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Sugars III; Lipids I

This lecture covers the importance of polysaccharides and lipids in providing energy storage and serving structural roles. It discusses various types of polysaccharides, including amylopectin and glycogen, as well as structural polysaccharides like cellulose and chitin. The lecture also explores glycoconjugates, such as proteoglycans and peptidoglycans, and the role of lipids in energy storage and membrane composition.

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Sugars III; Lipids I

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  1. Sugars III; Lipids I Andy HowardIntroductory Biochemistry, Fall 2014 1 October 2014 Polysaccharides and Lipids

  2. Carbohydrates and Lipids • Polysaccharides provide energy and serve structural roles; protein-sugar complexes have a wide variety of functions • Lipids are critical as energy storage molecules and as components of membranes Polysaccharides and Lipids

  3. Polysaccharides Storage Structural Glycoconjugates Proteoglycans Peptidoglycans Glycoproteins Lipids Periodic table Fatty acid properties Plans for Today Polysaccharides and Lipids

  4. Amylopectin • Mostly a-14 linkages; 4% a-16 • Each sidechain has 15-25 glucose moieties • a-16 linkages broken down by debranching enzymes • 300-6000 total glucose units per amylopectin molecule • One reducing end, many nonreducing ends Polysaccharides and Lipids

  5. Glycogen • Principal storage form of glucose in human liver; some in muscle • Branched (a-14 + a few a-16) • More branches (~10%) • Larger than starch: 50000 glucose • One reducing end,many nonreducing ends • Broken down to G-1-P units • Built up fromG-6-P  G-1-P  UDP-Glucose units Polysaccharides and Lipids

  6. Glycogen structure Polysaccharides and Lipids

  7. Structural polysaccharides I • Insoluble compounds designed to provide strength and rigidity • Cellulose: glucose b-14 linkages • Rigid, flat structure: each glucose is upside down relative to its nearest neighbors (fig.7.27) • 300-15000 glucose units • Found in plant cell walls • Resistant to most glucosidases • Cellulases found in termites,ruminant gut bacteria • Chitin: GlcNAc b-14 linkages:exoskeletons, cell walls (fig. 7.26) Polysaccharides and Lipids

  8. Structural polysaccharides II • Alginates: poly(-D-mannuronate),poly(-L-guluronate), linked 14 • Cellulose-like structure when free • Complexed to metal ions:3-fold helix (“egg-carton”) Sketch courtesy B. Nystrøm, U. Oslo Polysaccharides and Lipids

  9. Structural polysaccharides III • Agarose: alternating D-gal, 3,6-anhydro-L-gal, with 6-methyl-D-gal side chains • Forms gels that hold huge amounts of H2O • Can be processed to use in the lab for gel exclusion chromatography Polysaccharides and Lipids

  10. Sugar Complexes and Lipids • Sugars form complexes with proteins and lipids • Lipids are critical as energy storage molecules and as components of membranes Polysaccharides and Lipids

  11. Glycoconjugates • Poly or oligosaccharidescovalently linkedto proteins or peptides • Generally heteroglycans • Categories: • Proteoglycans (protein+glycosaminoglycans) • Peptidoglycans (peptide+polysaccharide) • Glycoproteins (protein+oligosaccharide) Image courtesy Benzon Symposia Polysaccharides and Lipids

  12. Glycoconjuguates(covalent sugar+peptide) Flowchart summary PeptideorProtein? Peptide Protein Type ofsugar unit Type ofsugar unit Glycos-aminoglycan Oligo-saccharide Poly-saccharide Proteoglycan Glycoprotein Peptidoglycan Polysaccharides and Lipids

  13. Proteoglycans: Glycosaminoglycans • Unbranched heteroglycans of repeating disaccharides • One component isGalN, GlcN, GalNAc, or GlcNAc • Other component: an alduronic acid • —OH or —NH2 often sulfated • Found in cartilage, joint fluid Polysaccharides and Lipids

  14. Proteoglycans in cartilage • Highly hydrated, voluminous • Mesh structure (fig.7.36 or this fig. from Mathews & Van Holde) • Aggrecan is major proteoglycan • Typical of proteoglycans in that it’s extracellular Polysaccharides and Lipids

  15. Peptidoglycans(G&G fig. 7.29) • Polysaccharides linked to small proteins • Featured in bacterial cell walls:alternating GlcNAc + MurNAclinked with -(14) linkages • Lysozyme hydrolyzes these polysaccharides • Peptide is species-specific:often contains D-amino acids Polysaccharides and Lipids

  16. Peptidoglycans in bacteria • Gram-negative: thin peptidoglycan layer separates two phospholipid bilayer membranes • Gram-positive: only one bilayer, with thicker peptidoglycan cell wall outside it • Gram stain binds to thick wall, not thin layer • Fig. 7.30 shows multidimensionality of these walls Polysaccharides and Lipids

