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Lecture Notes for Chapter 8 Lipids and Membranes

Essential Biochemistry Third Edition Charlotte W. Pratt | Kathleen Cornely. Lecture Notes for Chapter 8 Lipids and Membranes. KEY CONCEPTS: Section 8-1. Lipids are predominantly hydrophobic molecules that can be esterified but cannot form polymers.

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Lecture Notes for Chapter 8 Lipids and Membranes

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  1. Essential Biochemistry Third Edition Charlotte W. Pratt | Kathleen Cornely Lecture Notes for Chapter 8 Lipids and Membranes

  2. KEY CONCEPTS: Section 8-1 • Lipids are predominantly hydrophobic molecules that can be esterified but cannot form polymers. • Glycerophospholipids and sphingolipids are amphipathic molecules. • Cholesterol and other lipids that do not form bilayers have a variety of other functions

  3. There are several classifications of lipids. • Fatty Acids • Triacylglycerols • Glycerophospholipids • Sphingolipids • Isoprenoids • Cholesterol Lipids (Fats) – Biological molecules that are soluble in nonpolar solvents and poorly soluble in water

  4. Fatty acids are long-chain hydrocarbons. • Amphiphiles • Polar head group: carboxylic acids • Nonpolar tail: hydrocarbon chain • Fatty acids can be saturated with hydrogen, unsaturated, or polyunsaturated.

  5. Fatty acids can be saturated with hydrogens.

  6. Fatty acids can be unsaturated or polyunsaturated. Notice that double bonds are usually in the cis conformation.

  7. Some Common Fatty Acids

  8. Fatty acids are usually found as part of triacylglycerols. R1, R2 and R3 are fatty acid chains

  9. Glycerophospholipids are similar to triacylglycerols. • R1 and R2 are fatty acid chains • X = functional group • Phospholipids are abundant in biological membranes

  10. There are three common head groups on glycerophospholipids. Notice similarities

  11. Phospholipases cleave phospholipids at specific sites.

  12. Sphingolipids • Instead of using glycerol as a backbone,sphingolipids use sphingosine as a backbone.

  13. Sphingomyelin is found in the myelin sheath around nerves. Head group couldalso be a phosphoethanolamine group -O3P-CH2CH2NH3+

  14. Some sphingolipids have monosaccharides as head groups. • A cerebroside is a sphingolipid with a monosaccharide head group.

  15. Some sphingolipids have oligosaccharides as head groups. • A ganglioside is a sphingolipid with an oligosaccharide head group.

  16. Some lipids are derivatives of isoprene.

  17. Cholesterol is an isoprenoid. • Cholesterol is found in biological membranes. • Metabolic precursor of steroid hormones • Estrogen and testosterone • Has amphiphilic character

  18. Ubiquinone is an isoprenoid derivative. • Ubiquinone functions in electron transport.

  19. Fat-soluble vitamins A, D, E and Kare isoprenoid derivatives. • Retinol plays a role in light reception in the eye. • Derives from β-carotene (commonly found in carrots)

  20. Fat-soluble vitamins A, D, E and Kare isoprenoid derivatives. • Sunlight is required for formation of vitamin D molecules. • Ca2+ absorption requires vitamin D.

  21. Fat-soluble vitamins A, D, E and Kare isoprenoid derivatives. • Acts as an antioxidant • Binds to biological membranes

  22. Fat-soluble vitamins A, D, E and Kare isoprenoid derivatives. • Plays a role in blood coagulation

  23. KEY CONCEPTS: Section 8-2 • Bilayer fluidity depends on the length and saturation of its lipids and on the presence of cholesterol. • Lipid asymmetry is maintained by the slow rate of diffusion between leaflets.

  24. Characteristics of the Lipid Bilayer • Fluid • No clearly defined geometry • Head groups move up, down • Hydrocarbon tails wave • Asymmetric • Different lipids are found in each “leaflet” A lipid bilayer

  25. Lipids can form different kinds of bilayers.

  26. The melting point of an acyl chain decreases as the degree of unsaturation increases. Double bonds kink the acyl chain.

  27. Diffusion in membranes differs according to direction.

  28. KEY CONCEPTS: Section 8-3 • Integral membrane proteins completely span the bilayer by forming one or more alpha helices or a beta barrel. • Covalently attached lipids anchor some proteins in the bilayer.

  29. Proteins associate with membranes in different ways. Some lipids anchor proteins in the membrane.

  30. Membrane proteins can span the bilayer. Beta Barrel 8 strands minimum Bacteriorhodopsin20 amino acids/helix

  31. Lipids can be covalently linked to proteins in a variety of ways. Myristoylation Palmitoylation Prenylation

  32. KEY CONCEPTS: Section 8-4 • A membrane’s structure can be described as proteins diffusing laterally within a lipid bilayer.

  33. The Fluid Mosaic Model Membrane proteins float in a sea of lipids and do not transverse the bilayer.

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