1. Bettelheim, Brown, Campbell and Farrell Chapter 21
Lipids
Bettelheim, Brown, Campbell and Farrell
Chapter 21

2. Lipids
Lipids: a heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility properties
insoluble in water, but soluble in organic solvents including diethyl ether, dichloromethane, and acetone

3. Functional Classification of Lipids
Storage of energy in animals
Membrane components
Lipid bilayer
Messengers
Primary: Hormones
Secondary: mediate hormonal response
prostaglandins, thromboxanes, etc.

4. Lipids
Lipids include
fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, and glycolipids
lipid-soluble vitamins
prostaglandins, leukotrienes, and thromboxanes
cholesterol, steroid hormones, and bile acids

5. Structural Classification of Lipids
Simple Lipids
Fatty acids, waxes
Complex Lipids
Multiple components
Steroids
Prostaglandins, Thromboxanes and Leukotrienes

6. Fatty Acids
Fatty acid: an unbranched-chain carboxylic acid derived from hydrolysis of animal fats, vegetable oils, or membrane phospholipids
Usually unbranched chain with carbons
EVEN number of carbons
May be saturated or unsaturated (C=C)
Unsaturated generally have cis double bonds
Unsaturated fatty acids have lower melting points than their saturated fatty acids
Most abundant are palmitic acid (16:0), stearic acid (18:0), and oleic acid (18:1)

8. Fatty Acid Notation (18:0) = 18 C and no double bonds
(18:1) = 18 C and one double bond
(18:3) = 18 C and three double bonds

9. Table 20.1, p.496

10. Fatty Acids

11. Waxes
High molecular-weight esters
46 C total for triacontyl palmitate

12. Fats and Oils Contain glycerol and fatty acids Glycerol is triol
Combined with ester
bonds

13. Triglycerides
Triglyceride (triacylglyceride): an ester of glycerol with three fatty acids

14. Example of triglyceride

15. Triglycerides
Triglyceride (triacylglyceride): an ester of glycerol with three fatty acids

16. Triglycerides Physical properties depend on the fatty acid components
More carbons: higher melting point
More saturated (fewer C=C): higher melting point
Oils:
More unsaturated fatty acids
Liquid at room temperature
Fats:
Primarily saturated fatty acids
Semisolids or solids at room temperature

17. Triglycerides Melting points related to 3-D shape of triglyceride
Saturated fatty acids can pack closely together
More London dispersion forces between chains
Higher melting points (above room temperature)
Unsaturated fatty acids have cis double bonds
Bend in chain prevents close packing
Fewer London dispersion forces between them
Lower melting points (below room temperature)

18. Packing of Saturated vs Unsaturated Fatty Acids

19. Hydrogenation
Can convert liquid oil to solid fat by adding H2 to double bonds by using H2/catalyst
Can control hardening to produce fats of a desired consistency
Examples: Crisco, Spry, Dexo, etc.
Margarine produced by partial hydrogenation of polyunsaturated oils derived from corn, cottonseed, peanut, and soybean oils

20. Hydrogenation of triglyceride

21. Iodine or Bromine Test for Unsaturation
Add Br2 (or I2) to C=C.
The more Br2 or I2 you add, the greater the number of double bonds in the fat or oil
Iodine number is a measure of unsaturation.

22. Soaps
Natural soaps are prepared by boiling lard or other animal fat with NaOH, in a reaction called saponification (Latin, sapo, soap)

23. Soaps Soaps clean by acting as emulsifying agents
their long hydrophobic hydrocarbon chains cluster so as to minimize their contact with water
their polar hydrophilic carboxylate groups remain in contact with the surrounding water molecules
driven by these two forces, soap molecules spontaneously cluster into micelles

24. Soaps
Soaps form water-insoluble salts (scum) when used in water containing Ca2+, Mg2+, and Fe3+ ions (hard water)

26. Complex Lipids Phospholipids Glycolipids
contain an alcohol, two fatty acids, and a phosphate ester
in glycerophospholipids, the alcohol is glycerol
in sphingolipids, the alcohol is sphingosine
Glycolipids
complex lipids that contain a carbohydrate

27. Fig 20.1, p.501

28. Complex Lipids

29. Membranes
Complex lipids form the membranes around cells and small structures within cells
In aqueous solution, complex lipids form into a lipid bilayer, with a back-to-back arrangement of lipid monolayers
polar head groups are hydrophilic and point to aqueous environment
nonpolar tails are hydrophobic and are inside the bilayer
hydrophobic interactions drive bilayer formation
Rigidity of membrane depends on whether fatty acid tails are saturated or unsaturated

30. Membrane bilayer
Hydrophilic head outside
Hydrophobic tails inside

31. Membrane Rigidity Depends on nature of fatty acid tails
Saturated fatty acids = more rigid
Unsaturated fatty acids = less rigid
Reindeer legs
Near foot membranes have different fatty acid composition than in other parts of animal

32. Fig 20.1, p.501

33. Membrane bilayer
Hydrophilic head outside
Hydrophobic tails inside

34. Fluid Mosaic Model

35. Transport across membrane
Passive transport
Gap junctions—6 proteins make a central pore
Small molecules pass through pores
Ions, sugars, amino acids, nucleotides
Large molecules can’t pass through
Pore can be open or twisted shut
Facilitated transport
Interaction between transporter and transported molecule
Active transport—
Ions transported against concentration gradient
Energy expended to change shape of protein and transport ion across membrane

36. Transport across membranes
Active transport—
Ions transported against concentration gradient
Energy expended to change shape of protein and transport ion across membrane
Polar compounds transported via specific transmembrane channels.

