Carbonhydrates and isomers

Carbohydrate

Aldehyde or ketone derivatives of polyhydric (multiple OH groups) alcohols. [C.H2O]n.

1. Monosaccharides

2. Disaccharide

3. Oligosaccharide

4. Polysaccharide

Monosaccharide

Carbohydrates that cannot be hydrolyzed into simpler forms = Basic units.

Water soluble white crystalline solids that have sweet taste.

1. Trioses

2. Tetroses

3. Pentoses

4. Hexoses

5. Heptoses

Disaccharide

C12H22O11 (C12H24O12 - H2O)

Two monosaccharide units linked by glycosidic linkage

Difference between Maltose [a(1,4) glycosidic bond] and cellobiose [B(1,4) glycosidic bond]

1. Maltese = D-glucose + D-glucose a(1-4) glycosidic bonds

2. Sucrose = D-glucose + D-fructose

3. Lactose = D-glucose + D-galactose

4. Cellobiose = D-glucose + D-glucose B(1-4) glycosidic bonds

Oligosaccharide

Carbohydrates that can be hydrolyzed into 3-20 of the same/different monosaccharide units

Fructooligosaccharide (FOS) & Galactooligosaccharides (GOS)

Polysaccharide

Carbohydrates which can be hydrolyzed into more than 20 monosaccharides units

Molecular weight ranges from 1000-150000

(C6H10O5)n

Structural function and storage form of energy

Examples: Starch, glycogen, Cellulose, Chitin, Glycoproteins, Glycolipids, Peptidoglycans, Glycosaminoglycans, Proteo-glycans

Isomer

Molecule that consists of same number and kinds of atoms but differ in their structure or spatial configurations

1. Structural

2. Optical (stereo)

Structural isomer

Compounds that have the same molecular formula but differ in structural formula

1. Aldose ketose isomerism

2. Pyranose-Furanose Ring isomerism

Aldose-Ketose isomerism

When one aldose sugar and one ketose sugar are the same in molecular formula but differ in structural formula

D-Glyceraldehyde/Dihydroxyacetone

D-Glucose/D-fructose

Pyranose-Furanose isomerism

When Pyranose ring and a Furanose ring of carbohydrates are the same in molecular formula but differ in structural formula

D-Glucose (pyranose) & D-Fructose (Furanose)

Haworth projections : open chain forms of aldohexose and ketohexose and soke other sugars react internally to form cyclic hemiacetals and hemiketals

Hemiacetal and Hemiketal formation

Characteristic reaction between aldehydes and alcohols

Characteristic reaction between ketone and alcohol

Pyranose ring formation

Aldehyde group (-CHO) at C1 and hydroxyl (-OH) at C5 of a glucose molecule combined together

Hemiketal formation

Ketone group at C2 and hydroxyl group at C5 of a fructose molecule combined together to synthesize a furanose ring

Optical/stereo isomer

Compounds that have the same structural formula but different spatial configuration

Form due to presence of asymmetric/ chiral center / chiral carbon atom

Asymmetric/ chiral center

Carbon with 4 different atoms/groups of atoms attached to it

Includes all monosaccharide except dihydroxy-acetone

Think D&L

Enantiomers

Two optical (stereo) isomers are mirror images to each other

D&L

Epimers

Isomers that differ as a result of variation in configuration of the H or OH on a single C atom of a hexose molecule

Glucose: Mannose & Galactose (diastereomers)

Anomers

When monosaccharide cyclases, an asymmetric center is formed. Two different structures are formed based on asymmetric carbon

a-D glucose (OH group is below plane of ring)

Ɓ-D glucose (OH group is above plane of ring)

Anomeric carbon

When 2 oxygen atoms are bonded to a single carbon atom in a ring structure compound

Optical isomers/activity

The presence of asymmetric carbon confers the optical activity on the compound. Optical isomers are also mirror images to each other hence their enantiomers, these compounds have similar properties (same boiling points, same melting points, same solubility) but different optical activity. They names Dextrorotatory and Levorotatory

Dextrorotatory

D(+): when an optically active compound rotates the plane of polarized light clockwise

Levorotatory

L(-): when optically active compound rotates the plane of polarized light anticlockwise

Specific rotation

A specific amount of angle rotates by the plane of polarize light for a particular compound

Standard measure degree of the compound which is D(+) and L(-)

Two enantiomers have equal and opposite specific rotation a-D glucose (+112°) and Ɓ-D glucose (+19°). D-bromobutane (+23.1°) and L-bromobutane (-23.1°)

Mutarotation

The gradual change of optical rotation of 2 compounds which continues until equilibrium is reached.

