1. Chem 150 Unit 5 - Biological Molecules I Lipids
Like organic molecules, biological molecules are grouped into families. There are four major families of biological molecules, including proteins, nucleic acids, carbohydrates, and lipids. The lipids are the subject of this unit. Of these four families, the lipids are the structurally the most diverse. This is because unlike members of the other three families, members of this families do no share a common structural feature, but rather share a common physical property; the are hydrophobic.

2. Introduction Lipids are hydrophobic, nonpolar molelcules.
They are soluble in nonpolar solvent.
They are insoluble in polar solvents, such as water
They are isolated from the other biological molecules by extracting them with nonpolar solvents.

3. Introduction The types of lipids that we will look at include.
Fatty Acids
In the carboxylic acid family
Waxes
Fatty Acids + Alcohols
Triglycerides
3 Fatty acids + glycerol
Phospholipids and glycolipids
2 fatty acids + glycerol + phosphate + X
Steroids
Derivatives of cholesterol
Eicosanoids
Derivatives of the Fatty acid arachidonic acid
Membranes
Formed from phospholipids and glycolipids

4. Fatty Acids Fatty acids contain a carboxylic acid group
This should make them quite polar
However, they also contain a long hydrocarbon tail
Which overall, makes them nonpolar.
nonpolar
polar

5. Fatty Acids Fatty acids typically contain between 12 and 20 carbons
The number is usually always even.
The nonpolar tails interact with London forces.
nonpolar
polar

6. Melting Temperature {°C}
Fatty Acids
Melting points for saturated fatty acids:
Melting Temperature {°C}
No. of Carbons

7. Fatty Acids Some fatty acids contain double bonds unsaturated
monounsaturated
polyunsaturated

8. Fatty Acids
The common fatty acids found in biological systems are shown in Table 8.1 of Raymond.
Describe why linolenic acid is considered an omega-3 fatty acid.
α-linolenic acid is considered and essential nutrient because we are unable to synthesize omega-3 fatty acids de novo. We can synthesize all the other omega-3 fatty acids from α-linolenic acid.
Text
Linolenic acid is one of the omega-3 fatty acids.

9. Melting Temperature {°C}
Fatty Acids
Normally the double bonds are cis
This lowers the melting points for fatty acids containing double bonds.
Melting Temperature {°C}
No. of Double Bonds

10. Fatty Acids
The cis double bonds produce kinks, which disrupt the London forces by preventing the tails from packing close to one another.

11. Fatty Acids
As acids, the carboxylic acid group in fatty acids can react with a base to produce a carboxylate ion
By donating its proton (H+) to the base the fatty acid becomes negatively charged.
We will talk more about acids and bases in Unit 6

12. Fatty Acids
The negative charge makes the polar head portion of the the fatty acid even more more polar and hydrophilic.

13. Fatty Acids
The salts of fatty acids are also called soaps, and are considered amphipathic, meaning they have a part that is very hydrophobic along with a part that is very hydrophilic.
In Unit 3 we discussed how amphipathic molecules form interesting structures when exposed to water.

14. Biochemical Compounds & Their Interactions with Water (Unit 3)
When placed in water, amphipathic molecules, form structures, such as micelles, which attempt to address the conflict.

15. Fatty Acids
The salts of fatty acids are also called soaps, and are considered amphipathic, meaning they have a part that is very hydrophobic along with a part that is very hydrophilic.
In Unit 3 we discussed how amphipathic molecules form interesting structures when exposed to water.

16. Waxes
Waxes are made by combining fatty acids with long chain alcohols.
In Unit 2 we discussed how carboxylic acids react with alcohols to from esters.

17. Alcohols, Carboxylic Acids & Esters (Unit 2)
We look now at three families that are distinguished by a functional group that contains the element oxygen.
Esters
Chemically, esters can be synthesize by reacting a carboxylic acid with and alcohol:
Ethyl propanoate

18. Waxes
Waxes are esters.
14-36 carbons
16-30 carbons

19. came from the fatty acid
Waxes
When two more molecules combine to form a larger molecule, the word residue is used to indicate which molecule that part of the the larger molecule came from.
came from the alcohol
came from the fatty acid

20. Waxes
Waxes are very hydrophobic and are used by plants and animals for protective, water-proof coatings

21. Questions
Draw the skeletal structures for the products formed when beeswax undergoes base-catalzyed hydrolysis (saponification).

