer Projections

Glyceraldehyde

H O

C C

CH2OH

H OH

H O

C C

CH2OH

HO H

Chiral Carbons

D (+)Glucose D (-) Fructose

Fisher Stereoisomers

CHO

H

OH

H

H

CH2OH

HO

HO

H

HO

CHO

H

HO

H

H

CH2OH

OH

OH

H

OH

L-glucose D-glucose

1

2

3

4

5

6

The (D)-Aldose FamilyThe (D)-Aldotrioses

C

C

CH2OH

HO H

H O

C

C

CH2OH

H OH

H O

One stereocenter two enantiomers

(L)-(-)-glyceraldehyde (D)-(+)-glyceraldehyde

Stereochemical configuration•D = OH above CH2OH on the right

•Configuration of natural aldoses•L-aldoses generally unimportant•No correlation of +/- and D/L

C

C

CH2OH

H OH

H O

epimers

.

                                                                                                                                                                                                                                                                           

Reactions of monosaccharides

• Carbonyl reactions:• Osazone formation• Cyanohydrin reaction• Reduction• Oxidation• Action of base• Action of acid• Ring chain tautomerism

• Alcohol reactions• Glycoside formation• Ether formation• Ester formation

Formation of osazones

• once used for the identification of sugars

• consists of reacting the monosaccharide with phenylhydrazine

• اوزازون + هیدرازین فنیل منوساکارید

• seldom used for identification; we now use HPLC or mass spectrometry

Osazone Formation

1.

                                                                                                                                         

2.

                                                                                                                            

The osazone reaction

Oxidation(or “What does it mean to be a

reducing sugar”)

• Aldehydes can be oxidized to corresponding carboxylic acids

R

H O

R

OH O[O]

Cu(II) Cu(I) Use as a TEST

CHO COOH COOH

(CHOH)n (CHOH)n (CHOH)n

CH2OH 1 CH2OH 2 COOH

Monosacharid Aldonic acid Aldaric acid

glucose gluconic acid glucosacharic acid

3

CHO

(CHOH)n

COOH

Uronic acid

Glucoronic acid

BrOH HNO3

Pt/O2

Oxidation 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

.

                                                                                                                                                                                                                                                                           

Reduction

• 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 mannitol• fructose forms a mixture of mannitol

and sorbitol• glyceraldehyde gives glycerol

Reduction• Carbonyl groups can be reduced to alcohols

(catalytic hydrogenation)

• Sweet but slowly absorbed• Glucose is reduced to sorbitol (glucitol)• Xylose can be reduced to xylitol• Once reduced – less reactive; not absorbed

R

H O[H]

H

R

H OH

Reduction of Monosaccharides

• Reduction of the carbonyl group of a monosaccharide (in open-chain form) produces a sugar alcohol, or alditol

• D-Glucose is reduced to D-glucitol (also called D-sorbitol) using hydrogenation (H2 and a metal catalyst)

Oxidation of Monosaccharides• Recall from Ch.15 that Benedict’s reagent (CuSO4) can oxidize

aldehydes with adjacent hydroxyl groups• The blue Cu2+ ions in the Benedict’s reagent are reduced to form

a brick-red precipitate, Cu2O• Normally, ketones are not oxidized, however ketones with an

adjacent hydroxyl group can rearrange to the aldehyde during reaction with Benedict’s reagent

• So, both aldoses and ketoses, in open chain form, can be oxidized by Benedict’s reagent to form carboxylic acids

• Sugars that can be thus oxidized are called reducing sugars

C

C

C

C

C

CH2OH

HO

OHH

HO H

OHH

OHH

C

C

C

C

C

CH2OH

OHO

OHH

HO H

OHH

OHH

+ Cu2+

D-Glucose D-Gluconic acid

+ Cu2O(s)

Cyanohydrin formation

• reaction of an aldose with HCN• used to increase the chain length of

monosaccharides• results in a cyanohydrin which is then

hydrolyzed to an acid and reduced to the aldehyde

• known as the Fischer-Kiliani synthesis• can prepare all monosaccharides from

D-glyceraldehyde

Reduction of Monosaccharides

• Reduction of the carbonyl group of a monosaccharide (in open-chain form) produces a sugar alcohol, or alditol

