Oligosaccharides and Polysaccharides: Structures and Functions PDF

Oligosaccharide  Oligosaccharides Trisaccharide: raffinose (glucose, galactose and fructose) Tetrasaccharide: stachyose (2 galactoses, glucose and fructose) Pentasaccharide: verbascose (3 galactoses, glucose and fructose) Hexasaccharide: ajugose (4 galactoses, glucose an...

Oligosaccharide  Oligosaccharides Trisaccharide: raffinose (glucose, galactose and fructose) Tetrasaccharide: stachyose (2 galactoses, glucose and fructose) Pentasaccharide: verbascose (3 galactoses, glucose and fructose) Hexasaccharide: ajugose (4 galactoses, glucose and fructose) Oligosaccharides that are covalently CH2OH C O attached to proteins H O O CH2 CH or to membrane H NH serine OH H residue lipids may be linear OH O H or branched chains. H HN C CH3 -D-N-acetylglucosamine Polysaccharide  Polysaccharides or glycans Nomenclature: homopolysaccharide (homoglycans) vs. heteropolysaccharide (heteroglycans). homoglycans (starch, cellulose, glycogen, inulin) heteroglycans (gums, mucopolysaccharides). characteristics: polymers (MW from 200,000) White and amorphous products (glassy) not sweet not reducing; do not give the typical aldose or ketose reactions) form colloidal solutions or suspensions  CH2OH 6CH OH CH2OH CH2OH CH2OH 2 O 5 O H O H O H H O H H H H H H H H H H H OH H 1 4 OH H 1 OH H OH H OH H O O O O OH OH 2 3 H OH H OH H OH H OH H OH amylose Polysaccharides: Plants store glucose as amyloseor amylopectin, glucose polymers collectively called starch. Glucose storage in polymeric form minimizes osmotic effects. 1. Amyloseis a glucose polymer with (14) linkages. The end of the polysaccharide with an anomeric C1 not involved in a glycosidic bond is called the reducing end.  CH2OH CH2OH H O H H O H amylopectin H H OH H OH H 1 O OH O H OH H OH CH2OH CH2OH 6 CH2 CH2OH CH2OH H O H H O H H 5 O H H O H H O H H H H H H OH H OH H OH H 1 4 OH H OH H 4 O O O O OH OH 2 3 H OH H OH H OH H OH H OH 2. Amylopectinis a glucose polymer with mainly (14) linkages, but it also has branches formed by (16) linkages. Branches are generally longer than shown above. The branches produce a compact structure & provide multiple chain ends at which enzymatic cleavage can occur.  CH2OH CH2OH H O O glycogen H H H H H OH H OH H 1 O OH O H OH H OH CH2OH CH2OH 6 CH2 CH2OH CH2OH H O H H O H H 5 O H H O H H O H H H H H H OH H OH H OH H 1 4 OH H OH H 4 O O O O OH OH 2 3 H OH H OH H OH H OH H OH 3. Glycogen, the glucose storage polymer in animals, is similar in structure to amylopectin but glycogen has more (16) branches. The highly branched structure permits rapid glucose release from glycogen stores, e.g., in muscle during exercise.  CH2OH 6CH OH CH2OH CH2OH CH2OH 2 O 5 O O H O H O OH H H H H H H H H OH H 1 O 4 OH H 1 O OH H O OH H O OH H OH H H H H 2 H 3 H OH H OH H OH H OH H OH cellulose 4. Cellulose, a major constituent of plant cell walls, consists of long linear chains of glucose with (14) linkages. Every other glucose is flipped over, due to  linkages. This promotes intra-chain and inter-chain H-bonds formation. 5. Dextrans If you change the main linkages between glucose from alpha (1,4) to alpha (1,6), you get a new family of polysaccharides – dextrans. Branches can be (1,2), (1,3) or (1,4). Dextrans formed by bacteria are components of dental plaque. Cross-linked dextrans are used as "Sephadex" gels in column chromatography. These gels are up to 98% water. Because of the -linkages, cellulose has a different overall shape from amylose, forming extended straight chains which hydrogen bond to each other, resulting in a very rigid structure. Cellulose is the most important structural polysaccharide, and is the single most abundant organic compound on earth. It is the material in plant cell walls that provides strength and rigidity; wood is 50% cellulose. Most animals lack the enzymes needed to digest cellulose, but it does provide roughage (dietary fiber) to stimulate contraction of the intestines and help pass food through the digestive system. However, some animals, such as cows, sheep and horses (ruminants), can process cellulose through the use of colonies of bacteria in the digestive system which are capable of breaking cellulose down to glucose; ruminants use a series of stomachs to allow cellulose a longer time to digest. Some other animals such as rabbits reprocess digested food to allow more time for the breakdown of cellulose to occur. Cellulose is also important industrially, from its presence in wood, paper, cotton, cellophane, rayon, linen, nitrocellulose (guncotton), photographic films (cellulose acetate), etc.  Lactose Intolerance more lactose is consumed than can be digested – lactose molecules attract water cause bloating, abdominal discomfort, diarrhea – intestinal bacteria feed on undigested lactose to produce acid and gas