22. Reactions Involving Water (Unit 4)
Hydrolysis
Hydrolysis can also be catalyzed using a base (OH-):.
Because one of the products of the hydrolysis is a carboxylic acid, in base catalyzed hydrolysis the base undergoes a second acid/base reaction with the carboxylic acid to produce a carboxylate ion.
The base catalyzed hydrolysis of esters is also called saponification
We will be discussing acids and bases in Unit 6
Show the fumarate reaction using FAD
Show the alcohol dehydrogenase eaction using NADH
Reactions with water
hyrolysis of ester with acid
hydrolysis of ester with base
hydration reaction
dehydration reactions

23. *American Heart Association
Triglycerides
Triglycerides are a storage form of fatty acids in mammals.
Often when blood tests are done, they measure your triglycyeride levels.
High triglyceride levels in the blood are a risk indicator for artherosclerosis.
*American Heart Association

24. Triglycerides
Triglycerides are a combination of three 3 fatty acid molecules with a glycerol molecule.

25. Triglycerides
Glycerol, which is also called glycerin, is an alcohol with three hydroxyl groups.
As with the waxes, the fatty acids can react with the hydroxyl groups to form esters.
Since there are three hydroxyl groups, three fatty acids can react to form three esters.

26. Triglycerides
For triglycerides, all three hydroxyls of the glycerol have a fatty acid residue attached to it.

27. Figure 8.6
from
Raymond

28. Triglycerides
Just as with fatty acids, where the presence of cis double bonds lower the melting points, triglycerides made from unsaturated fatty acids have lower melting points than those made from saturated fatty acids.
Triglycerides from animals tend to have a higher proportion of saturated fatty acids.
Most are solids at room temperature and are called fats.
Examples include: butter, lard and bacon grease
Triglycerides from plants tend to have a higher proportion of unsaturated fatty acids.
Most are liquids at room temperature and are called oils.
Examples include: corn oil, canola oil, peanut oil and olive oil.

29. Triglycerides
Triglycerides as primarily used as a form of stored energy.
This is why when you eat more than you need to meet your energy requirements, the excess energy is stored in the form of fat.
Fat can store almost twice as much energy per gram as carbohydrates and proteins
In mammals the fats are stored in the adipose tissue.
Adipose tissue also functions to protect organs from shock and cold.

30. Triglycerides Reactions that involve triglycerides include:
Hydrogenation
Oxidation
Base-catalyzed hydrolysis (saponification)

31. Transport of fats: VLDL moves triglycerides from liver to tissues.
LDL transfers
cholesterol to
tissues from liver.
HDL carries
cholesterol from
tissues to liver.
Monoglycerides and fatty
acids are absorbed by
intestines - transported
as chylomicrons in lymph
system to blood.-Fat Blocker-Xenical (Alli)
Dietary fat

32. Typical diacylglycerol
Transport of fats:
Fat Blocker-Xenical (Alli)
Typical diacylglycerol

33. Fun Topic !: Fake Fats Side effects?
Olestra: sucrose fatty acid ester(s)
Fat : glycerol fatty acid ester(s)

34. Triglycerides Hydrogenation of triglycerides
This is the same reaction that we saw in Unit 4 with the hydrogenation of alkenes.
Unsaturated fats and oils contain alkenes and can be hydrogenated to produce saturated fats.
Commercially, vegetable oils are often hydrogenated to produce a solid product that has better qualities for making baked goods.
Animal fats, such as butter and lard, which are naturally saturated, can also be used, but unlike the vegetable oils, they come with cholesterol, which is undesirable for health reasons.

35. Oxidation and Reduction (Unit 4)
Hydrogenation
Another type of oxidation/reduction reaction is the hydrogenation reaction:
In this example, an alkene is reduced to an alkane.
This is considered reduction, because the hydrogen is bringing in additional electrons to the molecule.
The alkane that is produced in this reaction is considered “saturated” because it can no longer absorb any more hydrogen atoms.
Show the fumarate reaction using FAD
Show the alcohol dehydrogenase eaction using NADH
Reactions with water
hyrolysis of ester with acid
hydrolysis of ester with base
hydration reaction
dehydration reactions
unsaturated
saturated

36. Triglycerides Hydrogenation of triglycerides
This is the same reaction that we saw in Unit 4 with the hydrogenation of alkenes.
Unsaturated fats and oils contain alkenes and can be hydrogenated to produce saturated fats.
Commercially, vegetable oils are often hydrogenated to produce a solid product that has better qualities for making baked goods.
Animal fats, such as butter and lard, which are naturally saturated, can also be used in baking, but unlike the vegetable oils, they come with cholesterol, which is undesirable for health reasons.

37. Triglycerides Hydrogenation of triglycerides Total hydrogenation
liquid
solid

38. Triglycerides Hydrogenation of triglycerides Partial hydrogenation
liquid
solid

39. Triglycerides Hydrogenation of triglycerides
Partial hydrogenation cab produce trans fats.
Trans fats have been found to lower your HDL (“Good cholesterol”) levels.

40. Triglycerides
Saturated vs Unsaturated Fats

41. Triglycerides
Saturated vs Unsaturated Fats

42. Triglycerides
Saturated vs Unsaturated Fats

43. Triglycerides
Saturated vs Unsaturated Fats

44. Fat (Triacylglyceride)
Triglycerides
Saturated vs Unsaturated Fats
Fat (Triacylglyceride)

45. Triglycerides Oxidation of triglycerides
Unsaturated triglycerides can react with oxygen to produce small change fatty acids another small molecules.
These often do not smell very good
This is what happens when butter goes rancid.
This makes solid fats and oils more stable than liquid oils and is why the solid fats are preferred for deep frying.

