Ch8-120220 - CHEM 350 Introduction to Biological Chemistry...

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Unformatted text preview: CHEM 350: Introduction to Biological Chemistry Brian Lee, Ph.D. [email protected] Office: Neckers 146G or 324 Phone: 453-7186 Ho urs: 9:30am to 10:30am or by appointment Website: https:/ / Textbook (required, U.S. edition only) Fundamentals of Biochemistry, 3rd Ed., Voet, Voet & Pratt. Study Guide (recommended) Student Companion to Fundamentals of Biochemistry, 3rd Ed. Help Desk Tuesday 6:30 to 7:30 pm in Neckers 218 Thursday 5:00 to 6:00 pm in Neckers 410 Announcements Undergraduate Research Opportunities Research for credit (such as CHEM 396 or CHEM 496) Student worker ($8.00 per hour) ( Undergraduate Assistantships ( McNair Scholars Program ( REACH Awards Competition ( Summer Research Experiences for Undergraduates (REU) Deadline for SIUC REU Program is March 7th For other REU programs, search the National Science Foundation site: Students must contact the individual sites for information and application materials. NSF does not have application materials and does not select student participants. A contact person and contact information is listed for each site. Assignments Read Chapter 9 Lipids and Biological Membranes Chapter 9 Problems Student Companion site for Voet, Voet & Pratt Second Midterm Exam, Wednesday February 29th Chapters 6 through 9 (All exams are cumulative) No class on Monday, February 27th (no office hours) Help Desk Tuesday 6:30 to 7:30 pm in Neckers 218 Thursday 5:00 to 6:00 pm in Neckers 410 The free anomeric carbon is also a mild reducing agent. Saccharides with a free anomeric carbon that has not formed a glycoside are called reducing sugars. Reactions with Cu2+ solution (Fehling’s solution) or Ag+ (Tollens’ reagent) are used to detect reducing sugars. -D-glucose D-glucose D-gluconate The ano meric carbon is oxidized to a carboxylic acid group. The anomeric carbon is more reactive than other sugar carbons Reactions with alcohols and amines form adducts through glycosidic bonds: note the suffix “-side” Nucleosides are also adducts between sugar and base Reaction with methanol Oligosaccharides Sugars linked by O-glycosidic bonds defined by the carbon atom positions Sucrose is a 1->2 linkage between both anomeric carbons of glucose and fructose, thus sucrose is a non-reducing sugar. Polysaccharides for energy storage: Glycogen - (animals) -1,4 glucose chains with -1,6 branches at every 10 units Starch - (plants) Amylose - -1,4 glucose chains Amylopectin - -1,4 glucose chains with -1,6 branches at every 30 units glycogen The most stable structure for starch and glycogen is a coiled helix stabilized by inter-chain hydrogen bonds with six residues per turn. Amylopectin and Glycogen are both branched with a brush-like structure. Branched structures are more compact than linear forms, allowing more efficient energy storage. The most abundant organic molecule is cellulose, Structural component of plant cell walls, ß1->4 linkages produce straight chains of cellulose; Ideal for constructing fibers and indigestible by mammals. cellulose fibers in algae Chitin (arthropod exoskeletons). N-acetylglucosamine residues in 1->4 linkage. Same as cellulose, except for the C2-N-acetyl group June bug Heteropolysaccharide: Agarose - component of red algae cell walls. Agarose gels - heated agarose solutions form a gel upon cooling. Double helical structures trap water molecules. Ideal for electrophoretic separations of nucleic acid (DNA) molecules. Bacterial cell walls: Peptidoglycan This is the target of lysozyme. Heteropolysaccharide chains cross-linked by short peptides. Glycosaminoglycans - gel-like, in extracellular matrix. Often disaccharide repeats. O- and N-sulfate & N-acetyl. Slimy and mucous-like due to high viscosity and elasticity. Chondroitin 4-sulfate & keratin sulfate cartilage & connective tissue. D-Glucuronate N-Acetyl-Dgalactosamine4-sulfate D-Galactose N-Acetyl-Dglucosamine6-sulfate Glycosaminoglycans - gel-like, in extracellular matrix. Hyaluronate - synovial fluid in joints and vitreous humor in eye D-Glucuronate + Heparin - most negatively charge polyelectrolyte, associated with arterial walls, released during injury, prevents excess clotting. N-Acetyl-D-glucosamine D-Glucuronate-2-sulfate or L-Iduronate-2-sulfate N-SulfoD-glucosamine6-sulfate Proteoglycan structure: Cell surface or extracellular matrix. Glycosaminoglycan chains are joined covalently to a membrane protein or a secreted protein. Proteoglycan aggregates: Supramolecular assemblies of aggrecan core proteins bound to a single molecule of hyaluronate (Example, proteoglycan aggregate of the extracellular matrix). Keratan sulfate and chondroitin sulfate are linked to Ser residues of aggrecan core to form brush-like structures. Glycoproteins - most eukaryotic proteins are covalently associated with a carbohydrate Proteoglycan - linked to glycosaminoglycans, found in cartilege and connective tissue Peptidoglycan - network of covalently linked polysaccharides and polypeptide, encase bacterial cells Other glycoproteins - are found in the cytosol, associated with the cell membrane and in extracellular spaces. Sugars can be N-linked through asparagine or O-linked through serine or threonine residues. Glycoproteins: proteins covalently linked to oligosaccharides. They have specific sites for recognition and high-affinity binding by other proteins “Sequence” of glycosylation is highly specific to species and tissue, which permits specific recognition of cell types. Glycoforms vary the content and sequence of sugars attached to a particular protein. Glycosylation can be branched into brush-like structures that are specifically recognized by cell surface receptors. Table 8-1 Glycosylation begins in the ER and terminal glycosylation takes place in the Golgi complex. Glycosylation directs intracellular transport in vesicles with targeting to the plasma membrane, extra-cellular matrix or internal vesicles such as the lysosome. Lysosome contains digestive enzyme that degrade and recycle cellular components as well as digest extracellular material Glycolipids: lipids with oligosaccharide head groups-gangliosides and lipopolysaccharides Lectins are proteins that bind to specific carbohydrate structures Lectins participate in cell-cell contacts Hemagglutinin from influenza virus binds to sialic acid sugars to gain entry into human cells. Sialic acid recognition ...
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