Lipid Chemistry. Presented By. Ayman Elsamanoudy Salwa Abo El-khair

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2 Lipid Chemistry Presented By Ayman Elsamanoudy Salwa Abo El-khair 1

3 Objectives: 1. By the end of this chapter the student should be able to: define lipids. describe the biological importance of lipids. point out basic lipid chemistry. classify lipids. explain the chemistry and main function of simple, compound and derived lipids. 2. By the end of this chapter the student should be able to apply biochemical knowledge on analyzing biochemical bases of the diseases through case study. 3

4 Introduction Lipids are heterogeneous compounds related to fatty acids. They are insoluble in water They are soluble in nonpolar solvents such as >>>> ether, acetone and chloroform. They are hydrophobic: due to predominance of hydrocarbon chain ( CH 2 CH 2 CH 2 --) in their structure

5 Biological importance of lipids: 1- Lipids act as a source of energy: they yield twice the energy produced by the same weight of carbohydrates or proteins. 2- Lipids in adipose tissue serve as energy store. 3- They contain essential fatty acids. 4- They are the natural solvent for fat-soluble vitamins.

6 Biological importance of lipids 5- Lipids have a role in protection and fixation of internal organs as kidneys. 6- Lipids in myelin sheath of nerve fibers serve as electrical insulator. 7- Lipids under the skin serve as thermal insulator.

7 Biological importance of lipids 8. Lipoproteins : - Share in the structure of cell membrane and mitochondria. -They are important for lipid transport in the blood. 9. Acetyl CoA: derived from fatty acids oxidation is used for biosynthesis of many important compound e.g. steroids.

8 Lipids Chemistry Classification of Lipids Simple lipids Compound Lipids Derived Lipids

9 Classification of lipids Simple lipids Compound lipids Derived lipids -They are formed of fatty acids and alcohol 1- Fats and Oils 2- Waxes -They are formed of : -Lipid component + -Non-lipid component 1- Phospholipids. 2- Glycolipids. 3- Sulpholipids. 4. lipoproteins -These are substances derived from simple lipids and compound lipids by hydrolysis. Also, include substance related to lipids 1- Fatty acids. 2- glycerol. 3- Steroid. 4- Isoprenoids. 5- Eicosanoids

10 Simple Lipids

11 Simple Lipids Simple lipids are esters of fatty acids with different types of alcohols. The alcohol may be glycerol (trihydric alcohol) OR other long alcohol. R1 COOH + R1 OH Fatty acid + Alcohol Simple lipids are classified into: RCOOR1 + H2O fats, oils and waxes, Ester + Water according to the type of alcohol they contain.

12 Simple Lipids 1-Fats and oils(neutral fats) They are esters of : fatty acids with glycerol. They are similar chemically, but they differ in physical properties: as oils are liquid while fats are solid at room temperature. They are called triglycerides because they are triesters formed of glycerol and 3 fatty acids.

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14 Simple Lipids Triglycerides (TG) may be : a- Simple TG: The fatty acids are the same e.g. palmitic or stearic acids forming>>>> tripalmitate or tristearate respectively. b- Mixed TG: Triglycerides with 3 different fatty acids.

15 CH 2 OH 3R COOH + CH OH CH 2 OH H2O O CH 2 O C R O CH 2 O C R O Simple TAG 3 fatty acids glycerol CH 2 O C R O CH 2 O C R1 O CH 2 O C R2 O Mixed TAG CH 2 O C R 3 Triglycerides Triglycerides with 3 different fatty acids

16 Triacylglycerol (TG) Triacylglycerols are composed of three fatty acids each in ester linkage with a single glycerol.

17 Simple Lipids 2- Waxes They are esters of fatty acids + Long chain Monohydric alcohol. They are solid at room temperature. The most important waxes in human body are cholesterol esters, which are present in blood and other tissues.

18 Fats and oils Waxes Consistency at room temperature Fats are solid Oils are liquid Solid Structure Glycerol and 3 fatty acids Long chain alcohol & fatty acid Glycerol Present Absent Long chain alcohol Absent Present Acrolein test Positive Negative Rancidity undergo rancidity Not undergo rancidity Digestion 18 Utilization by human digested by lipase Can be utilized Not Digested by lipase Can not be utilized

19 Activity 1-Give the hydrolytic product of : - Tripalmitin. - Cholesterol wax. 2-Compare between neutral fat and waxes. 19

20 Choose the best correct answer : Lipids are formed mainly of alcohol and fatty acids combined together by: a) ether link. b) peptide bond. c) glycosidic bond. d) ester bond. 20

21 Waxes : a) are liquid at room temperature. b) have positive acrolin test. c) ester of long chain alcohol with a single fatty acid d) can be digested by human 21

22 Ayman Elsamanoudy Salwa Abo El-khair

24 Glycerol Chemistry : trihydric alcohol 24

25 Physical properties: 1- It is colourless 2- viscid fluid 3- with sweet taste. 4- It is miscible with water in all proportions.

