1. Lipids Prof. Dr. Suat Erdoğan EBN School of Medicine
Medical Biochemistry Department
October 2013

2. Outline Description of lipids Function of lipids Fatty acids
Triglycerides
Cholesterol
Steroids

3. Lipids
Lipids (or fats) are a heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility properties.
They are insoluble in water, but soluble in nonpolar solvents, including ether, chloroform, benzene and acetone.

4. Major lipids
Lipids may be polar or nonpolar (amphipatic). Polar lipids have limited solubility in water because they are amphipatic.
Major lipids include
triacylglycerols, phosphodiacylglycerols, sphingolipids, glycolipids, lipid-soluble vitamins, and prostaglandins
cholesterol, steroid hormones, and bile acids

5. Properties of Lipids Do not readily dissolve in water
Fats are solid at room temperature
Oils are liquid at room temperature
Triglycerides are the main form of lipids in food and body (storage)
Energy dense (9 kcal/g)

6. Functions of Lipids Provide energy Efficient storage of energy
Insulation
Protection
Transport fat-soluble vitamins
Membrane components
Satiety
Flavor and mouth feel

7. Provide and storage of energy
In the body, fat serves as an efficient source of energy (ATP), both directly and potentially when stored in adipose tissue.

8. Fat cells in the body
The fat is stored in living cells, called fat cells (= adipocyte). Adipocytes makes adipose tissue.

9. Isolation
Fats serves as a thermal insulator in the subcutaneous tissues and around certain organs, and
Nonpolar lipids act as electrical insulators allowing rapid propagation of depolarization waves along myelinated nerves.

11. Protection
Below the dermis lies a layer of fat that helps insulate the body from heat and cold, provides protective padding, and serves as an energy storage area.

12. Transport fat-soluble vitamins
Combinations of fat and protein (lipoproteins) are important cellular constituents, occurring both in the cell membrane and in the mitochondria within the cytoplasm, and serving also as the means of transporting lipids in the blood.

13. Membrane components
Membrane lipids are a group of compounds (structurally similar to fats and oils) which form the double-layered surface of all cells. The three major classes of membrane lipids are phospholipids, glycolipids, and cholesterol.

14. Satiety
Lipids suppress food intake when present in the small intestine of both humans and animals.

15. Flavor and mouth feel
Fats have little taste, but contribute mouth feel and carry odorants.
Fat has a major influence on the sensory perception of food products. Fats enhance the taste and acceptability of foods, and lipid components largely determine the texture, flavor and aroma of foods.

16. Lipids are classified as simple and complex
1. Simple lipids: esters of fatty acids with various alcohols.
Fats: esters of fatty acids with glycerol. A fat in the liquid state is known as oil.
Waxes
2. Complex lipids: esters of fatty acids containing groups in addition to an alcohol and fatty acids.
Phospholipids
Glycolipids
Other complex lipids

17. Fatty acids
Fatty acids occur mainly as esters in natural fats and oils but do occur in the unesterified form as free fatty acids (FFA), a transport form found in the plasma.
The fatty acid chain may be saturated (containing no double bonds) or unsaturated (containing one or more double bonds). Unsaturated fatty acids may be further subdivided as follows:
Monoansaturated acids, containing one double bond (oleic acid).
Polyunsaturated acids containing two or more double bonds (linoleic acid, arachidonic acid).

21. Saturated fatty acid structure
H H H H H H H H H H H H H H H H H O
H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-C-OH
H H H H H H H H H H H H H H H H H
omega end alpha end
degree of saturation
Stearic acid: C18H38O2

23. Saturated fatty acids Lauric acid (12 C) Myristic acid (14 C)
Palmitic acid (16 C)
Stearic acid (18 C)
Arachidic acid (20 C)

25. Unsaturated fatty acids
Palmitoleic acid (16:1)
Oleic acid (18:1)
Linoleic acid (18:2)
-Linolenic acid (18:3)
-Linolenic acid (18:3)
Arachidonic acid (20:4)
16:1 mean: a fatty acid contains 16C and 1 double bond in the structure
Colored in red demonstrates essential fatty acids.

26. Deficiency of essential fatty acids
Essential fatty acid deficiency results in dermatitis.
Clinical signs of essential fatty acid deficiency include a dry scaly rash, decreased growth in infants and children, increased susceptibility to infection and poor wound healing.

28. Monounsaturated Fatty Acid Structure
H H H H H H H H H H H H H H H O
H-C--C--C--C--C--C--C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H H H H H H H
omega end alpha end
One double bond

29. Polyunsaturated Fatty Acid Structure
H H H H H H H H H H H H H O
H-C--C--C--C--C--C=C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H H H H H H H
omega end alpha end
> 2 double bonds

30. Essential Fatty Acid- Omega-6 (linoleic acid)
H H H H H H H H H H H H H O
H-C--C--C--C-- C--C =C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H H H H H H H
omega end alpha end
1st double bond is located on the 6th carbon from the omega end

31. Omega-6 (linoleic) fatty acid
Found in vegetable oils
Only need ~ 1 tablespoon a day
Arachidonic acid can be made from omega-6
Metabolized to form eicosanoids

32. Essential Fatty Acid- Omega-3 (linolenic acid)
H H H H H H H H H H H H H H H H H O
H-C--C--C=C--C--C =C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H
omega end alpha end
1st double bond is located on the 3rd carbon from the omega end

33. Omega-3 (linolenic) fatty acid
Primarily from fish oil
Also found in canola or soybean oil
Metabolized to form eicosanoids
Recommend intake of ~2 servings of fish per week.