From the values of specific rotation and mutarotation the composition of the a- and Ɓ form of a given compound in a mixture can be calculated. Sometimes compounds can be separated based on physical features

Maltose

D-Glucose+D-Glucose - a(1,4) bonds

Formed by enzyme action (diastase in plants; ptyalin in animals) hydolysis of starch. Hydrolyzed by maltase. The 2 a-D-glucopyranose components are joined head-to-tail through C1 and C4 with a-1-4-glucosidic linkage.

Reducing sugar

Lactose

Hydrolyzed by dilute mineral acid/ lactase. Monosaccharide units (Glucose+Galactose) joined by a Ɓ-1,4-glycodic linkage.

(a form = infant food and penicillin)

Equilibrium mixture of a- and Ɓ- form = +55°

Cellobiose

Stereo isomer of maltose, Glucose+Glucose - B(1,4) bonds. 2 glucose units joined by Ɓ-1,4-glycosidic bond.

Reducing sugar, mutarotation

Sucrose

C1 of a-D-glucose and OH group of C2 of Ɓ-D-fructose linked by a-1,2-glycosidic bond which can be hydrolyzed by mineral acids or sucrase.

Mutarotation: none; 1,2-glycosidic bond cannot exist in a/Ɓ configuration or in the open chain form (exist only as a solid or in solution)

Non-reducing: potential aldehyde group of glucose and potential keto group of fructose are involved in the 1,2-glycosidic linkage in sucrose

Homopolysaccharide

1 type of monosaccharide unit make up polysacharride

1. Storage: starch glycogen

2. Structural: cellulose and chitin

Starch

Made up of Glucose

1. Amylase (98%): linear polymer of 100-1000 glucose units. Non reducing & reducing ends. Blue in iodine

2. Amylopectin (2%): highly branched polymer (24-30 glucose units) Purple/red in iodine. Each branch point has a(1,6) glycosidic linkage. Helix form interrupt the colour formation with iodine

   Potential aldehyde group of glucose and potential keto group of fructose are involved in 1,2 glycosidic linkage i

Glycogen

Highly branched polysacchiride of glucose linked by a(1,4) and a(1,6) linkages (8-12 units). Non reducing.

Cellulose

Linear homopolysaccharide of D-glucose linked by Ɓ(1-4) glycosidic bonds. Consists of 300-15000 units. Structure of parallel chains linked by H2 bonds lying side by side to form stable fibrous network of intra/interchains hydrogen bonds. Insoluble in water.

Ɓ(1,4) glycosidic bonds resistant to hydrolysis. Exceptions: ruminants- bacteria inside rumen secrete cellulase, a Ɓ-glucosidase, that catalyzed the hydrolysis of cellulose. Termites, digestive tract has parasites that secrete cellulase.

Chitin

Linear homopolysaccharide of N-acetyl-D-glucosamine residues linked by Ɓ(1-4) linkages.

Also forms extended fibres

Heteropolysaccharide

2 or more different types of monosaccharides present in polysaccharides

Glycoproteins

Oligo/polysaccharide covalently joined to proteins. Carbohydrate part = 80% of total mass, can contain up to 4 branches and O linked to serine or threonine but N linked to asparagine

Glycolipids

Oligo/short chain polysaccharide convalently joined to lipids. Linear polymers lie side by side in bacterial cell wall and in human plasma (5%)

Peptidoglycans

Polysaccharide linked to small peptide. Rigid component of bacterial cell wall.

Alternating Ɓ(1-4) linkage between N-Acetyl-Glucose (GlcNAc) and N-Acetyl-Muramic acid (MurNAc). Linear polymers lie side by side in cell wall and cross linked by short peptides.

Degraded by lysozyme which hydrolyses glycosidic bond between monosaccharides and kills bacteria (present in tears)

Proteoglycan and glycosaminoglycans

Make up extracellular matrix (interlocking network of heteropolysaccharides and fibrous proteins). Acts as porous pathway for diffusion of nutrients and O2 to individual cell

Glycosaminoglycans: linear polymer composed of repeating disaccharides

Hyaluronic acid: alternating units of D-glucoronic acid and N-acetyl glucosamine. Hyaluronidase make tissue more susceptible to bacterial invasion and infection (similar enzyme in sperm)