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Carbohydrates and Lipids

Carbohydrates and Lipids. Andy Howard Biochemistry Lectures, Fall 2010 4 October 2010. Carbohydrates and lipids: two out of three. Carbohydrates are vital as energy sources, and they also serve as building blocks for lipid-carbohydrate and protein-carbohydrate complexes

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Carbohydrates and Lipids

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  1. Carbohydrates and Lipids Andy HowardBiochemistry Lectures, Fall 2010 4 October 2010 Biochem: Carbohydrates&Lipids

  2. Carbohydrates and lipids: two out of three • Carbohydrates are vital as energy sources, and they also serve as building blocks for lipid-carbohydrate and protein-carbohydrate complexes • Lipids are long-term energy sources and play critical roles in membranes, as well as being significant building blocks Biochem: Carbohydrates&Lipids

  3. Glycoconjugates Proteoglycans Peptidoglycans Glycoproteins Lipids Categories Fatty acids Triacylglycerols Phospholipids What we’ll discuss Biochem: Carbohydrates&Lipids

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

  5. 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 Biochem: Carbohydrates&Lipids

  6. Proteoglycans in cartilage • Highly hydrated, voluminous • Mesh structure (fig.8.29 or this fig. from Mathews & Van Holde) • Aggrecan is major proteoglycan • Typical of proteoglycans in that it’s extracellular Biochem: Carbohydrates&Lipids

  7. Peptidoglycans(Horton fig. 8.30) • 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 Biochem: Carbohydrates&Lipids

  8. 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. 8.31(b) suggests multidimensionality of these walls Biochem: Carbohydrates&Lipids

  9. Peptide component(Horton fig. 8.31(a)) • 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 Biochem: Carbohydrates&Lipids

  10. Gram-negative bacteria:the periplasmic space • Horton fig. 8.30, G&G fig. 7.37 • 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 Biochem: Carbohydrates&Lipids

  11. Gram-negative membranes and periplasmic space Figure courtesy Kenyon College microbiology Wiki Biochem: Carbohydrates&Lipids

  12. 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 Biochem: Carbohydrates&Lipids

  13. 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 Biochem: Carbohydrates&Lipids

  14. O-linked and N-linked oligosaccharides • Characteristic sugar moieties and attachment chemistries Biochem: Carbohydrates&Lipids

  15. O-linked oligosaccharides • Horton fig. 8.33a • 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 Biochem: Carbohydrates&Lipids

  16. N-linked oligosaccharides (fig. 8.33b in Horton) • Generally linked to Asn • Types: • High-mannose • Complex(Sialic acid, …) • Hybrid(Gal, GalNAc, Man) Diagram courtesy Oregon State U. Biochem: Carbohydrates&Lipids

  17. iClicker question 1 • Suppose you isolate a polysaccharide with 5000 glucose units, and 3% of the linkages are 1,6 crosslinks. This is: • (a) amylose • (b) amylopectin • (c) glycogen • (d) chitin • (e) none of the above. Biochem: Carbohydrates&Lipids

  18. 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. Biochem: Carbohydrates&Lipids

  19. 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 Biochem: Carbohydrates&Lipids

  20. Periodic table of lipids Compare with Horton fig. 9.1 Biochem: Carbohydrates&Lipids

  21. 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 Biochem: Carbohydrates&Lipids

  22. 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 Biochem: Carbohydrates&Lipids

  23. 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 Biochem: Carbohydrates&Lipids

  24. 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 Biochem: Carbohydrates&Lipids

  25. Triglyceride composition by source • Courtesy Charles Ophardt, Elmhurst College Biochem: Carbohydrates&Lipids

  26. Nomenclature for fatty acids • IUPAC names: hexadecanoic acid, etc. • Trivial names from sources(G&G Table 8.1; Horton table 9.1) • Laurate (dodecanoate) • Myristate (tetradecanoate) • Palmitate (hexadecanoate) • Palmitoleate (cis-9-hexadecenoate) • Oleate (cis-9-octadecenoate) • Linoleate (cis,cis-9,12-octadecadienoate) • Arachidonate(all cis-5,8,11,14-eicosatetraeneoate) Biochem: Carbohydrates&Lipids

  27. Saturated Fatty Acids Contrast withmelting points of Unsaturated C18 FAs: 16ºC, -5ºC -11ºC;C20, 4 double bonds: -50ºC Biochem: Carbohydrates&Lipids

