Carbohydrate Structure and Function
structural formula of carbohydrates :
is (CH2O)n
Carbohydrates are classified as aldehyde (-CHO)or
Ketone (-C=O) has a large hydroxyl group (OH) binding. therefore : called compounds polyhydroxyaldehyde or polyhydroxyethylene
Glycoproteins
Proteoglycans
-Long linear chains of glycoaminoglycans (mucopolysaccharides) attached to core protein
-Repeating disaccharide units: uronic acid-hexosamine
-Uronic acid: D-glucuronic acid or L-iduronic acid
-Hexosamine: D-glucosamine or D-galactosamine or derivative (acetylated and sulfate attached)
Negative charge: be heavily hydrated----> cushion or lubricant
Serve as enzymes, lubricants, hormones, antibodies and structural proteins
Involve in cell attachment and recognition sites
Structures contain mannose, L-fucose and N-acetylneuraminic acid (NANA) in addition to glucose, galactose and amino derivatives
N-linked glycosylation: Asparagine
O-linked glycosylation: Serine and Threonine
Glycolipids
Derived from ceramide
Cerebrosides: Glucose, Galactose
Gangliosides: N-acetylneuraminic acids
Carbohydrate functions
Major fuel source: glucose
Storage energy: starch and glycogen
Structural component: cell wall (cellulose, chitin and peptidoglycan) and cell membrane
Metabolic intermediates: glucose-6-phosphate
Components of the nucleotides: ribose and deoxyribose
Play roles in lubrication: glycoaminoglycan and proteoglycan
Cellular intercommunication: glycoprotein/glycolipid
Type of Carbohydrate and Classsification
Monosaccharides
therefore classified according to the number of carbon atoms became a trios(triose , 3C), tetrose (4C), pentone (5C).
Functional groups consists of 2 groups in a molecule
aldose, which has an aldehyde functional group
ketose, which has a functional group as a ketone group
Stereoisomer is formed by having at least one asymmetric carbon atom.
Fischer projection
D isomer: hydroxyl group on the reference carbon is on the right
Chemical and physical properties
1.Mutarotation “ Anomerism of Sugars” : α and β froms equilibrate via the straight-chain aldehyde form ; Mutarotase
2.Epimerization “Epimerism of Aldoses” : Isomerase and Epimerase
3.Enediol Formation : Ketose > Aldose ; in Alkaline solutions.
4.Oxidation : Reducing suger is oxidized with oxidizing reagent or glucose oxidase catalysis
5.Reduction : aldoses and ketoses may be reduced at the carbonyl carbon to polyhydroxy alcohol or polyalcohlo
6.Glycosidation : a sugar reacts with an alcohol to form glycoside
7.Phosphorylation : Kinase + ATP
Oligosaccharide
1.Sucrose
It consists of glucose and fructose connected by alpha glycoside bonds.
2.Lactose
is a monosaccharide mainly found in mammalian milk. The full name of lactose is B-D-galactopyranosyl (1—>4)-D-glucopyzanose.
3.Moaltose
consists of 2 glucose molecules connected by
a 1—> 4 bond.
Polysaccharide
-Polymer of monosaccharide (100- <1,000 molecules) with glycosidic bonds
Linear or branch polymer
1.Homopolysaccharide
-Starch : amylose and amylopectin
- Glycogen
- Cellulose
- Chitin (N-acetyl-D-glucosamine polymer)
- Heteropolysaccharides
- Peptidoglycan (N-acetyl-D-glucosamine +N-acetylmuramic acid)
- Glycoaminoglycan: Hyaluronic acid, chondroitin sulphate,keratan sulphate, dermatan sulphate and heparin
L isomer: hydroxyl group on the reference carbon is on the left
Application of carbohydrates
Sugar substitute
Ex.acesulfame potassium, aspartame, neotame, saccharin, steviol glycosides, sucralose, cyclamate, thaumatin, neohesperidin dihydrochalcone.
These sugars are therefore considered to be low in calories or less energy than sugar.
Fat substitute
The most commonly used carbohydrates are oligosaccharides, polysaccharides, which thicken food.
Drug Delivery
carbohydrate polymers are biomolecules found in the body, they have the potential to be excellent drug delivery vessels due to their inherent biocompatibility and ability to be excreted from the body after the drugs have been delivered.
Used to reduce or replace the use of animal fats in products.