• D-Glucose is reduced to D-glucitol (also called D-sorbitol) using hydrogenation (H2 and a metal catalyst)

Oxidation of Monosaccharides• Recall from Ch.15 that Benedict’s reagent (CuSO4) can

oxidize aldehydes with adjacent hydroxyl groups• The blue Cu2+ ions in the Benedict’s reagent are reduced to

form a brick-red precipitate, Cu2O• Normally, ketones are not oxidized, however ketones with an

adjacent hydroxyl group can rearrange to the aldehyde during reaction with Benedict’s reagent

• So, both aldoses and ketoses, in open chain form, can be oxidized by Benedict’s reagent to form carboxylic acids

• Sugars that can be thus oxidized are called reducing sugars

C

C

C

C

C

CH2OH

HO

OHH

HO H

OHH

OHH

C

C

C

C

C

CH2OH

OHO

OHH

HO H

OHH

OHH

+ Cu2+

D-Glucose D-Gluconic acid

+ Cu2O(s)

Monosaccharides can form ring structures

Condensation reactions: acetal and ketal formation

Cyclic Forms of Monosaccharides                As noted above, the preferred structural form of many monosaccharides may bethat of a cyclic hemiacetal. Five and six-membered rings are favored over other ring sizes because of their low angle and eclipsing strain. Cyclic structures of this kind are termed furanose (five-membered) or pyranose (six-membered), reflecting the ring size relationship to the common heterocyclic compounds furan and pyran shown on the right. Ribose, an important aldopentose, commonly adopts a furanose structure, as shown in the following illustration. By convention for the D-family, the five-membered furanose ring is drawn in an edgewise projection with the ring oxygen positioned away from the viewer. The anomeric carbon atom (colored red here) is placed on the right. The upper bond to this carbon is defined as beta, the lower bond then is alpha. Click on the following diagram to see a Chime model of β-D-ribofuranose.                                                                                                                                                                                                                                                                                                                                                                      

               

D-Glucose(an aldose)

    Cyclation of Glucose

α-D-Glucose β-D-Glucose

+H2O

• Glucose usually makes hemiacetal cyclic structures with six atom rings, although five membered rings can also be formed when the six membered rings are precluded. Such six membered rings are named by the term "pyranose." The ring forms look like this, keeping in mind that alpha and beta anomers are also involved here:

:

                                                                                                                             

.

                                                                                                                                                                                                                                                                                                                                                                         

amino sugars 1- آمین های قنددار

Constituents of mucopolysaccharides

استر قندها

examples of deoxysugars

استر قندها

glucose-1-phosphate

H O

OH

H

OHH

OH

CH 2OH

H

OPO32

H

Several sugar esters importantin metabolism

CHO

OHH

OHH

OHH

CH2OH

1

4

2

3

5

D-ribose

CHO

HH

OHH

OHH

CH2OH

1

4

2

3

5

2-Deoxy-D-ribose

H

OH

H

HOH2C

OH OH

H HO

H

OH

H

HOH2C

OH H

H HO

CHO

H

OHH

OHH

HHO

CH2OH

1

4

2

3

5

6

HO

L-Galactose

OH

HO

OH

HHO

HOH

H

H

CH2OH

6

2

3

4

5

1

CHO

H

OHH

OHH

HHO

CH3

1

4

2

3

5

6

HO

6-Deoxy-L-Galactose(fucose)

OH

HO

OH

H

HO

HOH

H

H

CH3

6

2

3

4

5

1

+ = پیرویک اسید آمین مانوز سیالیک اسیداسید = + آمین دگلوکز استیل مورامیک اسید

الکتیک

Examples of glycosides

Disaccharides• A disaccharide is formed when a hydroxyl

group on one monosaccharide reacts with the anomeric carbon of another monosaccharide to form a glycosidic bond

• Each disaccharide has a specific glycosidic linkage (depending on which hydroxyl reacts with which anomer)

• The three most common disaccharides are maltose, lactose and sucrose

• When hydrolyzed using acid or an enzyme, the following monosaccharides are produced:

Maltose + H 2O D-Glucose + D-Glucose

Acid

orenzyme

Lactose + H 2O D-Glucose + D-Galactose

Acid

orenzyme

Sucrose + H 2O D-Glucose + D-Fructose

Acid

orenzyme

Maltose• Maltose (malt sugar or corn sugar) consists of

two glucose molecules linked by an -1,4-glycosidic bond

• It comes from partial hydrolysis of starch by the enzyme amylase, which is in saliva and also in grains (like barley)