46. Triglycerides
Oxidation of triglycerides
These stink !

47. Triglycerides Saponification of triglycerides
Saponification is the base-catalyzed hydrolysis of the ester bonds in a triglyceride.
We also discussed this reaction in Unit 4
This cleaves the esters back into carboxylic acids (fatty acids) and an alcohol (glycerol).
Because the reaction is base-catalyzed, the base also reacts with the carboxylic acids to from carboxylate ions
We saw this on an earlier slide

48. Reactions With Water (Unit 4)
Hydrolysis example:
The base catalyzed hydrolysis of fats produces soap and glycerol
Fat

49. Reactions With Water (Unit 4)
Hydrolysis example:
The base catalyzed hydrolysis of fats produces soap and glycerol
Soap
Glycerol

50. Phospholipids and Glycolipids
Phospholipids and Glycolipids are the stuff that biological membranes are made of.
Like the soaps, these molecules are highly aphipathic, and when mixed with water spontaneously form membranes that are described as lipid bilayers.

51. Phospholipids and Glycolipids
Soaps form
Micelles
Phospholipids form
Lipid Bilayers

52. Phospholipids and Glycolipids
Phospholipids and Glycolipids are the stuff that biological membranes are made of.
Like the soaps, these molecules are highly aphipathic, and when mixed with water spontaneously form membranes that are described as lipid bilayers.

53. Phospholipids and Glycolipids
Phosphospholipids
There a are two types of phospholipids
Glycerophospholipids

54. Phospholipids and Glycolipids
Phosphospholipids
There a are two types of phospholipids
Sphingolipids

55. Phospholipids and Glycolipids
Phosphospholipids
The Glycerophospholipids have a structure similar to triglycerides, with one of the fatty acids replaced with a phosphate.
There is usually an additional alcohol attached to the other side of the phosphate

56. Phospholipids and Glycolipids
Phosphospholipids
The Glycerophospholipids have a structure similar to triglycerides, with one of the fatty acids replaced with a phosphate.
phosphoester
bonds

57. Phospholipids and Glycolipids
Phosphospholipids
The Glycerophospholipids have a structure similar to triglycerides, with one of the fatty acids replaced with a phosphate.
“Phosphotidyl-”
refers to everything
but the X

58. Phospholipids and Glycolipids
Phosphospholipids
Phospholipids are used commercially as emulsifying agents.
An emulsifying agent stabilizes an emulsion.
An emulsion is a colloidal suspension of one liquid in another.
An example is mayonnaise, which is a colloidal suspension of oil and water.
Lecithin, which is another name for the phospholipid phosphotidylcholine, is used as an emulsifying agent in mayonnaise and other prepared foods.

59. Phospholipids and Glycolipids
Phosphospholipids
The sphingolipids function similarly to the glycerophospholipids, but structurally they are different.
There is not glycerol core
The glycerol and one of the fatty acids found in glycerophospholipids is replaced with a molecule called sphingosine.

60. Phospholipids and Glycolipids
Phosphospholipids
The sphingolipids are found in the myelin membranes that insulate the nerve cells.
Some sphingolipids use sugars for the alcohol portion of the molecule
These are called glycolipids.

61. Steroids
Steroids are a type of lipid that is not derived form a fatty acid.
They are based instead on a system of five cycloalkane rings that are fused together.

62. Steroids
Steroids are a type of lipid that is not derived form a fatty acid.
They are based instead on a system of five cycloalkane rings that are fused together.

63. Note the fused ring system
Steroids
Cholesterol is the steroid that used as the starting point for the synthesis of other steroids.
Note the fused ring system

64. Steroids Cholesterol is only found in animals
Besides being used to synthesize the other steroids, cholesterol is dissolved in membranes to keep them fluid.
Plants use the alternative strategy of using polyunsaturated fatty acids to make their phospholipids.

65. Lipoproteins
Lipoproteins are used to transport the water insoluble lipids such as triglycerides, phospholipids and cholesterol, in the blood.
Lipoproteins contain lipids and proteins.
They include:
Chylomicrons transport primarily triglycerides from the digestive track.
LDLs (low density lipoproteins) transport cholesterol, triglycerides and phospholipids from the liver to other tissues.
HDLs (high density lipoproteins) transport cholesterol and phospholipids back to the liver.

66. Lipoproteins
The HDL and LDL levels in the blood can be used to assess ones risk for atherosclerosis.
High levels of HDL is considered good
This is why HDL is sometimes referred to as “good cholesterol”
> 40 mg/dL is good.
High levels of LDL is considered bad
This is why LDL is sometimes referred to as “bad cholesterol”
> 100 mg/dL is bad.

68. Eicosanoids
Eicosanoids are derived from arachidonic acid:

69. Membranes
Fluid mosaic model

70. Membranes
Transport across membranes

71. The End