CARBOHYDRATE CHEMISTRY

LOURDES L. BALCUEVA, M.D.

CARBOHYDRATE CHEMISTRY

• Most abundant biomolecule in nature• Widely distributed in plants and animals• Main source of energy in humans;

oxidation of carbohydrates is the central energy-yielding pathway in most non-photo-synthetic cells

Carbohydrate Chemistry

Other functions of CHO: - insoluble carbohydrate polymers serve as protective and structural elements in bacterial cell walls , plants, and connective tissues of animals - lubricate skeletal joints - attached to proteins, act as signals that determine intracellular location of glucoprotein

CARBOHYDRATE CHEMISTRY

• - Carbohydrates are aldehyde or ketone derivative of polyhydric alcohol - General formula: Cn(H2O)n - Ex. Glucose: C6H12O6

- Glucose- most important carbohydrate; most dietary CHOs are absorbed in the circulation as glucose; - Glucose is the major metabolic fuel of mammals and fetuses.

NOMENCLATURE

• 1. Monosaccharides- carbohydrate molecules with only one actual or potential sugar group; - cannot by hydrolyzed into simpler carbohydrates 2.Disaccharides- when 2 monosaccharides are combined together with release of water molecule; hydrolysis produces 2 monosaccharide units

Carbohydrates

• 3. Oligosaccharides- condensation products of 2-10 monosaccharide units• 4. Polysaccharides- condensation products of more than 10 monosaccharides

Monosaccharides

• - colorless, crystalline solids• - soluble in water but not in non-polar solvents - sweet taste - backbone is unbranched C chain; all carbon atoms are linked by single bonds - One C atom is double-bonded to an oxygen atom to form carbonyl grp.

Aldose and ketose

• Aldose- if the carbonyl grp. is at the end of the carbon chain; monosaccharide is an aldehyde Ketose- if the carbonyl grp. is at any other position; monosacharide is a ketone

Monosaccharides

Structure of Glucose

Haworth and Chair Form

Monosacchides

• - monosaccharides with 5 or more carbon atoms in the backbone occur as cyclic structures in solution - carbonyl grp. forms covalent bond with oxygen of a hydroxyl grp along the chain

Stereoisomers

• Stereoisomers-compounds having the same structural formula but differ in spatial

configuration - depends on the number of asymmetric C atom - formula: 2n where n is the number of asymmetric carbon atom - ex. Glucose: 2n is equal to 16

Diastereo-isomers• Monosaccharides with the same molecular• Formula but differ in the configuration about 2

carbon atoms• Ex. Mannose and galactose

• Epimers- when sugars differ from one another only in configuration about one

carbon atom• Ex. Glucose and mannose; glucose and galactose

Enantiomers

D and L isomers

Enantiomers

Optical Activity

• - the ability of a solution to rotate the plane of plane-polarized light towards the right or

towards the left. - to the right or dextrorotatory: ( + ) - to the left or levorotatory: ( - ) -gives rise to 2 structures that are mirror image to each other called enantiomers

Pyranose and Furanose RingStructure

• - results from general reaction between aldehydes and alcohols forming hemiacetals or between ketones and alcohols forming hemiketal - only aldoses with 5 or more carbon atoms can form pyranose rings - OH at C5 reacts with aldehyde grp at C1 - results in asymmetry at C1 resulting in a and B stereoisomers of D-glucose

Pyranose and Furanose Structures

a and B-stereoisomerism

Glucose

Glycosidic bond

• - monosacharides joined covalently by o-glycosidic bond

Glycosidic Bond• Joins together 2 monosaccharides through a reaction

between the anomeric carbon of one unit and a hydroxyl group of another.

• Nomenclature: • - monosaccharide on the left: unit where the anomeric carbon is involved - O precedes the name of the first monosaccharide - a or B configuration of the first unit - furanosyl or pyranosyl - ( no. of C atom of first unit no. of C atom of 2nd unit)

Disaccharides

Disaccharides

Disaccharides

Polysaccharides

Glycogen

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