  17. Peptide component(G&G fig. 7.29) • Sugars are crosslinked with entities containing(L-ala)-(isoglutamate)-(L-Lys)-(D-ala) • Gram-neg: L-Lys crosslinks via D-ala • Gram-pos: L-lys crosslinks via pentaglycine followed by D-ala Polysaccharides and Lipids

  18. Gram-negative bacteria:the periplasmic space(G&G fig. 7.30b, 7.31) • Periplasmic space: space inside cell membrane but inside just-described peptidoglycan layer (note error in fig. legend!) • Peptidoglycan is attached to outer membrane via 57-residue hydrophobic proteins • Outer membrane has a set of lipopolysaccharides attached to it; these sway outward from the membrane Polysaccharides and Lipids

  19. Gram-negative membranes and periplasmic space Figure courtesy Kenyon College microbiology Wiki Polysaccharides and Lipids

  20. Glycoproteins • 1-30 carbohydrate moieties per protein • Proteins can be enzymes, hormones, structural proteins, transport proteins • Microheterogeneity:same protein, different sugar combinations • Eight sugars common in eukaryotes • PTM glycosylation much more common in eukaryotes than prokaryotes Polysaccharides and Lipids

  21. Diversity in glycoproteins • Variety of sugar monomers •  or  glycosidic linkages • Linkages always at C-1 on one sugar but can be C-2,3,4,6 on the other one • Up to 4 branches • But:not all the specific glycosyltransferases you would need to get all this diversity exist in any one organism Polysaccharides and Lipids

  22. O-linked and N-linked oligosaccharides • Characteristic sugar moieties and attachment chemistries Polysaccharides and Lipids

  23. O-linked oligosaccharides(figs. 7.32a, 7.33 in G&G) • GalNAc to ser or thr;often with Gal or Sialic acid on GalNAc • 5-hydroxylysines on collagen are joined to D-Gal • Some proteoglycans joined viaGal-Gal-Xyl-ser • Single GlcNAc on ser or thr Polysaccharides and Lipids

  24. N-linked oligosaccharides (fig. 7.32b,c in G&G) • Generally linked to Asn • Types: • High-mannose • Complex(Sialic acid, …) • Hybrid(Gal, GalNAc, Man) Diagram courtesy Oregon State U. Polysaccharides and Lipids

  25. iClicker question 1 • Suppose you isolate a polysaccharide with 5000 glucose units, and 4% of the linkages are 1,6 crosslinks. This is: • (a) amylose • (b) amylopectin • (c) glycogen • (d) chitin • (e) none of the above. Polysaccharides and Lipids

  26. iClicker question 2 • Suppose you isolate an enzyme that breaks down -1,4-glycosidic linkages between GlcNAc units. This would act upon: • (a) glycogen • (b) cellulose • (c) chitin • (d) all of the above • (e) none of the above. Polysaccharides and Lipids

  27. Lipids • Hydrophobic biomolecules;most have at least one hydrophilic moiety as well • Attend to “periodic table of lipids”(next slide) • Functions • Membrane components • Energy-storage molecules • Structural roles • Hormonal and signaling roles Polysaccharides and Lipids

  28. Periodic table of lipids Polysaccharides and Lipids

  29. Fatty acids • Unbranched hydrocarbons with carboxylate moieties at one end • Usually (but not always) even # of C’s • Zero or more unsaturations: generally cis • Unsaturations rarely conjugated (why?) • Resting concentrations low because they could disrupt membranes saturated unsaturated Polysaccharides and Lipids

  30. Trans fatty acids • Not completely absent in biology • But enzymatic mechanisms for breakdown of cis fatty acids are much more fully developed • Trans fatty acids in foods derived from (cis-trans) isomerization that occurs during hydrogenation, which is performed to solidify plant-based triglycerides Polysaccharides and Lipids

  31. Fatty acids:melting points and structures • Longer chain  higher MPbecause longer ones align readily • More unsaturations  lower MP • Saturated fatty acids are entirely flexible;tend to be extended around other lipids • Unsaturations introduce inflexibilities and kinks Polysaccharides and Lipids

  32. Bacterial lipids Mostly C12-C18  1 unsaturation Plant lipids High concentration of unsaturated f.a.s Includes longer chains Animal lipids Somewhat higher concentrations of saturated f.a.’s Unsaturations four carbons from methyl group (omega f.a.) common in fish oils Sources for fatty acids Polysaccharides and Lipids

  33. Triglyceride composition by source • Courtesy Charles Ophardt, Elmhurst College Polysaccharides and Lipids

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