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Lipids

Lipids. Highly diverse structures Unifying property Hydrophobic: little to no affinity to water Contains hydrocarbons, which form nonpolar covalent bonds Do not form polymers Biologically important lipids containing molecules: Fats Phospholipids Steroids. Fats. Structure

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Lipids

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  1. Lipids • Highly diverse structures • Unifying property • Hydrophobic: little to no affinity to water • Contains hydrocarbons, which form nonpolar covalent bonds • Do not form polymers • Biologically important lipids containing molecules: • Fats • Phospholipids • Steroids

  2. Fats • Structure • Composed of two different molecules bonded by ester linkage • fatty acid & glycerol • - Fatty acid Hydrocarbon chain with a carboxyl group at one end • Glycerol • Three-carbon alcohol • Each carbon attached to hydroxyl group Try to Draw

  3. LE 5-11a Fatty acid (palmitic acid) Glycerol Dehydration reaction in the synthesis of a fat

  4. Ester linkage LE 5-11b Fat molecule (triacylglycerol)

  5. Properties of Fats • Hydrophobic • H2O molecules form hydrogen bonds with each other and EXCLUDE fatty acid chains--> Fats separate from H2O (like oil & vinegar) Fatty acids variable chain length (often 16-18 carbons)

  6. Saturated fat - refers to saturated fatty acid chains - carbons contains maximum number of hydrogens - results in 100% single bonds (no double bonds) - more linear, packs tightly to form solid Tend to be from animals

  7. Saturated or unsaturated? Ester linkage LE 5-11b Fat molecule (triacylglycerol)

  8. Butter LE 5-12a Stearic acid Saturated fat and fatty acid.

  9. Unsaturated fat -contains unsaturated fatty acids -carbon-carbon double bonds (>1) -irregular hydrocarbon conformation -poor packing -forms liquids (oils) at room temperature Tend to be from plants and fish

  10. Olive oil Other liquid fats (unsaturated)? LE 5-12b Oleic acid cis double bond causes bending Unsaturated fat and fatty acid.

  11. Phospholipids • Structure • two fatty acids bonded to glycerol through ester linkage • Phosphate bonded to third hydroxyl group of glycerol • Fatty acids= Hydrophobic tail • Phosphate and other groups= hydrophilic head Draw schematic

  12. LE 5-13 Choline Hydrophilic head Phosphate Glycerol Hydrophobic tails Fatty acids Hydrophilic head Hydrophobic tails Space-filling model Structural formula Phospholipid symbol

  13. If many phospholipids were mixed in H2O into what structures would they self-assemble? • Micelle (draw) - Detergents • Bilayer (draw) -Cell membranes

  14. Cellular membrane: Phospholipid Bilayer LE 5-14 WATER Hydrophilic head Hydrophobic tails WATER

  15. Steroids • Structure - Hydrophobic molecules made of 4 fused hydrocarbon rings • Examples and Diverse Functions • Cholesterol • Component of animal cell membranes • Building block for steroid sex hormones such as • Estrogen, testosterone, progesterone • High levels--> contribute to heart disease

  16. Cholesterol

  17. estradiol testosterone

  18. Pardon me. Did you miss anything?

  19. Ch 7 Membrane Structure and Function

  20. Cellular membrane -overall functions - Boundary between intracellular compartments, living cells, and abiotic environment • Selectively permeable • Some molecules cross membranes more readily than others

  21. Membrane Structure Predominant constituent: phospholipids • Amphipathic molecules: hydrophobic AND hydrophilic Dispersed protein components Membrane organization and properties described by: Fluid Mosaic Model Singer and Nicolson 1972

  22. Organization of membrane phospholipids LE 7-2 WATER Hydrophilic head Hydrophobic tail WATER

  23. Mosaic: something made of small pieces

  24. Mosaic: Proteins dispersed among phospholipids in membrane: LE 7-3 Hydrophilic region of protein Phospholipid bilayer Hydrophobic region of protein

  25. Freeze-fracture studies of the plasma membrane • Frozen membrane split along the middle of the phospholipid bilayer using a knife • Imaged by EM Supports mosaic part of model

  26. Extracellular layer LE 7-4 Proteins Knife Plasma membrane Cytoplasmic layer Extracellular layer Cytoplasmic layer

  27. The Fluidity of Membranes • Phospholipids move laterally within the bilayer • Some membrane proteins also drift laterally • Rarely does a phospholipid flip-flop transversely across the membrane

  28. LE 7-5a Lateral movement (~107 times per second) Flip-flop (~ once per month) Movement of phospholipids

  29. Effects of Temperature on membranes • Cool temp: membranes switch from fluid to more solid state • Solidification depends on type of lipid • What property of lipids would favor liquid versus solid state?

  30. Degree of saturation of fatty acid tails LE 7-5b Viscous Fluid Saturated hydro- carbon tails Unsaturated hydrocarbon tails with kinks Membrane fluidity

  31. Steroid cholesterol also component of membranes • Tends to moderate effects of temp. on membrane state • At warm temperatures (such as 37°C), restrains movement of phospholipids • At cool temperatures, maintains fluidity by preventing tight packing

  32. LE 7-5c Cholesterol Cholesterol within the animal cell membrane

  33. Movement of membrane proteins Can drift within the bilayer • Proteins much larger than lipids--> move more slowly • Cell fusion studies support fluidity of membrane proteins

  34. LE 7-6 Membrane proteins Mouse cell Mixed proteins after 1 hour Human cell Hybrid cell

  35. Membrane Proteins and Their Functions • Proteins determine most of the membrane’s specific functions • Peripheral membrane proteins • not embedded • attached to extracellular or cytoplasmic surface • Integral membrane proteins • penetrate the hydrophobic core of bilayer • often span the membrane

  36. Fibers of extracellular matrix (ECM) LE 7-7 Glycoprotein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Cholesterol Peripheral proteins Microfilaments of cytoskeleton Integral protein CYTOPLASMIC SIDE OF MEMBRANE

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