|Lecture Notes: 20 October||
Cellulose: -1,4 linkages, thus resistant to breakdown (including acid hydrolysis) as want for structure (don't want to digest self). Multiple, extended strands come together as fibrils held together with H-bonds (text Figure 7-15a,b), laid down in cell wall in criss-cross pattern, glued together with polyalcohols (lignin).
Remember, the -glycosidic bond is very difficult to break down. Thus cellulose which is linked by -bonds, can essentially only be digested by bacteria because of this bond.
So animals can't digest cellulose! You may ask, What about Cows and things? Well they use bacteria. Cows for instance are basically walking fermentation tanks.
Cool biological examples of cellulose use by animals: Desert Iguana consume feces to maintain culture; Rabbits eat and reprocess first pass feces (soft) to take advantage of fermentation; Multiple stomachs in Ruminants; Ultimate symbiosis in some termites: protozoans in gut have bacteria in gut, and use spirochetes as "cilia" (rowers).
Chitin: Serves similar role to cellulose, but in animals (crustaceans and insects), fungi, and some algae. Homopolymer of N-acetyl-D-glucosamine. Like cellulose , it has -1,4 linkages, and is thus resistant to breakdown. (text Figure 7-17a)
Among the heteropolysaccharides are the glycosaminoglycans (text Figure 7-22a). As an example hyaluronic acid (hyaluronan) , an alternating polysaccharide of D-glucuronic acid and N-acetyl-D-glucosamine can have 50,000 repeats of the dissacharide (MW to 5,000,000) which serves as a lubricant in joints and is a component of the vitreous humor. Again we see -1,4 linkages.
Compare in Table 7-2
Also very important are the glycans (proteoglycans) conjugated to proteins and peptides to give glycoproteins (text Figures 7-24, 7-25, 7-29 )
Recall the lipid definition: The portion of an organism which will partition into a non-polar solvent.
Types of Lipids: (text Figure 10-6)
A summary of common fatty acids is shown in Table 10-1 of the text.
Last modified 21 October 2008