CARBOHYDRATES

CARBOHYDRATES - INTRO

Carbon, hydrogen , Oxygen

( CH2O)n

Polyhydroxy aldehydes/ ketones or compounds which produce them on hydrolysis.

Fns: 1. Dietary source of energy 2. Structure and function of cell membrane 3. Storage form of energy 4. Raw material for industries

CLASSIFICATION

MONOSACCHARIDES

Structure

Optical activity, Epimers, Enantiomers, Diastereomers, Anomers

Reactions of Monosaccharides

Derivatives of Monosaccharides

STRUCTURE OF MONOSACCHARIDES

Simple sugars

Cannot be hydrolysed further

Exhibit Stereoisomerism - Same structural formula but different spatial configuration.

No of stereoisomers possible for a given structural formula - 2^n ( n -No of asymmetric carbon atoms )What are asymmetric carbon atoms? Ans: Those which have 4 different groups attached to them.

1CX3333333333366666nh2 r5555555555555555555555555rrrrrrrrr,,,,,,,,,,,,,,,,,,,,,,,,,,,6

Symmetric and asymmetric carbons

HOW TO DETERMINE IF IT IS D or L FORM?

STEP 1: Determine the terminal primary alcohol carbon

STEP 2: look at the carbon adjacent to the terminal primary alcohol See if -OH group is located on right or left. OH on left → L form OH on right → D form

D forms - naturally occurring forms

Human enzymes can metabolise only D forms

HOW DID DEXTROSE GET ITS NAME?

OPTICAL ACTIVITY OF SUGARS

+ Or - forms + Dextrorotatory and - Levorotatory

Plane polarized light - passed through a sugar solution - will be reflexted either to right or left

Racemic mixture - Equimolar mixture of + and - forms - No net rotation of light

Polarimeter

D- Aldoses

OH group on right Aldehyde group

Killiani - Fischer Synthesis : From Glyceraldehyde ( 3 C D- aldose) → Increasing the size of the structure by 1 C at a time.

D - KETOSES

7 carbon - Sedoheptulose

EPIMERS

When 2 monosaccharides differ from each other in their configuration around a single specific carbon ( other than the anomeric ) → Epimers

Eg: Glucose & Galactose

Epimerisation - interconversion of One epimer to another

Catalysed by epimerases

ENANTIOMERS & DIASTEREOMERS

Stereoisomers that are mirror images of each other → Enantiomers

Not mirror images of each other → Diastereomers

We shall read the structure of Glucose in detail.

Aldehyde/ ketone + Alcohol → Hemiacetal/ Hemiketal

Similarly, the aldehyde group of glucose can react with the alcohol group to form hemiacetal.

ANOMERS / MUTAROTATION

Differ around the anomeric carbon atom → Anomers

Haworth projection Alpha - OH downBeta - OH up

Fischer projectionAlpha - OH right Beta - OH left

Optical rotation of alpha and beta D glucoseEquilibrium - + 52.7 degrees

Mutarotation - Change in specific optical rotation - Interconversion of alpha and beta forms of D glucose to an equilibrium mixture.

REACTIONS OF MONOSACCHARIDES

Tautomerisation / Enolisation Reducing property Oxidation

Reduction Dehydration

Glycoside formnEster formnOsazone formn

TAUTOMERISATION / ENOLISATION

Shift of Hydrogen from one Carbon to another.

Sugar + Alkaline solutions → Enediols ( highly reactive) reducing agents

What is Oxidation?

“ OIL RIG “

Oxdn Is Loss of electrons

Redn is gain of electrons

What is Reduction?

REDUCING PROPERTY OF MONOSACCHARIDES

Free aldehyde/ keto group of anomeric carbon → Reducing agent

Benedict’s / Barfoed’s / Fehling’s test

Alkaline medium → Enediols → Reduction ( remove Oxygen/ add hydrogen/ add electrons)

OXIDATION

Oxidation can occur to the terminal aldehyde/ ketone/alcohol / both.

