OIA1003 W6 CARBOHYDRATES STRUCTURE & FUNCTION

Carbohydrate?

Most abundant organic molecules in nature

C + H + O

Empirical formula: (CH2O)n

Providing dietary calories

Storage form of energy in the body

Serving as cell membrane components (intercellular communication)

Structural components of organism - bacterial cell walls, exoskeleton & fibrous cellulose

Classification of Carbohydrate?

Monosaccharides

Cannot hydrolysed into simpler carbohydrates

Classified according to number of C atoms, contain - trioses, tetroses, pentoses, hexoses or heptoses

Consists: 3-6 atoms, carbonyl gp (aldehyde or ketone), several OH gps

Aldoses: mono with aldehyde gp & many OH

Ketoses: mono with ketone gp & many OH

Isomers - same chemical formula but different strucutres

Epimers - differ in configuration around only one specific C atom (except carbonyl C)

Enationmers - special type of isomerism pairs of structures that mirror images of each other

Cyclisation of Monosaccharides - 5 or 6 C sugar spontaneously cyclise -> Furan or Pyran ring

Cyclisation of Glucose - spontaneous & reversible

In closed cyclic form, forms a new OH gp and adds in new stereocenter in the sugar

New Stereocenter = Anomers

Cyclisation -> form new stereocenter at ring closure position (anomers)

Create anomeric C generate a & B configuration of sugar

OH at anomeric C1: a (OH below ring) & B (OH above ring)

Glycosidic Bond - create larger structure

Reaction - easily oxidised (reducing sugar)

Less glucose concentration, more Cu colour (brick red)

Disacchardies - condensation products of 2 monosaccharides, contain a glycosidic bond

Oligosaccharides - carbo chain contain 3-10 monosaccharides

Made of any sugar monomer (E.g., fructooligosaccharides, galactooligosaccharides)

Few are hydrolysed & absorbed, almost all enter colon intact

Polysaccharides - condensation products of >10 monosaccharides

Polymer of D-glucose

Examples:

Starch: A-D-glucose (amylose & amylopectin)

Polysaccharides of glucose units link via glycosidic bonds

Glucose combine to form 2 polymer components (differ in structure & properties) -> starch

Glycogen: a-D-glucose (animal starch)

Storage polysaccharides in animals, highly branched structure than amylopectin

Glucose molecules linked via alpha 1-4 glycosidic bonds

Branching occur at every 8-12 subunit & each new branch contain 8-12 glucose (each branch link to main chain via alpha 1-6 glycosidic bond)

Cellulose: B-D-glucose (plants)

Cheif component of plant cell wall

Insoluble & consists B-D-glucose linked by B-1, 4-bonds to form long straight chain strengthened by cross-linking H bonds

Other Non-starch Polysaccharides

Insulin: Polysaccharides of fructose (alpha fructosan) in tubers & roots of plant

Dextrins: Group of low MW polymeric carbo produced by starch or glycogen hydrolysis

Chitin: Structural polysaccharides in exoskeleton of crustaceans & insects

Pectin: soluble fiber in fruits