1. Biochemistry Sixth Edition
Berg • Tymoczko • Stryer
Chapter 12:
Lipids and Cell Membranes
Copyright © 2007 by W. H. Freeman and Company

2. Lipids Classified by solubility, not structure.
Lipids are any molecules that can be extracted from cells using nonpolar organic solvents.
Lipids are non-polar molecules and are not water soluble although some are amphipathic.

3. Lipid Classes Triglycerides (triacylglycerols)
Glycerol based phospholipids
Sphingosine derivatives: sphingomyelins and gangliosides
Steroids/sterols: cholesterol (C27), bile acids (C24), adrenocortical hormones (C21), and sex hormones (C19 & C18)
Eicosinoids: prostaglandins, thromboxanes, leucotrienes and prostacyclins
Fat-soluble vitamins (pg 424)

4. Triacylglycerol (triglyceride)
Triglyceride (as shown below) is derived from glycerol plus one molecule each of palmitic acid, oleic acid, and stearic acid, the three most abundant fatty acids.
A very non-polar molecule (storage fat)

5. Triacylglycerol
Physical properties of triglycerides depend on the fatty acid components.
the melting point increases as the number of carbons in the hydrocarbon chain increases and as the number of double bonds decrease.
triglycerides rich in unsaturated (cis double bonds) fatty acids are generally liquid at room temperature and are called oils.
triglycerides rich in saturated fatty acids are generally semisolids or solids at room temperature and are called fats.

6. Fatty Acids Naturally occuring components of
triacylglycerols and phospholipids

7. Naming Fatty Acids
omega end (w) carboxyl end (1)

9. Table of Fatty Acids   

10. Phospholipids
Phospholipids are the second most abundant group of naturally occuring lipids.
they are found almost exclusively in plant and animal membranes. Membranes vary in the lipid vs protein content depending upon function.
the most abundant phospholipids are derived from phosphatidic acid, a molecule in which glycerol is esterified with two molecules of fatty acid and one of phosphoric acid.
a second class of phospholipids are the sphingomyelins derived from N-acylsphingosine (ceramide) and a phosphate.

11. Phosphatidic Acid
phosphate
Glycerol residue

12. Glycerophospholipid cartoon
Tail – nonpolar
An amphipathic structure
Head-polar

13. Head Pieces

14. Glycerophospholipids

15. Sphingophospholipids
PalmitoylSCoA + Serine    Sphingosine
Trans db
Trans db

16. Ceramide phosphate N-acylsphingosine-P (ceramide phosphate)
the N-acyl fatty acid is usually unsaturated.
the alcohol normally attached to the phosphate is choline. C H 2 - O P OH N
from serine
from palmitic acid
stearic acid
Trans db

17. Glycolipids (no phosphate)
(Ceramide + glucose or galactose)

18. Glycolipids A complex carbohydrate Gangioside
(Ceramide + a complex carbohydrate)

19. Isoprenoids & the Sterol Family
Isoprenoids are derived from isopentenyl-PP (related to 5-carbon isoprene). Compounds include the terpenes, sterols and fat soluble vitamins.
Sterol Family:
Cholesterol: (C27) Parent molecule and a membrane component
Bile acid salts: (C24) Emulisfy fats for digestion
Adrenocortical Hormones & Progesterone: (C21) Communication
Sex Hormones: Male (C19) and Female (C18)

20. Cholesterol, C27

21. Bile acids, C24

22. C21, C19 and C18
Adrenocortical
Hormone
Sex Hormones
Male
Female

23. Eicosanoids Prostaglandins Prostacyclins, Thromboxanes, Leucotrienes,
Cis - D5, D8, D11, D14 -
eicosatetraenoic acid
Prostaglandins
Prostacyclins, Thromboxanes,
Leucotrienes,

24. Eicosanoids

25. Eicosanoids

26. Lipid Aggregation
Lipids aggregate to form large non-covalent assemblies.
Micelles are spontaneously formed by fatty acids to provide stabilization in aqueous media.
Phospholipids spontaneously for lipid bilayers. The non-polar tails associate with each other and the polar heads interact with water.
Singer & Nicolson proposed the fluid-mosaic membrane model to incorporate proteins and provide functionality.

27. Tail (nonpolar) Head (Polar)
Similar structures

28. Soap Micelle (cross section)
Fatty acid salts
Non-polar inside; Polar outside

29. Lipid Biayer Cartoon
Phospho lipids
Non-polar inside; Polar surface

30. Space Filling Model
Close pack with saturated sidechains (less fluid)

31. Space Filling Model
Packing disrupted by unsaturated sidechains (more fluid)

32. Liposome (Lipid vesicle)

33. Spontaneous formation of
liposomes
Trapping Glycine inside of liposomes

34. Membrane Permeability
Low permeability for ions. Small non-polar molecules (O2, CO2, HOH) pass more easily.

35. Integral (a,b,c) and peripheral (d,e) Proteins

36. Bacteriorhodopsin (a strands)

37. Porin (b strands)
Permits free transport of small molecules.

39. Diagonal lines show hydrogen bonding between anti-parallel strands.
Non-polar residues are in yellow.

40. Protein Domain Anchor

41. Membrane Anchors
Mannose
NAcGlc

43. Glycophorin in red cells

44. Hydropathy Plot

46. Fluid Mosaic Model

47. Fluid Mosaic Model

48. Membrane Composition

49. Inner and Outer Leaflets

50. Membrane Diffusion Membrane components are fluid.
The two sides are assymetric.

51. Phase Transition Temperature

53. Transition Temperatures

54. Fat Soluble Vitamins

55. Saturated

56. Unsaturated (cis)

57. Lipoproteins

58. Endocytosis

59. Biochemistry Sixth Edition
Berg • Tymoczko • Stryer
End of Chapter 12
Copyright © 2007 by W. H. Freeman and Company