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Medical Biochemistry (2) Level 2 Part V (Lipids)

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1 Medical Biochemistry (2) Level 2 Part V (Lipids)
Taif University College of Medicine Preparatory Year Students Medical Biochemistry (2) Level 2 Part V (Lipids)

2 Lipids

3 Lectures outlines Definition and importance of lipids
Classification of lipids Fatty acids structure and properties Important reactions of FA Glycerides Non-glyceride lipids Membranes Lipids

4 What are lipids?

5 Definition A collection of organic molecules of varying chemical composition. They are grouped together on the basis of their solubility in nonpolar solvents (ether, chloroform, benzene, acetone) but insoluble in water. Lipids include fats, oils, waxes and related compounds. They are widely distributed in nature both in plants and in animals.

6 The great structural diversity among lipids
The defining parameter for lipids is solubility rather than structure.

7 What are the Biological Functions of Lipids?

8 The biological functions of lipids
Energy source (Fatty acids) Energy storage (triacylglycerols) Structural components of cell membrane (phospholipids, sphingoglycolipids, and cholesterol) Hormones (steroid hormones) Emulsifiers (Bile salts) Protection and insulation (biological waxes) Source of Fat-soluble Vitamins Vitamins absorption


10 What are the Classes of Lipids?


12 Lipids Classification

13 What is the general structure of fatty acids?

14 Nonpolar Hydrophobic Tail
Fatty Acids Usual fatty acids are unbranched Aliphatic carboxylic acids Nonpolar Hydrophobic Tail polar Hydrophilic Head Saturated Unsaturated R without double bonds have carbon-carbon double bonds

15 Fatty Acids Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from triglycerides or phospholipids. When they are not attached to other molecules, they are known as "free" fatty acids. Fatty acids are important sources of fuel because they yield large quantities of ATP. Many cell types can use either glucose or fatty acids for this purpose. In particular, heart and skeletal muscle prefer fatty acids.

16 Length of free fatty acid chains
Fatty acid chains differ by length, often categorized as short to very long. aliphatic tails < 6 carbons Short-chain fatty acids (SCFA) aliphatic tails carbons Medium-chain fatty acids (MCFA) aliphatic tails carbons Long-chain fatty acids (LCFA) aliphatic tails > 23 carbons Very long chain fatty acids (VLCFA)

17 Fatty Acids Common fatty acids

18 Fatty Acids Fatty acids

19 Unsaturated fatty acids
Common Fatty Acids

20 Dealt () Omega () 18:2 9,12 18:2 6,9 Linoleic acid 18:2
Fatty Acids Dealt () Omega () Numbering -COOH -CH3 -COOH -CH3 9 12 9 6 18:2 9,12 18:2 6,9 Linoleic acid 18:2

21 Omega-3 & Omega-6 fatty acids

22 Systematic nomenclature
Stearic acid are non-systematic historical names, which are the most frequent naming system used in literature Trivial nomenclature (or common names) octadecanoic acid derive from the standard IUPAC Rules for the Nomenclature of Organic Chemistry Systematic nomenclature (IUPAC names) 18:2 9,12 the location of the double, counting from the carboxylic acid end. Δx nomenclature (or delta-x) 18:2 6,9 the location of the double, counting from the terminal methyl carbon ωx nomenclature (or omega –x) Lipid numbers take the form C:D where: C = the number of carbon atoms and D = the number of double bonds in the fatty acid

23 Summary of the ways for designating fatty acids

24 Lecture notes (Dr Gaber Shehab)
Essential fatty acids Fatty acids that are required by the human body but cannot be made in sufficient quantity from other substrates, and therefore must be obtained from food. There are two essential fatty acids: linoleic acid and linolenic acid. These two acids: (1) are needed for proper membrane structure and (2) serve as starting materials for the production of several nutritionally important longer-chain omega-6 and omega-3 acids Linoleic acid (18:2) is the primary member of the omega-6 acid family, and linolenic acid (18:3) is the primary member of the omega-3 acid family. Biochemistry Department

25 Questions What are the differences between saturated and unsaturated fatty acids? Write the chemical structure, the IUPAC name, the delta and the omega number of the following fatty acids: Palmitic Stearic Palmitoleic Oleic Linoleic Linolenic

26 IUPA name and structure of common fatty acids

27 Important reactions of FA
Esterification Hydrolysis of esters Hydrogenation Effect of radiation

28 Esterification

29 Esterification Fatty acids + Alcohol H +/ Heat Ester + Water

30 Hydrolysis of esters Acid hydrolysis Base hydrolysis (Saponification)

31 Acid Hydrolysis Ester H +/ Heat Acid + Alcohol

32 Base Hydrolysis Ester Saponification OH - Salt of the acid + Alcohol

33 Hydrogenation

34 Hydrogenation Oleic acid Stearic acid

35 Lecture notes (Dr Gaber Shehab)
Effect of radiation Splitting the Bay bond- Free rotation – Reforming the bond Changing the configuration of the double bond Biochemistry Department

36 Lecture notes (Dr Gaber Shehab)
Effect of radiation Splitting the C-C bond- Biochemistry Department

37 Classification Scheme for Fatty acids

38 Glycerides

39 Lipids Classification

40 Neutral- glycerides Phospho- Glycerides

41 Neutral -glycerides

42 Esters of Fatty acids with Glycerol
Glycerides Neutral glycerides Esters of Fatty acids with Glycerol

43 Esterification HO 3 H2O Ester Bond Triglyceride

44 Structure of the simple triacylglycerol
The simple triacylglycerol produced from the triple esterification reaction between glycerol and three molecules of stearic acid (18:0 acid). Three molecules of water are a by-product of this reaction.

45 Structure of a mixed triacylglycerol
Three different fatty acid residues are present

46 Triglycerides Monoacid Mixed Di-acid Tri-acid Triglycerides Tristearin
Palmito, Oleo, Stearin Stearo, Stearo, Palmitin

47 Question Draw the structural formula of the triacylglycerol produced from the reaction between glycerol and three molecules of oleic acid?

48 Hydrolysis of Triglycerides
Glycerol Enzymatic or Acid Hydrolysis Lipase Alkaline Hydrolysis Glycerol Saponification

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