Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 438

Introductory Biochemistry

Spring 2010

Lecture Notes: 10 March

© R. Paselk 2006
 
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CARBOHYDRATES, cont.

Sucrose, Sucrase (Invertase), and the magic of liquid filled chocolate covered cherries.

POLYSACCHARIDES

Can have both homo- and heteropolysaccharides. We will focus on homopolysaccharides as most central, but will mention some heteropolysaccharides to illustrate their functions. Homopolysaccharides have a single type of residue. Most common polysaccharides contain glucose. Used for energy (food) storage (starches and glycogen) and structure (cellulose).

Starch (energy storage in plants). Two kinds

Glycogen: animal starch. Just like amylopectin, but more highly branched (every 8-12 residues). This allows more free ends for more rapid breakdown-important in animals.

STRUCTURAL POLYSACCHARIDES

Cellulose: beta-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 (Figure 8.25, 8.26) [overhead 10.15, V&V], laid down in cell wall in criss-cross pattern, glued together with polyalcohols (lignin).

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 beta-1,4 linkages, and is thus resistant to breakdown. (Figure 8.27)

Among the heteropolysaccharides are the glycans such as Hyaluronic acid, an alternating polysaccharide of D-glucuronic acid and N-acetyl-D-glucosamine; MW to 5,000,000 (Figure 8.28) which serves as a lubricant in joints and is a component of the vitreous humor. Again we see beta-1,4 linkages.

Also very important are the glycans conjugated to proteins and peptides to give proteoglycans (Figure 8.29).

LIPIDS

Recall the lipid definition: The portion of an organism which will partition into a non-polar solvent.

Types of Lipids: (Figure 9.1) [overhead 11.1, P]

palmitic acid structure

stearic acid structure

oleic acid structure

glycerophospholipoid structure

Lipid Properties: An important consideration for lipids of all sorts is their fluidity. Thus membranes must be fluid enough to allow the diffusion of proteins, transport processes etc. but not so fluid as to weaken the membranes structure. For storage want fat to be fluid enough to flow to fill out body shape at normal operating temperatures. A number of strategies are used by organisms to adjust lipid fluidity:


Pathway Diagrams

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Last modified 10 March 2010