Carbohydrates

Carbohydrates

Aldehydes or ketone derivatives of polyhydric alcohols.

[C.H2.O]n

Monosaccharides

Basic units of carbohydrates that cannot be hydrolyzed into a simpler form.

Water soluble white crystalline solids that have a sweet taste.

Disaccharide

Carbohydrate which can be hydrolyzed into 2 molecules of the same/different monosaccharide.

C12H22O11 (C12H24O13 - H2O)

1. Maltose: makes up starch

2. Sucrose: most abundant

3. Lactose

4. Cellobiose: found in cellulose

Maltose

D-glucose + D-glucose

Joined head-to-tail through C1 to C4 via a-1,4-glycosidic linkage.

Reducing sugar

Hydrolyzed by maltase

Lactose

D-galactose + D-glucose

Joined by Ɓ-1,4-glycosidic linkage.

Hydrolyzed by dilute mineral acids or lactase.

Cellobiose

D-glucose + D-glucose

Joined Ɓ-1,4-glycosidic bonds.

Reducing sugar

Sucrose

D-glucose + D-fructose

Joined in a-1,2-glycosidic bond (because of this bond cannot exist in the a-/Ɓ- configuration or open chain form. So it doesn’t exhibit mutarotation and exists only in one form in solid state or solution).

Can be hydrolyzed by mineral acids or sucrose.

Non-reducing sugar (potential aldehyde group of glucose and potential keto group of fructose are involved in the 1,2-glycosidic linkage, therefore does not undergo reaction characteristic to aldehydes and ketones)

Oligosaccharides

Carbohydrates which can be hydrolyzed into 3-20 of the same/different monosaccharide.

1. Fructooligosaccharide (FOS)

2. Galactooloigosaccharide (GOS)

Polysaccharide

Carbohydrate which can be hydrolyzed into more than 20 monosaccharide units. (C6H10O5)n

Structural function and storage form of energy. Hydrolyzed by enzymes to yield monosaccharides.

1. Only 1 type of monosaccharide units present. Starch, glycogen, cellulose and chitin

2. 2 or more different monosaccharide units present. Glycoproteins, Glycolipids, Peptidoglycans, Glycosaminoglycans, Proteoglycans.

Starch

1. Amylose: 98%, liner polymer of glucose linked by a-1,4-glycosidic bonds. Non-reducing and reducing ends. Gives blue volour with iodine.

2. Amylopectin: highly branched polymer of glucose (24-30) a-1,6-glycosidic bond. Produce purple to red colour with iodine. Helix form interrupts the colour formation with iodine.

Glycogen

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

Cellulose

Linear homopolysaccharide of D-glucosr linked by Ɓ(1-4) glycosidic bonds. It’s got a structure of parallel chains linked by H2 bonds lying side by side to form a stable fibrous network by intra and inter-chains hydrogen bonds.

Resistant to hydrolysis.

Ruminants, exception (bacteria that resides within) secrete a Ɓ-glucosidase, cellulase. Termites (parasite in digestive tract) that secretes cellulase.

Chitin

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

Also forms extended fibers

Glycoproteins

Oligo/polysaccharide covalently bound with proteins.

Carbohydrate can contain up to 4 branches and are O-linked to serine/threonine or N-linked to asparagine. Units can be joined by either a-or Ɓ-glycosidic linkage

Glycolipids

Oligo/polysaccharide covalently joined to lipids.

These linear polymers lie side by side in the bacterial cell wall and in the human plasma membrane.

Peptidoglycans

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

Alternating Ɓ(1-4) linkages between N-Acetyl-Glucose (GlcNAc) and N-Acetyl-Muramic acid (MurNAc).

These linear polymers lie side by side in the cell wall and cross-linked by short peptides. Which are degraded by lysozome (which hydrolyses the glycosidic bond between monosaccharides and kills bacteria) and is present in tears.

Glycosamino-glycans

Usually located in the extracellular matrix. Acts as a porous pathway for the diffusion of nutrients and oxygen to the individual cells.

Composed of repeating disaccharide units. This is simply called hyaluronic acid (hialuronate) at physiological pH it contains alternating units of D-glucoronic acid and N-Acetyl glucosamine.

Hyaluronidase enzyme secreted by some pathogenic bacteria makes tissue more susceptible to bacterial infection

Isomers

Molecules consisting of the same number and kinds of atoms but differ in their structure or spatial configuration.

1. Structural

2. Stereo (optical)

Structural isomers

Same molecular formula but differ in structural formula

1. Aldose-ketose isomerism: When one aldose sugar and one ketose sugar are same in molecular formula but differ in structural formula

2. Pyranose-furanose isomerism: When a pyranose ring and a furanose ring of carbohydrates are the same molecular formula but differ in structural formula.

   Hemiacetal formation (characteristic reaction between aldehydes and alcohols. The aldehyde group of C1 and hydroxyl group of C5 combine.)

   Hemiketal formation (characteristic reaction between ketone and alcohols. Ketone group at C2 and hydroxyl at C5 of a fructose molecule combine together)

Optical (stereo) isomers

Same structural formula but differ spatial configuration

1. Asymmetric (chiral) center: a carbon atom to which 4 different atoms are attached

2. Enantiomers: When two optical (stereo) isomers are mirror images to each other. D & L.

3. 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. (Diastereomers- neither epimer nor enantiomers)

4. Anomers: When a monosaccharide cyclases an asymmetric carbon is formed resulting in the formation of 2 different structures. a & Ɓ

Optical activity

1. Dextrorotatory (+): When an optically active compound rotates the plane of polarized light on clockwise direction

2. Levorotatory (-): When an optically active compound rotates the plane of polarized light on anticlockwise direction

Specific rotation

Specific angle at which a compound rotates the plane of polarized light

Standard measure degree of the compound which is D or L.

Two enantiomers have equal and opposite specific rotation

Mutarotation

The gradual change of optical rotations of two compounds which continue until equilibrium is established