  28. How fatty acids really appear • Almost always esterified or otherwise derivatized • Most common esterification is to glycerol • Note that glycerol is achiral but its derivatives are often chiral • Triacylglycerols; all three OHs on glycerol are esterified to fatty acids • Phospholipids: 3-OH esterified to phosphate or a phosphate derivative glycerol Biochem: Carbohydrates&Lipids

  29. Triacylglycerols • Neutral lipids • R1,2,3 all aliphatic • Mixture of saturated & unsaturated; unsaturatedmore than half • Energy-storage molecules • Yield >2x energy/gram as proteins or carbohydrates, independent of the water-storage issue … • Lipids are stored anhydrously; carbohydrates & proteins aren’t Biochem: Carbohydrates&Lipids

  30. Catabolism of triacylglycerol • Lipases break these molecules down by hydrolyzing the 3-O esters and 1-O esters • Occurs in presence of bile salts(amphipathic derivatives of cholesterol) • These are stored in fat droplets within cells, including specialized cells called adipocytes Biochem: Carbohydrates&Lipids

  31. Glycerophospholipids • Also called phosphoglycerides • Primary lipid constituents of membranes in most organisms • Simplest: phosphatides (3’phosphoesters) • Of greater significance: compounds in which phosphate is esterified both to glycerol and to something else with an —OH group on it Biochem: Carbohydrates&Lipids

  32. Categories of glycerophospholipids • Generally categorized first by the polar “head” group; secondarily by fatty acyl chains • Usually C-1 fatty acid is saturated • C-2 fatty acid is unsaturated • Think about structural consequences! Biochem: Carbohydrates&Lipids

  33. Varieties of head groups • Variation on other phosphoester position • Ethanolamine (R1-4 = H) (—O—(CH2)2—NH3+) • Serine (R4 = COO-)(—O—CH2-CH-(COO-)—NH3+) • Methyl, dimethylethanolamine(—O—(CH2)2—NHm+(CH3)2-m) • Choline (R4=H, R1-3=CH3) (—O—(CH2)2—N(CH3)3+) • Glucose, glycerol . . . Biochem: Carbohydrates&Lipids

  34. Chirality in common lipids • Fatty acyl chains themselves are generally achiral • Glycerol C2 is often chiral (unless C1 and C3 fatty acyl chains are identical) • Phospholipid polar groups are achiral except for phosphatidylserine and a few others Biochem: Carbohydrates&Lipids

  35. iClicker quiz question 3 • What is the most common fatty acid in soybean triglycerides? • (a) Hexadecanoate • (b) Octadecanoate • (c) cis,cis-9,12-octadecadienoate • (d) all cis-5,8,11,14-eicosatetraeneoate • (e) None of the above Biochem: Carbohydrates&Lipids

  36. iClicker quiz, question 4 • Which set of fatty acids would you expect to melt on your breakfast table? • (a) fatty acids derived from soybeans • (b) fatty acids derived from olives • (c) fatty acids derived from beef fat • (d) fatty acids derived from bacteria • (e) either (c) or (d) Biochem: Carbohydrates&Lipids

  37. iClicker quiz question 5 • Suppose we constructed an artificial lipid bilayer of dipalmitoyl phosphatidylcholine (DPPC) and another artificial lipid bilayer of dioleyl phosphatidylcholine (DOPC).Which bilayer would be thicker? • (a) the DPPC bilayer • (b) the DOPC bilayer • (c) neither; they would have the same thickness • (d) DOPC and DPPC will not produce stable bilayers Biochem: Carbohydrates&Lipids

  38. Plasmalogens • Another major class besides phosphatidates • C1 linked via cis-vinyl ether linkage. • n.b. Garrett & Grisham figure 8.10 is one page later than the discussion of it • Similarly, Horton fig.9.9 is one page later than the discussion thereof • Ordinary fatty acyl esterification at C2 • Phosphatidylethanolamine at C3 Biochem: Carbohydrates&Lipids

  39. Specific plasmalogens Biochem: Carbohydrates&Lipids

  40. Roles of phospholipids • Most important is in membranes that surround and actively isolate cells and organelles • Other phospholipids are secreted and are found as extracellular surfactants (detergents) in places where they’re needed, e.g. the surface of the lung Biochem: Carbohydrates&Lipids

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