26 Chemical properties 1- Can combine with one or more fatty acids by ester bonds forming >>>> mono, di or triacylglycerol. 26

27 2- Acrolin Test: With strong dehydrating agents, as concentrated sulphuric acid, glycerol can be converted to >>>> acrolein that has very irritating pungent odour.

28 Importance of glycerol It is used in pharmaceutical and cosmetic preparations. It is used as explosive in the form of trinitroglycerine. It is used in medicine as a vasodilator agent in coronary heart diseases in the form of nitroglycerine.

29 Fatty acids These are monocarboxylic organic acids, which usually contain an even number of carbon atoms. The general formula of fatty acid is R-COOH CH3 CH2 CH2 CH2 CH2 COOH They are further classified into: Saturated & Unsaturated fatty acids according to absence or presence of double bonds.

30 Fatty acids

31 Fatty acids The carbon chain of fatty acids are numbered as: 1- starting from carboxylic group: there are two systems: a- the carboxylic group is number 1 and proceed toward the CH3 b- by using the α C adjacent to COOH and continue β, γ, δ, ε, etc.

32 Fatty acids CH3 CH2 CH2 CH2 CH2 COOH ε δ γ β α

33 Fatty acids 2- starting from the terminal CH3 group or omega carbon: ώ1 ώ2 ώ3 ώ4 ώ5 ώ6 CH3 CH2 CH2 CH2 CH2 COOH

34 Fatty acids CH3 CH2 CH2 CH2 CH2 COOH ε δ γ β α ώ1 ώ2 ώ3 ώ4 ώ5 ώ6

35 Fatty acids A. Saturated fatty acids They have no double bonds. They have the general formula : CH3 (CH2)n COOH. They are further classified, according to the number of carbon atoms, into: Short chain & Long chain fatty acids.

36 Number of carbon atoms Short chain FA Less than 10 carbons ( 2C to 10C ) Long chain FA More than 10 carbons Consistency at room temperature Liquid Solid Volatility Solubility in water Volatile Soluble Nonvolatile Insoluble Examples 36 Acetic (2 C) Butyric (4 C) Palmetic (16 C) Stearic (18 C)

37 16:0 palmitic acid A fatty acid is composed of a long hydrocarbon chain ( tail ) and a terminal carboxyl group (or head ).

38 The following table shows the formula of the most common saturated fatty acids. Short chain FA Common name Acetic acid (2C) Butyric acid (4C) Formula CH 3 COOH CH 3 (CH 2 ) 2 COOH Caproic acid (6C) CH 3 (CH 2 ) 4 COOH Long chain FA Palmitic acid (16C) Stearic acid (18C) CH 3 (CH 2 ) 14 COOH CH 3 (CH 2 ) 16 COOH Arachidic acid (20C) CH 3 (CH 2 ) 18 COOH Lignoceric acid (24C) CH 3 (CH 2 ) 22 COOH

39 B- Unsaturated fatty acids They have one or more double bonds. Most of the double bonds are of cis type. cis isomer trans isomer In case of >2 double bonds, each 2 double bonds are separated by methylene (CH2) group. -CH=CH-CH2-CH=CH-CH2-

40 For example: Oleic acid (cis form) Eliadic acid (trans form)

41 Fatty acids B- Unsaturated fatty acids They have one or more double bonds. I. Mono-unsaturated (monoethenoid) fatty acids: Contains one double bond Their general formula is CH3 (CH2)n CH = CH (CH2)x COOH

42 Fatty acids B- Unsaturated fatty acids I. Mono-unsaturated (monoethenoid) fatty acids: contains one double bond e.g.: Palmitoleic acid :(16:1Δ 9,ω 7 ) CH3 (CH2)5 CH = CH (CH2)7 COOH n = 5 x = 7 Contain 16 C, one double bond Double bond between C9 and C10 from COOH ώ7 means: double bond between C7 and C8 from terminal CH3 ( ώ1 )

43 Fatty acids B- Unsaturated fatty acids I. Mono-unsaturated (monoethenoid) fatty acids: contains one double bond e.g.: Palmitoleic acid :(16:1Δ 9,ω 7 ) CH3 (CH2)5 CH = CH (CH2)7 COOH Oleic acid : (18:1Δ 9,ω 9 ) CH3 (CH2)7 CH = CH (CH2)7 COOH Nervonic acid :(24:1Δ 15,ω 9 ) CH3 (CH2)7 CH = CH (CH2)13 COOH

44 II. Polyunsaturated (polyethenoid) fatty acids: Contains more than one double bond. Linoleic acid : (18C:2 Δ 9,12, ω 6 ) CH3 (CH2)4 CH = CH CH2 CH = CH (CH2)7 COOH Linolenic acid : (18C:3 Δ 9,12,15, ω 3 ) CH3 CH2 CH=CH CH2 CH=CH CH2 CH=CH (CH2)7 COOH

45 Arachidonic acid : (20C: 4 Δ 5,8,11,14, ω 6 ) CH3 (CH2)4 CH=CH CH2 CH=CH CH2 CH=CH CH2CH=CH (CH2)3 COOH

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47 The packing of fatty acids into stable aggregates

48 Def: Essential fatty acids They are polyunsaturated fatty acids i.e. fatty acids, which contain more than one double bond. They must be taken in diet because the body cannot synthesize them, as the enzymes that are needed for their synthesis are absent in humans. Examples : Linoleic (18C+ 2double bonds), Linolenic (18C+ 3double bonds) and Arachidonic acids (20C+ 4double bonds).