• Maltose can be fermented by yeast to produce ethanol• Maltose is also used in cereals, candies and malted milk• Because one of the glucose molecules is a hemiacetal, it can undergo mutorotation, and so maltose is a reducing sugar

Lactose• Lactose (milk sugar) consists of one glucose

molecule and one galactose molecule linked by a -1,4 glycosidic bond

• It comes from milk products (about 4-5% of cow’s milk)

• Because the glucose is a hemiacetal, it can undergo mutorotation, and so lactose is a reducing sugar

Hydrolysis of Lactose• Some people don’t produce enough lactase,

the enzyme that hydrolyzes lactose, and so can’t digest lactose

• Many adults become lactose intolerant, and develop abdominal cramps, nausea and diarrhea

• Lactase can be added to milk products (or taken as a supplement) to combat this problem

Cellobiose

Sucrose• Sucrose (table sugar) consists of one glucose

molecule and one fructose molecule linked by an ,-1,2-glycosidic bond

• Sucrose is the most abundant disaccharide and is commercially produced from sugar cane and sugar beets

• Because the glycosidic bond in sucrose involves both anomeric carbons, neither monosaccharide can undergo mutorotation, and so sucrose is not a reducing sugar

CH2OH

OHCH2OH

OH

OHO

O

OH OH

OH

OH

CH2OH

alpha-D-Glucose

beta-D-Fructose

1

2

O

OH

OH

OH

CH2OH

1

CH2OH

CH2OH

OH

OHO

2

O

+alpha,beta-1,2-glycosidic bond

Sucrose

Hydrolysis of Sucrose• Sucrose is hydrolyzed by the enzyme

sucrase, which is secreted in the small intestine

• The glucose and fructose can then be absorbed into the bloodstream (disaccharides are too large to be absorbed)

Trehalose

• Two glucose molecules with an a 1,1 linkage

• Non reducing, mild sweetness, non-hygroscopic

• Protection against dehydration

                            

Oligosaccharides

• Trisaccharide: raffinose (glucose, galactose and fructose)

• Tetrasaccharide: stachyose (2 galactoses, glucose and fructose)

• Pentasaccharide: verbascose (3 galactoses, glucose and fructose)

• Hexasaccharide: ajugose (4 galactoses, glucose and fructose)

Honey also contains glucose and fructose along withsome volatile oils

Polysaccharides or glycans

• homoglycans (starch, cellulose, glycogen, inulin)

• heteroglycans (gums, 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

Starch

• most common storage polysaccharide in plants

• composed of 10 – 30% 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

H O

OH

H

OHH

OH

CH 2OH

HO H

H

OHH

OH

CH 2OH

H

O

HH H O

OH

OHH

OH

CH 2

HH H O

H

OHH

OH

CH 2OH

H

OH

HH O

OH

OHH

OH

CH 2OH

H

O

H

O

1 4

6

H O

H

OHH

OH

CH 2OH

HH H O

H

OHH

OH

CH 2OH

HH

O1

OH

3

4

5

2

glycogen

                                                                                                                                                                                   

                                                                        

suspensions of amylosein water adopt a helical conformation

iodine (I2) can insert inthe middle of the amylosehelix to give a blue colorthat is characteristic anddiagnostic for starch

Cellulose

• Polymer of -D-glucose attached by (1,4) linkages

• Yields glucose upon complete hydrolysis• Partial hydrolysis yields cellobiose• Most abundant of all carbohydrates

• Cotton flax: 97-99% cellulose• Wood: ~ 50% cellulose

• Gives no color with iodine• Held together with lignin in woody plant

tissues

Linear structures of cellulose and chitin (2 most abundant polysaccharides)

Products obtained from cellulose

• Microcrystalline cellulose : used as binder-disintegrant in tablets

• Methylcellulose: suspending agent and bulk laxative

• Oxidized cellulose: hemostat• Sodium carboxymethyl cellulose:

laxative• Cellulose acetate: rayon; photographic

film; plastics• Cellulose acetate phthalate: enteric

coating• Nitrocellulose: explosives; collodion

(pyroxylin)