REDUCTION

GLucose + Reducing agent → Alcohol

DEHYDRATION

Monosaccharides = Conc. H2SO4 → Furfurals

Furfurals + Phenolic compounds → Coloured products ( MOLISCH TEST)

Hexoses → Hydroxymethyl furfural Pentoses → Furfural

OSAZONE FORMATION

Reducing sugars when boiled with Phenylhydrazine in acetic acid

Yield “OSAZONES”

Involves only the 1st 2 carbon atoms

Glucose , Fructose, Mannose ( Needle shaped)

Maltose ( Sunflower)

Lactose ( Powder puff / Hedgehog )

ESTER FORMATION

GLYCOSIDE FORMATION

-OH group of anomeric carbon + Alcohol / Phenol ( -OH group of another carbohydrate or non- carbohydrate) → Glycoside

Non Carbohydrate moiety → Aglycone

Non reducing

MonoS → held together by glycosidic Bonds → Di, Oligo, Poly Saccharides

HOW SHOULD WE NAME THE GLYCOSIDIC BOND?

Find the carbon position - 1 to 6. ( 1→ 4)

Status of anomeric carbon ( alpha or beta depends on position of OH group on anomeric carbon - OH above - beta , OH below alpha)

WHY ARE GLYCOSIDES IMPORTANT?

Glucovanillin - Vanilla flavour

Cardiac glycosides → Digoxin

Streptomycin → Antibiotic

Ouabain → Inhibits Na-K+ ATPase.

DERIVATIVES OF MONOSACCHARIDES

Sugar acids ( Gluconic and Glucuronic acid) → Oxidation

Sugar Alcohol ( Sorbitol, Mannitol) -- Reduction

Alditol ( Xylitol, Ribitol) → Reduction of monosaccharides → Polyhydroxy alcohol

Amino Sugars → Amino instead of OH groups ( D- Glucosamine and D- galactosamine, NANA )

Deoxysugars = One Oxygen less ( DNA )

DISACCHARIDES

DISACCHARIDES

2 monosaccharides with glycosidic bonds

Sweet, crystalline , water soluble

Reducing and non reducing ( Availability of free aldehyde/ keto groups)

Reducing → Maltose, LactoseNon reducing → Sucrose , trehalose

MALTOSE

2 alpha D glucose units Alpha ( 1→ 4 ) Glycosidic linkageSunflower shaped osazonesMaltase hydrolyses maltose to 2 alpha D glucose units

SUCROSE

Cane sugarα D glucose + β -D- Fructose = α - D Glucosyl (1→ 2) β -D- Fructose

Non reducing sugar

No osazones

Hydrolysed by Sucrase → Glucose + Fructose

Sweetening agent

LACTOSE ( MILK SUGAR)

Β- D galactosyl ( 1→ 4 ) β -D Glucose

Reducing sugar

Forms osazone( Powder puff/ Hedge hog )

Hydrolysed by Lactase → Glucose+ galactose

INVERSION OF SUCROSE

Sucrose - Dextrorotatory ( + 66.5degrees)

Sucrase hydrolysis → Glucose + Fructose ( Both Dextro)

But becomes levorotatory . HOW?

Sucrose → α - D Glucopyranose ( +52.5) +β - D Fructofuranose → β -D Fructo Pyranose ( -92)

Net = -28.2 degrees ( levorotatory)

POLYSACCHARIDES

Multiple monosaccharides linked by glycosidic linkages

Fns: 1. Structure of tissues 2. Store energy

Linear or branched

Homopolysaccharides / Heteropolysaccharides

HOMOPOLYSACCHARIDES

Same type of monosaccharides

Eg: Starch , Inulin, Dextrin, Cellulose, Glycogen, Chitin

HETEROPOLYSACCHARIDES

Different types of sugars/ derivatives

Aminosugars + Uronic acid → Glycosaminoglycans ( GAG)

Sulfate + Carboxyl groups → Acidic ( Acid mucopolysaccharides )

MPS + Proteins → Mucoproteins / Proteoglycans

HOMOPOLYSACCHARIDES - STARCH

D- Glucose with α (1→ 4) linkages And branches with α (1->6 ) Linkages

FNS: 1. Storage form of energy in plants2. Dietary source of energy from Carbohydrates

TYPES AMYLOSE: Water solubleUnbranchedD- Glucose units With α (1→ 4) glycosidic linkages

AMYLOPECTIN: Water insolubleBranchedD-Glucose units with α (1→ 4) glycosidic linkages and branching with α (1→ 6) glycosidic linkages ( Branches every 30 glucose units)