49 Importance of Essential Fatty Acids 1. They are essential for growth. 2. They are essential for phospholipids formation. 3. Arachidonic acid, which is one of the essential fatty acids, is important for biosynthesis of prostaglandins. 4. They form cholesterol esters (less liable to be deposited in blood vessels)>>>> So, protect against Atheroscelerosis.

50 Saturated FA Short chain Saturated FA Long chain Fatty Acids Monounsaturated Polyunsaturated Acetic acid (2C) Palmitic acid (16C) Palmitoleic acid (16:1Δ9,ω7) Linoleic acid : (18C:2 Δ9,12, ω6) Butyric acid (4C) Stearic acid (18C) Oleic acid : (18:1Δ9,ω9) Linolenic acid (18C:3 Δ9,12,15, ω3) Caproic acid (6C) Arachidic acid (20C) Nervonic acid (24:1Δ15,ω9) Arachidonic acid (20C: 4 Δ5,8,11,14, ω6) Lignoceric acid (24C)

53 General properties of fatty acids They usually contain an even number of carbon atoms. They have straight chains. They may be saturated or unsaturated. Unsaturated fatty acids are more reactive than saturated fatty acids. Some fatty acids are hydroxylated eg. cerebronic acid. Lower FAs are soluble in water & this solubility decreases with increasing chain length. Palmitic, stearic and oleic acids make up the bulk of animal depot fat.

54 Physical properties of fatty acids 1. They are colourless, odourless and tasteless. 2. Solubility in water: Short chain fatty acids are soluble in water. The solubility decreases with the increase in chain length. Long chain fatty acids are insoluble in water but solublein nonpolar solvents.

55 3. Melting point: It depends on: - The length of the chain of fatty acid - The degree of unsaturation. Short chain and unsaturated fatty acids: - They have lower melting point. - They are liquid at room temperature. Long chain saturated fatty acids: -They have higher melting point. - They are solid at room temperature.

56 4. Optical (Geometric) stereoisomerism: Fatty acids that contain double bond can be present in cis (mostly) and trans stereoisomeric forms. Cis configuration means that the groups around the double bond are on the same side of the bond. Trans configuration means that the groups around the double bond are on the opposite sides of the bond.

57 4. Optical (Geometric) stereoisomerism: Fatty acids that contain double bond: cis (mostly) and trans forms. For example: oleic acid, which is a cis form, and its isomer eliadic acid, which is a trans form.

60 Def: Rancidity Rancidity is a condition in which fat attains a bad taste and disagreeable odour. Types of rancidity There are 2 types of rancidity: Hydrolytic rancidity Oxidative rancidity

61 There are 2 types of rancidity: Hydrolytic rancidity Fats are hydrolyzed into glycerol and fatty acids in presence of : - Moisture. - Warm temperature - Bacterial enzymes Oxidative rancidity It occurs by oxidation of unsaturated fatty acids present in fats and oils forming lipid peroxides, fatty aldehydes, ketones and short chain fatty acids.

62 Predisposing factors of rancidity Rancidity is predisposed by: Light. Moisture. Warm temperature. Effects of rancidity Rancidity leads to: Fats and oilsattain bad taste. Fats and oilsattain disagreeable odour. Production of toxic compounds as lipid peroxidies, aldehydes and ketones.

63 Prevention of rancidity: Avoid exposure of fats to light, moisture and high temperature. Addition of antioxidants to fats and oils specially the natural antioxidant tochopherol (vitamin E).

64 Activity 1- Differentiate between short and long chain FA. 2- Differentiate between saturated and unsaturated FA. 3- Essential FA (def. examples and importance). 4- What is acrolin test,mention its biochemical use. 5- Mention three uses of glycerol. 6- Rancidity (types, effects and prevention) 64

65 Choose the correct answer: Example of saturated FA: a) arachidonic acid b) Oleic acid c) palmitic acid d) Linoleic acid 65

66 The following are essential fatty acids except: a) palmitoleic acid b) arachidonic c) linolenic d) Linoleic acid 66

67 Regarding Eliadic acid (18C:1Δ 9,ω 9 ), all are true EXCEPT a) It is non-essential FA b) It is the trans isomer form of linoleic acid c) It is 18 C d) It is monounsaturated FA 67

68 Rancidity is a process of oxidation concerning : a) short chain FA b) saturated FA. c) hydroxy FA d) unsaturated FA 68

69 Concerning Linoleic acid (18C:2Δ 9,12,ω 6 ),what is not true: a) it is unsaturated FA b) It contains 2 double bonds c) The last double is 6 carbon atom from its last C. d) The first double bond lies between C8-C9. 69

70 Rancidity can be prevented by addition of : a) vitamin B b) vitamin D c) Vitamin E d) vitamin K 70