Glycogen

• also known as animal starch• stored in muscle and liver• present in cells as granules (high MW)• contains both (1,4) links and (1,6)

branches at every 8 to 12 glucose unit• complete hydrolysis yields glucose• glycogen and iodine gives a red-violet

color• hydrolyzed by both and -amylases

and by glycogen phosphorylase

Inulin

-(1,2) linked fructofuranoses• linear only; no branching• lower molecular weight than starch• colors yellow with iodine• 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

Chitin

• 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)

Chitin

• 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)

Dextrans

• products of the reaction of glucose and the enzyme transglucosidase from Leuconostoc mesenteroides

• contains (1,4), (1,6) and (1,3) linkages

• MW: 40,000; 70,000; 75,000• used as plasma extenders (treatment of

shock)• also used as molecular sieves to separate

proteins and other large molecules (gel filtration chromatography)

• components of dental plaques

Dextrins

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

• dextrins are often referred to as either amylodextrins, erythrodextrins or achrodextrins

• used as mucilages (glues)• also used in infant formulas

(prevent the curdling of milk in baby’s stomach)

Polysaccharides

• A polysaccharide is a polymer consisting of hundreds to thousands of monosaccharides joined together by glycosidic linkages

• Three biologically important polysaccharides are starch, glycogen and cellulose

- all three are polymers of D-glucose, but they differ in the type of glycosidic bond and/or the amount of branching

• Starch and glycogen are used for storage of carbohydrates

- starch is found in plants and glycogen in animals

- the polymers take up less room than would the individual glucose molecules, so are more efficient for storage

• Cellulose is a structural material used in formation of cell walls in plants

Plant Starch (Amylose and Amylopectin)• Starch contains a mixture of amylose and amylopectin• Amylose is an unbranched polymer (forms -helix) of D-glucose molecules

linked by -1,4-glycosidic bonds• Amylopectin is like amylose, but has extensive branching, with the branches

using -1,6-glycosidic bonds

Glycogen and Cellulose• Glycogen (animal starch) is like amylopectin,

except it’s even more highly branched- animals store glycogen in the liver (about a one-day supply in humans) and use it to maintain fairly constant blood sugar levels between meals

• Cellulose is an unbranched polymer of D-glucose molecules linked by -1,4-glycosidic bonds- cellulose forms -sheets of parallel strands held together by hydrogen bonding- we don’t have the enzyme to break down cellulose- some animals have microorganisms that do have the enzyme

Iodine Test for Starch

• The presence of starch can easily be identified using iodine (I2)

• Rows of iodine atoms form in the core of the -helix of amylose, forming a dark blue complex

• Because amylopectin, glycogen and cellulose do not form -helices, they do not complex well with iodine, so do not show the blue color (they show a purple or brown color)

• Monosaccharides do not interact with the iodine, so no color is produced

Glycosaminoglycans

• they are the polysaccharide chains of proteoglycans

• they 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

Hyaluronate (hyaluronan) is a glycosaminoglycan with a repeating disaccharide consisting of 2 glucose derivatives, glucuronate (glucuronic acid) & N-acetyl-glucosamine.

The glycosidic linkages are (13) & (14).

H O

H

H

O HH

O H

COO

H

H O

O H H

H

NH COCH 3H

CH 2O H

H

OO

D -g lucuronate

O

1

23

4

5

61

23

4

5

6

N -acetyl-D -g lucosam ine

hyaluronate

Mucoitin Sulfateاستر سولفوریک اسیدهیالورونیک را

موکوایتین سولفات میگویند که در ترشحات مخاطی وجوددارد. ویک الیه نگهبان روی سطح مخاطی مثل روده

ایجاد کرده ومانع آسیب آنزیمها .میشود

Glycosaminoglycans

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

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

هپارین• اسید وایدورونیک سولفات آمین گلوکز

Hyaluronic acid derivatives

• several products are used in the management of osteoarthritis symptoms– Hyalagan and Synvisc

• others are used as ophthalmic surgical adjuncts in cataract extractions, intraocular lens implantation, corneal transplant and retinal attachment surgery (Healon, Amvisc, AMO Vitrax)

Glycosaminoglycans

Bacterial 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 ofpeptidoglycan

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 embeddedin the outer membrane and is linked toa complex polysaccharide