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

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Presentation on theme: "Prof. Dr. Suat Erdoğan EBN School of Medicine Medical Biochemistry Department October 2013."— Presentation transcript:


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

3 Outline Description of lipids Function of lipids Fatty acids Triglycerides Cholesterol Steroids

4 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.

5 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

6 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)

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

8 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.

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

10 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.


12 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.

13 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.

14 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.

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

16 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.

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

18 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: a. Monoansaturated acids, containing one double bond (oleic acid). b. Polyunsaturated acids containing two or more double bonds (linoleic acid, arachidonic acid).




22 Saturated fatty acid structure omega endalpha end degree of saturation 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 Stearic acid: C18H38O2


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


26 Unsaturated fatty acids Palmitoleic acid (16:1) Oleic acid (18:1) Linoleic acid (18:2) -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.

27 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.


29 Monounsaturated Fatty Acid Structure omega endalpha end One double bond 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

30 Polyunsaturated Fatty Acid Structure omega endalpha end > 2 double bonds 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

31 Essential Fatty Acid- Omega-6 (linoleic acid) omega endalpha end 1st double bond is located on the 6th carbon from the omega end 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

32 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

33 Essential Fatty Acid- Omega-3 (linolenic acid) omega endalpha end 1st double bond is located on the 3rd carbon from the omega end 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

34 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.

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

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

37 Fats

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

39 Triglyceride synthesis (Ester bond) Glycerol + 3 FAs Triglyceride + 3 H 2 0 H H--C--OH H--C--OH H--C--OH H O HO-C-R O HO-C-R O HO-C-R + H O H--C--O--C-- O H--C--O--C-- O H--C--O--C-- H R + H 2 O R + H 2 0

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

41 Trans and cis fatty acids





46 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

47 Structure of phospholipids

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

49 Emulsifier Hydrophilic end (attracts water) Hydrophobic end (attracts lipid)

50 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.

51 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.

52 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

53 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


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

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

57 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

58 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.


60 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.)thromboxanesprostacyclins

61 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

62 Prostaglandins Research on the involvement of PGs in reproductive physiology has produced several clinically useful derivatives 15-Methyl-PGF 2 is used as a therapeutic abortifacient

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

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

65 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.

66 Classification of Lipoproteins


68 Atherosclerosis


70 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.

71 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?

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