Understanding Lipids: Function, Structure & Classification

1. BCM 3000 PRINCIPLES OF BIOCHEMISTRY (Semester 1 -2011/12)

2. LIPID • Learning outcome (Objectives) • Function and distribution. • Characteristics of fatty acids-structure and chemical properties. • Saturated and unsaturated fatty acids . • Structures and properties of phospholipids, sphingolipids, waxes, terpenes and steroids.

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7. LIPID DEFINITION : General definition – all compounds called fat and oils TECHNICAL DEFINITION Fat : Triglycerides in the form of solids at room temperature Oils : Triglycerides which are liquid at room temperature

8. General Definition • Any natural compound which is insoluble or nearly insoluble in water but soluble in non-polar solvents – • Chloroform • CS2 • Ether • warm or • hot ethanol

9. FUNCTIONS Lipids are widely distributed in both animal and plant systems and perform a wide variety of functions • Structural functions - Components of membranes • Storage forms of carbon and energy • precursor for major compounds – e.g. hormones. • Insulators - thermal, electrical or physical shock • protective coatings – prevent infections, loss or addition of compounds • Regulators - as vitamins & hormones

10. CLASSIFICATION • 1. SIMPLE LIPIDS • Fatty acid esters • (Acid + alcohol  ester) • 2. COMPPOUND LIPID • Fatty acid + alcohol + OTHER COMPOUNDS

11. SIMPLE LIPIDS ??? Esters

12. COMPOUND LIPIDS 4 types of Compound lipid i.Phosphoglycerides ii. Sphingolipids iii. Cerebrosides iv. Gangliosides

13. COMPOUND LIPID

14. i & ii=Phospholipid - presence of phosphate ii , iii & iv =Sphingolipids - presence ofSphingosine iii & iv =glycolipid - presence ofcarbohydrate

15. GLYCEROL – Trihydroxy alcohol

17. FATTY ACIDS • Long chain aliphatic carboxylic acids- contains carboxyl group – polar head and `tail’ containing hydrocarbon chain • Amphiphilic compounds –hydrophilic head and hydrophobic tail • COOH can be ionised • Monocarboxyilic acids – linear hydrocarbon chain, even carbon numbers – between C12-C20 • Short, longer , branched, cyclic and odd numbers also exist BUT not many

18. Octadenic acid

19. FATTY ACIDS • 2 TYPES • Saturated Fatty acids • Unsaturated Fatty acids

20. Structure of Fatty Acids - Saturated • Fats • mostly from animal sources, • have all single bonds between the carbons in their fatty acid tails, thus all the carbons are also bonded to the maximum number of hydrogens possible. • saturated fats • The hydrocarbon chains in these fatty acids are, thus, fairly straight and can pack closely together, making these fatssolidat room temperature.

21. Saturated fatty acid –e.g. • palmitic acid (CH3(CH2)14COOH) (16C) & • Stearic acid (CH3(CH2)16COOH)

22. Saturated Fatty Acids

23. Structure of Fatty Acids - Unsaturated • Unsaturation normally at - C18 & C20 – double bond separated by methylene group -CH = CH - CH2 - CH = CH • Double bonds = cis configuration • Unsaturated fatty acid - oleic (18:1), Linoleic (18:2), Linolenic (18:3) & arachidonic (18:4)

24. Unsaturated fatty acids • C=C double bond arranged in two ways • In cis bonds, the two pieces of the carbon chain on either side of the double bond are either both “up” or both “down,” such that both are on the same side of the molecule • In trans bonds, the two pieces of the molecule are on opposite sides of the double bond, that is, one “up” and one “down” across from each other • Naturally-occurring unsaturated vegetable oils have almost all cis bonds, but using oil for frying causes some of the cis bonds to convert to trans bonds

25. CIS TRANS

27. Unsaturated Fatty Acids

28. fatty acids with trans bonds are carcinogenic, or cancer-causing. • containing products such as margarine are quite high,

29. Oils • mostly from plant sources, • have some double bonds between some of the carbons in the hydrocarbon tail, causing bends or “kinks” in the shape of the molecules. • Because some of the carbons share double bonds, they’re not bonded to as many hydrogens • oils are called unsaturated fats. • kinks unsaturated fats can’t pack as closely together, making them liquidat room temperature

30. TRANS CIS

32. Making margarine • Vegetable oils often contain high proportions of polyunsaturated and mono-unsaturated fats (oils)  liquids at room temperature. • You can "harden" (raise the melting point of) the oil by hydrogenating it in the presence of a nickel catalyst.

35. SIMPLE LIPIDS • 2 GROUPS • Neutral acyglycerols (e.g. Triacylglycerol) • Waxes • Acyglycerols • = glyceride = atryhydroxy alcohol ester • = glycerol + fatty acid (3 different fatty acids) • = can be esterified

36. Glycerol= trihydroxy alcohol

37. TRIACYGLYCEROLS

42. Triacylglycerol – the most abundant • No ionic groups -  neutral lipids • Triacylglycerol = neutral fats (solids) @ neutral oils (liquid)

43. FUNCTIONS IN ANIMALS • Adipose tissues - `fat depots' = storage forms of carbon and energy • II. Transport - chylomicrons - = lipoprotein – fatty acids are transported through lymphatic system and blood  tissue adipose tissues and other organs • III. `Physical protection' - e.g. temperature.

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47. WAXES • Also an ester - alcohol & fatty acid = very long hydrocarbon chain – commercial application • hairs, skin, leaves, fruits

48. WAXES Asid Oleic

49. CHEMICAL CHARACTERISTICS OF TRYACYLGLYCEROL (Reactions of Triacylglycerol) 1. Hydrogenation

50. Double bonds in vegetable oils can be hydrogenated  oils become solids – can control - e.g.. peanut butter - crunchy, creamy HYDROGENATION PROCESS