Carbohydrates III; Lipids I

1. Carbohydrates III;Lipids I Andy HowardIntroductory Biochemistry, Fall 201021 September 2010 As delivered by Nick Menhart Biochem: Carbo III, Lipids I

2. Sugar Complexes and Lipids • Sugars form complexes with proteins and lipids • Lipids are critical as energy storage molecules and as components of membranes Biochem: Carbo III, Lipids I

3. Glycoconjugates Proteoglycans Peptidoglycans Glycoproteins Lipids Classes of lipids Fatty acids Triacylglycerols Lipids, continued Glycero-phospholipids Plasmalogens Sphingolipids Isoprenoids Steroids Other lipids Plans for Today Biochem: Carbo III, Lipids I

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: Carbo III, Lipids I

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: Carbo III, Lipids I

6. 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 Biochem: Carbo III, Lipids I

7. 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 Biochem: Carbo III, Lipids I

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. 7.30 shows multidimensionality of these walls Biochem: Carbo III, Lipids I

9. 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 Biochem: Carbo III, Lipids I

10. 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 Biochem: Carbo III, Lipids I

11. Gram-negative membranes and periplasmic space Figure courtesy Kenyon College microbiology Wiki Biochem: Carbo III, Lipids I

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: Carbo III, Lipids I

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: Carbo III, Lipids I

14. O-linked and N-linked oligosaccharides • Characteristic sugar moieties and attachment chemistries Biochem: Carbo III, Lipids I

15. O-linked oligosaccharides(fig. fig 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 Biochem: Carbo III, Lipids I

16. 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. Biochem: Carbo III, Lipids I

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: Carbo III, Lipids I

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: Carbo III, Lipids I

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: Carbo III, Lipids I

20. Periodic table of lipids Biochem: Carbo III, Lipids I

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: Carbo III, Lipids I

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: Carbo III, Lipids I

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: Carbo III, Lipids I

24. Bacterial lipids Mostly C12-C18  1 unsaturation Plant lipids High concentration of unsaturated f.a.s Includes longer chains Animal lipds 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: Carbo III, Lipids I

25. Triglyceride composition by source • Courtesy Charles Ophardt, Elmhurst College Biochem: Carbo III, Lipids I

26. Nomenclature for fatty acids • IUPAC names: hexadecanoic acid, etc. • Trivial names from sources (Table 8.1) • 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: Carbo III, Lipids I

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

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: Carbo III, Lipids I

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: Carbo III, Lipids I

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: Carbo III, Lipids I

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: Carbo III, Lipids I

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: Carbo III, Lipids I

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: Carbo III, Lipids I

34. Phospholipids aren’t interchangeable! • Phosphatidylcholine and phosphatidylethanolamine are the major components of eukaryotic membranes • Phosphatidylserine and P-inositol tend to be on the inner leaflet only, and are more prevalent in brain tissue than other tissues • Good reference: http://lipidlibrary.aocs.org/ Biochem: Carbo III, Lipids I

35. 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: Carbo III, Lipids I

36. 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: Carbo III, Lipids I

37. 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: Carbo III, Lipids I

38. 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: Carbo III, Lipids I

39. Plasmalogens • Ether phospholipids have an ether link to C1 instead of an ester linking • Plasmalogens are ether phospholipids with C1 linked via cis-vinyl ether linkage. • They constitute the other major category of phospholipids besides esterified glycerophospholipids • Ordinary fatty acyl esterification at C2…platelet activating factor has R2 = CH3 • Usually PE or PC at C3 position Biochem: Carbo III, Lipids I

40. Specific plasmalogens Biochem: Carbo III, Lipids I

41. 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: Carbo III, Lipids I

42. Sphingolipids • Second-most abundant membrane lipids in eukaryotes • Absent in most bacteria • Backbone is sphingosine:unbranched C18 alcohol • More hydrophobic than phospholipids Biochem: Carbo III, Lipids I

43. Varieties of sphingolipids SphingomyelinImage on steve.gb.com • Ceramides • sphingosine at glycerol C3 • Fatty acid linked via amideat glycerol C2 • Sphingomyelins • C2 and C3 as in ceramides • C1 has phosphocholine Biochem: Carbo III, Lipids I

44. Cerebrosides • Ceramides with one saccharide unit attached by -glycosidic linkage at C1 of glycerol • Galactocerebrosides common in nervous tissue Biochem: Carbo III, Lipids I

45. Gangliosides • Anionic derivs of cerebrosides (NeuNAc) • Provide surface markers for cell recognition and cell-cell communication Biochem: Carbo III, Lipids I

46. Isoprenoids • Huge percentage of non-fatty-acid-based lipids are built up from isoprene units • Biosynthesis in 5 or 15 carbon building blocks reflects this • Steroids, vitamins, terpenes • Involved in membrane function, signaling, feedback mechanisms, structural roles Biochem: Carbo III, Lipids I

47. Isoprene units: how they’re employed in real molecules • Can be linked head-to-tail • … or tail-to-tail (fig. 8.16, G&G) Biochem: Carbo III, Lipids I

48. Steroids • Molecules built up from ~30-carbon four-ring isoprenoid starting structure • Generally highly hydrophobic (1-3 polar groups in a large hydrocarbon); but can be derivatized into emulsifying forms • Cholesterol is basis for many of the others, both conceptually and synthetically Cholesterol:Yes, you need to memorize this structure! Biochem: Carbo III, Lipids I

49. Other lipids Image courtesy cyberlipid.org • Waxes • nonpolar esters of long-chain fatty acids and long-chain monohydroxylic alcohols, e.g H3C(CH2)nCOO(CH2)mCH3 • Waterproof, high-melting-point lipids • Eicosanoids • oxygenated derivatives of C20 polyunsaturated fatty acids • Involved in signaling, response to stressors • Non-membrane isoprenoids:vitamins, hormones, terpenes Image Courtesy Oregon State Hort. & Crop Sci. Biochem: Carbo III, Lipids I

50. Example of a wax • Oleoyl alcohol esterified to stearate (G&G, fig. 8.15) Biochem: Carbo III, Lipids I