37. Complex lipids found in membranes Simple lipids
Fig 20.1, p.501

38. Glycerophospholipids
Glycerophospholipids (phosphoglycerides) are the second most abundant group of naturally occurring lipids
found in plant and animal membranes, which consist of 40% -50% phosphoacylglycerols and 50% - 60% proteins
Major phosphoacylglycerols are derived from phosphatidic acid
glycerol + 2 fatty acids + phosphate
Most abundant fatty acids in phosphatidic acids are palmitic (16:0), stearic (18:0), and oleic (18:1)

39. Glycerophospholipids
A phosphatidic acid
Fatty acid attached to C-2 is always unsaturated
Can also add small alcohol to the phosphate to make a glycerophospholipid

40. Glycerophospholipids

41. Glycerophospholipids
a lecithin

42. Glycerophospholipids
Phosphatic acid
Glycerol, 2 fatty acids, phosphate
Lecithins
Glycerol, 2 fatty acids, phosphate, choline
Cephalins
Glycerol, 2 fatty acids, phosphate, ethanolamine or serine

43. Sphingolipids Found in the myelin sheath of nerve axons
Sphingomyelin deterioration found in MS
Contain sphingosine, a long-chain aminoalcohol

44. Glycolipids Glycolipid: complex lipid that contains a sugar
Sugar is glucose or galactose
Cerebrosides found in brain and nerve synapses

45. Steroids
Steroids: a group of plant and animal lipids that have a steroid ring structure

46. Cholesterol
Cholesterol is the most abundant steroid in the human body, and also the most important
Component in animal plasma membranes
Precursor of all steroid hormones and bile acids

47. Lipoproteins
Schematic of a low-density lipoprotein

48. Lipoproteins
Cholesterol, along with fats, are transported by lipoproteins

49. Lipoproteins Protein has a higher density than lipids do
HDL (high density lipoprotein)
Have higher protein to lipid ratio
LDL (low density lipoprotein)
have lower protein to lipid ratio

50. Cholesterol Transport— from liver to peripheral cells
Transport from the liver starts with VLDL (55 nm)
Carried in plasma
Density increases as fat is removed
VLDL becomes LDL (22 nm)
LDL stays in the plasma for about 2.5 days
LDL carries cholesterol to cells, where specific LDL receptors (coated pits) bind it
LDL is taken into cells where enzymes liberate free cholesterol and cholesteryl esters

51. Cholesterol Transport— from peripheral cells to liver
HDL transport cholesterol from peripheral tissues to the liver and also transfer cholesterol to LDL
Free cholesterol in HDL is converted to cholesteryl esters (while in serum)
HDL binds to the liver cell surface and transfers its cholesteryl esters to the cell
Cholesterol esters are used for the synthesis of steroid hormones and bile acids
after HDL has delivered its cholesteryl esters to liver cells, it reenters circulation

52. Cholesterol forms plaque deposits on inside of blood vessels (atherosclerosis)
Narrows blood vessel diameter
Lowers blood flow
Can lead to heart attack, stroke, kidney disfunction or other problems

53. Levels of LDL and HDL Most cholesterol is carried by LDL
Normal plasma levels are 175 mg/100 mL
LDL is removed from circulation if there are enough LDL receptors on cells
Number of LDL receptors controlled by feedback mechanism
High cholesterol inside cell suppresses receptor synthesis
Hypercholesterolemia: not enough LDL receptors
High plasma cholesterol levels (up to 680 mg/100 mL)

54. Levels of LDL and HDL
High LDL together with low HDL is a symptom of faulty cholesterol transport and a warning of possible atherosclerosis
Serum cholesterol level controls cholesterol synthesis in the liver
High serum cholesterol results in low synthesis of cholesterol in liver, and vice versa
Statin drugs inhibit the synthesis of cholesterol

55. Steroid Hormones Androgens: male sex hormones
synthesized in the testes
responsible for the development of male secondary sex characteristics

56. Steroid Hormones
Among the synthetic anabolic steroids are

57. Steroid Hormones Estrogens: female sex hormones
synthesized in the ovaries
responsible for the development of female secondary sex characteristics and control of the menstrual cycle

58. Steroid Hormones
Progesterone-like analogs are used in oral contraceptives

59. Steroid Hormones Glucorticoid hormones
synthesized in the adrenal cortex
regulate metabolism of carbohydrates
involved in the reaction to stress
decrease inflammation

60. Bile Salts Bile salts, the oxidation products of cholesterol
synthesized in the liver, stored in the gallbladder, and secreted into the intestine where they emulsify dietary fats and aid in their absorption and digestion

61. Prostaglandins
Prostaglandins: a family of compounds that have the 20-carbon skeleton of prostanoic acid

62. Prostaglandins
Prostaglandins are synthesized in response to specific physiological triggers
Made from membrane-bound 20-carbon polyunsaturated fatty acids such as arachidonic acid

63. Prostaglandins

64. COX Enzymes COX enzyme occurs in two forms
COX-1 catalyzes the normal physiological production of prostaglandins
COX-2 is responsible for the production of prostaglandins in inflammation
when a tissue is injured or damaged, special inflammatory cells invade the injured tissue and interact with tissue cells
interaction activates COX-2 and prostaglandins are synthesized

65. Thromboxanes Thromboxanes are also derived from arachidonic acid
thromboxane A2 induces platelet aggregation and vasoconstriction
aspirin and other NSAIDs inhibit the synthesis of thromboxanes by inhibiting the COX enzyme

66. Leukotrienes Synthesized from arachidonic acid
occur mainly in leukocytes
produce muscle contractions, especially in the lungs and thereby can cause asthma-like attacks
100 times more potent than histamine
Many new anti-asthma drugs inhibit the synthesis of leukotrienes