Lipids, Biological Membranes and Cellular Transport. 阮雪芬 May/9/2004

Transcription

1 Lipids, Biological Membranes and Cellular Transport 阮雪芬 May/9/2004

2 Outline Introduction Fatty Acids Triacylglycerols Polar lipids Steroids and other lipids Biological membranes Membrane transport Examples of membrane transport

3 Outline Introduction Fatty Acids Triacylglycerols Polar lipids Steroids and other lipids Biological membranes Membrane transport Examples of membrane transport

4 Introduction Fats The principle molecules for energy storage, nonpolar lipids Membrane: polar lipid Give the cell its shape and form and protect its channels and gates to regulate the outside environment

5 Animal Cell Membrane Oxidative metabolism Sorting out newly synthesized proteins Double membrane Contain hydolytic enzyme

6 Outline Introduction Fatty Acids Triacylglycerols Polar lipids Steroids and other lipids Biological membranes Membrane transport Examples of membrane transport

7 The Structures of Two Fatty Acids A saturated acid A unsaturated acid

8 An Amphiphilic Molecule Amphi = both kinds of

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11 Double bond

12 Physical and Chemical Properties of Fatty Acids All soluble in organic solvents, such as alcohol, hexane, and diethy ether. CH 3 (CH 2 ) 10 COOH + NaOH CH 3 (CH 2 ) 10 COO - Na + + H 2 O (a soap)

13 Outline Introduction Fatty Acids Triacylglycerols Polar lipids Steroids and other lipids Biological membranes Membrane transport Examples of membrane transport

14 The Stepwise Addition of Fatty Acids to Glycerols to the Final Stage of a Triacyglycerol 1 3 2

15 Triacyglycerol The primary biological role of the fatty acids is serve as metabolic fuel for cells. The acids are ingested and stored for future energy use in triacyglycerols. Triacyglycerol are nonpolar, hydrophobic molecules.

16 Fats: Trigacylglycerol isolated from animal tissues Oils: Trigacylglycerol mixtures from plant seed and contain mainly unsaturated acids

17 Saponification CH 2 OCR O CHOCR O CH 2 OCR NaOH + H 2 O CH 2 OH RCOO - Na + CHOH + R COO - Na + CH 2 OH R COO - Na + O Triacylglycerols Glycerol Soaps

18 Hydrolysis CH 2 OCR O CHOCR O CH 2 OCR O lipase + 3H 2 O CH 2 OH RCOOH CHOH + R COOH CH 2 OH R COOH

19 Trans fatty acids may increase blood cholesterol levels

20 Anandamide and Chocolate Craving Window on Biochemistry 9.2

21 Biological Properties of Triacylglycerols Two primary biological roles Energy metabolism Insulation Triacylglycerols are present in oily droplets in the cytoplasm of plant and animal cells

22 Animal cells specialized for fat storage Adipocytes

23 Lipase CH 2 OCR O CHOCR O CH 2 OCR O + 3H 2 O CH 2 OH RCOOH CHOH + R COOH CH 2 OH R COOH

24 Nonpolar lipids Beewax

25 Outline Introduction Fatty Acids Triacylglycerols Polar lipids Steroids and other lipids Biological membranes Membrane transport Examples of membrane transport

26 Polar Lipids A class of lipids with chemical structures similar to the triacylglycerols, but quite different in biological function. Two new classes of lipids: Glycerophospholipids Sphingolipids

27 Structural Features of Storage and Membrane Lipids

28 Glycerophospholipids Phosphatic Acid is the foundation molecule for the glycerophospholipids 1,2-diacylglycerol 3-phosphate Phosphoric acid is triprotic It is able to react with up to three alcohol moieties to form mono-, di-, triesters. Two structural features in the glycerophospholipids: a polar head and nonpolar tails

29 Sphingolipid The fuondation molecule for the sphingolipid is sphingosine Has two functional groups: amino and hydroxyl Fatty acid Insulate nerve axons