AMYLASE - Acts on 1->4 linkages → Dextrin→ Maltose +Glucose

DEXTRINS

Breakdown prducts of starch

Amylase/ Dilute acids

Starch → Soluble starch → Amylodextrin → Erythrodextrin → Achrodextrin → Maltose + Glucose

Coloured by iodine

INULIN

Fructose polymer ( Fructosan)

Found in garlic, onions, dahlia bulbs

Soluble in water

Not utilised by body

Used to assess GFR

GLYCOGEN

Storage form of energy in animals

Liver, muscle, brain

Similar to amylopectin ( branching every 10 glucose units)

D- glucose with α (1→ 4) glycosidic linkages and α (1→ 6) branching points

CELLULOSE

Plant cell wall

β -D Glucose with β( 1-->4 ) Glycosidic linkages

Mammals cannot digest beta forms ( No beta amylases)

Herbivores - gut bacteria - produce beta amylases

Cellulose ---------------------------> Cellobiose --------------------> β -D Glucose

FIBRE - reduces abs of glucose, cholesterol, increases bulk of feces

CHITIN

N - Acetyl - D Glucosamine

β( 1-->4 ) Glycosidic linkages

Exoskeleton of invertebrates ( Insects)

HETEROPOLYSACCHARIDES

Different types of sugars/ derivatives

Mucopolysaccharides, Acid MPS, Proteoglycans

FNS:

1. Tissue structure2. Ground substance

MPS - HYALURONIC ACID

D- Glucuronic acid + N- Acetyl D- Glucosamine linked by β( 1-->3) linkages and interconnected by β( 1-->4 ) linkages

HYALURONIDASE - breaks β( 1-->4 ) Testes, Seminal fluid, snake venom, bacteria

FNS: 1. Synovial fluid2. Vitreous humor3. Gel around ovum

CHONDROITIN SULFATE

D- Glucuronate + N- Acetyl D- Galactosamine 4- SO4 With β( 1-->3) linkages and interconnected by β( 1-->4 ) linkages

FNS: Found in cartilage, skin, tendons, bone, Heart valve & Cornea

HEPARAN SULFATE

L- Iduronate -2 Sulfate + N- Sulpho- D Glucosamine - 6 SO4

FNS:

1. Anticoagulant2. Blood, liver, lung, kidneys, spleen3. Helps release of Lipoprotein lipase - clears the turbidity of lipemic plasma

DERMATAN SULFATE

L - Iduronic acid + N- Acetyl Galactosamine 4 - So4

FNS:

1. Skin2. Blood vessel valves3. Heart valves4. Maintains the shape of tissues

KERATAN SULFATE

D- Galactosamine + N- Acetyl Glucosamine 6 - SO4

FNS:

1. Cartilge 2. Cornea3. Connective tissues4. Keeps cornea transparent

Hyaluronic Acid - GlcUA + GlcNAc

Chondroitin SO4 - GlcUA + GalNAc (4 SO4)

Dermatan SO4 - IdoA + GalNAc ( 4 SO4)

Heparan SO4 - IdoA + N- Sulpho D- Glucosamine 6 SO4

Keratan So4 - GlcNAc 6 SO4 + D- Galactosamine ( Only MPS without Uronic acid)

High C D - Hep Key

Hyaluronic acid, Chondroitin, Dermatan, Heparan, Keratin

D- Glucuronic acid + N acetyl D Glucosamine

D- Glucuronic acid + N acetyl D Galactosamine 4 - Sulfate

L - Iduronic acid + N acetyl D Galactosamine 4 - Sulfate

L - Iduronic acid + N- sulfo D- Glucosamine 6 SO4

N- acetyl D- Glucosamine 6 SO4 + D Galactosamine

GLYCOPROTEINS/ PROTEOGLYCANS

Carbohydrate + Polypeptide chain

CHO < 10% → Glycoprotein > 10% → mucoprotein

Seen in cell membranes and tissues

FNS: Cell membrane, Enzymes, Hormones, transport proteins, receptors.

Eg: Collagen, protease, Ig, Erythropoietin, fibrinogen, blood group substances

Antarctic fish - Antifreeze