34. Essential Fatty Acids Must be eaten
Body can only make double bonds after the 9th carbon from the omega end.
Needed for immune function, vision, cell membrane, and production of hormone-like compounds.

35. Signs and Symptoms of Essential Fatty Acids Deficiency
Itchy skin
Diarrhea
Infections
Retarded growth and wound healing
Anemia

36. Fats

37. Triglycerides (=triacylglycerol)
Triglycerides are the main storage forms of fatty acids.
Triglycerides are esters of the alcohol glycerol and fatty acids.

38. Triglyceride synthesis
H--C--OH O
HO-C-R +
H O
H--C--O--C--
R + H2O
R + H20
(Ester bond)
Glycerol FA’s Triglyceride + 3 H20

39. Triglyceride synthesis
H--C--OH
Fatty Acid
H O
H--C--O--C-- O H
Fatty Acid +
Fatty Acid
Fatty Acid
esterification/reesterification
desterfication

40. Trans and cis fatty acids

45. Phospholipids
Phospholipids are a class of lipids that are a major component of all cell membranes as they can form lipid bilayers. Phospholipids contain a diglyceride, a phosphate group and choline.
Built on a glycerol backbone
Has at least one fatty acid replaced with phosphorus containing compound
Found in body
Synthesized by the body as needed

46. Structure of phospholipids

47. Functions of Phospholipids
Makes up cell membrane
Eicosanoid synthesis
Emulsifier
Bile acids
Lecithins

48. Emulsifier Hydrophilic end (attracts water)
Hydrophobic end (attracts lipid)

49. Emulsification
Emulsification refers to the process of dispersing a substance such as oil in an emulsion. It also refers to the process of converting two or more immiscible liquids into an emulsion. During this process, large fat globules are broken down into smaller, evenly distributed particles.

50. Glycolipids
Glycolipids are lipids with a carbohydrate attached to an -OH of the lipid. Their role is to provide energy and also serve as markers for cellular recognition.

51. Sterols
Sterols, also known as steroid alcohols, are a subgroup of the steroids and an important class of organic molecules. They occur naturally in plants and animals, with the most familiar type of animal sterol being cholesterol. Cholesterol is vital to animal cell membrane structure and function and a precursor to fat-soluble vitamins and steroid hormones.
A multi-ringed structure
Do not have a glycerol backbone
Do not readily dissolve in water

52. Functions of Cholesterol
Essential component of cell membrane
Produced by the liver
Found only in animal products
Forms important hormones
Estrogen, testosterone, vitamin D
Precursor to bile acids

54. Androgens Androgens - male sex hormones synthesized in the testes
responsible for the development of male secondary sex characteristics

55. Estrogens Estrogens - female sex hormones synthesized in the ovaries
responsible for the development of female secondary sex characteristics and control of the menstrual cycle

56. Eicosanoids A group of hormone-like compounds
Regulates blood pressure, childbirth, clotting, immune responses, inflammatory responses, & stomach secretions
By-pass the blood stream and work in the area of origin

57. Eicosanoids Have Different Effects
Omega-6 eicosanoids; archidonic acid
increase blood clotting
increase inflammatory responses
Omega-3 eicosanoids
decrease blood clotting
reduce heart attack
excess may cause hemorrhagic stroke
Eicosanoid has different effect on different tissues.

59. Prostaglandins
Prostanoids are a subclass of eicosanoids consisting of the prostaglandins (mediators of inflammatory and anaphylactic reactions), the thromboxanes (mediators of vasoconstriction), and the prostacyclins (active in the resolution phase of inflammation.)

60. Prostaglandins
Prostaglandins are not stored in tissues as such, but are synthesized from membrane-bound 20-carbon polyunsaturated fatty acids (arachidonic acid) in response to specific physiological triggers

61. Prostaglandins
Research on the involvement of PGs in reproductive physiology has produced several clinically useful derivatives
15-Methyl-PGF2 is used as a therapeutic abortifacient

62. Leukotrienes Leukotrienes: derived from arachidonic acid
found in white blood cells (leukocytes)
an important property is constriction of smooth muscles, especially in the lungs

63. Thromboxanes derived from arachidonic acid
contain a four-membered cyclic ether within a six-membered ring
induce platelet aggregation and smooth muscle contraction

64. What are lipoproteins?
A lipoprotein is a biochemical assembly that contains both proteins and lipids. The lipids or their derivatives may be covalently or non-covalently bound to the proteins. Examples include the high density (HDL) and low density (LDL) lipoproteins which enable fats to be carried in the blood stream, the transmembrane proteins of the mitochondrion and the chloroplast, and bacterial lipoproteins function of lipoprotein particles is to transport water-insoluble lipids (fats) and cholesterol around the body in the blood.

65. Classification of Lipoproteins

67. Atherosclerosis

69. Summary
A knowledge of lipid biochemistry is important in understanding many current biomedical areas of interest e.g. obesity, diabetes, atherosclerosis, and the role of various polyunsaturated fatty acids in nutrition and health.

70. Content Review
What are some important functions of the essential fatty acids?
How are saturated fatty acids different from unsaturated fatty acids?
What is esterification?
What are the main functions of lipid in the body?
What are emulsifiers?