30 Liposome and Micelle Liposome: a hollow spherical lipid bilayer Micelle: present in only minor quantities

31 The polar lipid constituents of cell membranes The Lipid Bilayer

32 Bilayers

33 Outline Introduction Fatty Acids Triacylglycerols Polar lipids Steroids and other lipids Biological membranes Membrane transport Examples of membrane transport

34 The Structure of Steroids

35 Cholesterol and Cholesteryl Ester A Polar head Nonpolar tail Fatty acid A

36 The cholesterol molecule is derived from units of five carbons called isoprene

37 Steroid Hormone Female sex hormone Male sex hormone Regulator of glucose metabolism

38 Bile Salts Are stored in the gallbladder and secreted into the intestines to help solubilize, digest, and absorb dietary fats

39 Phytosterols To lower serum cholesterol by blocking dietary cholesterol cholesterol and cholesterol secreted in the bile from being absorbed by the intestine Structures very similar to cholesterol

40 Terpenes The lipid class of terpenes includes all molecules biosynthesized from the isoprenes Many of these compounds provide the colors and odors associated with plants.

41 Terpenes The source of the orange color in carrots Citrus fruits An intermediate in cholesterol A plant growth hormone Tomato skin

42 Eicosanoids A class of lipids characterized by their localized, hormonelike activities and very low cellular concentrations. The biological properties Influence on reproductive functions Regulation of blood clotting and blood pressure The generation of inflammation, fever, and pain associated with injury and diseases Regulation of temperature and the sleep=wake cycle in humans and animals.

43 Eicosanoids Promotes physiological sleep Aspirin and ibuprofen 20-carbon polyunsaturated fatty acid Induce wakefulness Cause the contraction of smooth muscle Facilitate the formation of blood clots

44 Fat-soluble Vitamins

45 Two Insect Pheromones Housefly Honeybees

46 Electron Carriers Ubiquinone: in animals Plastoquinone : in plants Menaquinone: in bacteria

47 Outline Introduction Fatty Acids Triacylglycerols Polar lipids Steroids and other lipids Biological membranes Membrane transport Examples of membrane transport

48 Biological Roles of Membranes As a physical barrier As a selective filter As energy transduction systems

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50 Lipid Bilayer As a selective, permeable barrier for transport of molecules. Fluidity

51 Distribution of Lipids in the Two Monolayers of the Human Erythrocyte

52 Cholesterol 3% in mitochondrial membrane 38% in typical plasma membrane Never found in plant Stiff and more rigid than other polar lipids

53 Membrane Portiens a, b, c: Integral proteins As transport proteins d, e: Peripheral proteins As receptor sites and enzymes

54 The Fluid-mosaic Model for Biological Membranes S. Jonathan Singer and Garth Nicholson in 1972 suggested this model

55 Outline Introduction Fatty Acids Triacylglycerols Polar lipids Steroids and other lipids Biological membranes Membrane transport Examples of membrane transport

56 Membrane Transport Passive transport Simple diffusion Facilitated diffusion Active transport Ion pumping

57 Simple diffusion Fatty acids Important gases CO 2, N 2, O 2, CH 4 Passive Transport

58 Passive Transport Facilitated diffusion Sugar Amino acids

59 Active Transport of Solutes Need energy

60 Outline Introduction Fatty Acids Triacylglycerols Polar lipids Steroids and other lipids Biological membranes Membrane transport Examples of membrane transport

61 Glycophorin A of the Erythrocyte 131 amino acid residues and 16 oligosaccharide groups 30 hydrophobic amino acid residue Alpha-helix Membrane

62 Glucose Permease of Erythrocyte Membrane

63 The Kinetics of the Glucose Permease Transport Process Similar to kinetics of enzyme action

64 The Proposed Arrangement of Glucose Permease in the Erythrocyte Membrane 492 amino acids 25 domains: 12 hydrophobic and 13 hydrophilic

65 Transport of Sodium and Potassium Ions by Sodium-Potassium ATPase Need energy Pump

66 Patch Clamp Technique

67 Ion -Channels

68 Exercises 9.1 a, b, c, h, i, j, k, l, m, q, r, t