CH 8: Lipids

Lipids Defined A lipid is an organic compound found in living organisms that is: insoluble (or only sparingly soluble) in water soluble in non-polar organic solvents. Lipids do not have common functional groups that serves as the basis for defining such compounds.

Functions of Lipids Source of energy – 9kcal/gram Provide thermal insulation and pad organs Component of all cells – in membranes Some act as hormones – steroid hormones Protective coating - waxes

Types of Lipids Energy-storage lipids –triacylglycerols, triglycerols, “fats” Membrane lipids - phospholipids, sphingo(glyco)lipids, and cholesterol Emulsification lipids - bile acids Chemical messenger lipids - steroid hormones and eicosanoids Protective-coating lipids - biological waxes

Fatty Acids (FA) Fatty acids are naturally occurring unbranched monocarboxylic acids Biological FA have an even # of carbon atoms: Short-chain fatty acids: C4 - C5-6 Medium chain fatty acids: C6-8 - C10 Long chain fatty acids: C12 - C26

Types of Fatty Acids Saturated (SFA) Unsaturated Fatty Acids Fatty acid with only C to C single bonds Unsaturated Fatty Acids Monounsaturated (MUFA) - FA with one C to C double bond present Polyunsaturated (PUFA) - FA with 2 or more C to C double bonds present Double bonds are in the cis form

Fatty Acids

Mono-unsaturated Fatty Acids w D

Describing Fatty Acids Identify omega & delta “end” of the fatty acid State number of carbons: # double bonds Give location of double bonds, counting from the delta “end”

Properties Fatty Acids Water solubility decreases as C# increases Short chain FA are fairly water soluble Medium and long chain FA are water insoluble As the number of carbons increases so does the melting point For a given number of carbons, mp increases as the # of cis double bonds increases Trans double bonds do not impact mp significantly UC Davis Wiki

Triglyceride = glycerol + 3 fatty acids aka - triglycerols

TG Formation – 3 ester linkages Triglyceride

Properties of TG The nature of the fatty acids bonded to the glycerol backbone determines the properties of the TG Fats – solid TG Primarily saturated fatty acids Primarily animal sources Oils – liquid TG Many unsaturated fatty acids Good sources - plant and fish oils

Sources of FA Saturated FA MUFA PUFA Animals fats Butter, lard, lamb, beef…. Coconut “oil” MUFA Olive oil Canola oil PUFA Vegetable oils, corn oil,

Reactions of TG Hydrolysis Saponification – 2 step process + 3 H2O  glycerol + 3 FA (or a monoglyceride and 2 FA) Reaction requires heat and acidic conditions OR digestive enzymes Saponification – 2 step process Step one, hydrolyze the TG to 3 FA + glycerol Step two, react the FA with 3 NaOH or 3 KOH  3 soaps

3. Hydrogenation reaction -- add H2 to the double bonds -- complete hydrogenation converts all double bonds to single bonds (fully hydrogenated) --reaction saturates the oil --partial hydrogenation occurs when some of the double bonds are hydrogenated --remaining double bonds are often converted in to trans form

Oxidation of unsaturated FA –> rancid oil …CH=CH…. (O) 2 aldehydes (O)  2 carboxylic acids

Essential Fatty Acids Fatty acids that must be obtained from dietary sources – are not synthesized within the body Two most important essential fatty acids are: Linoleic acid (18:2) - omega 6 Linolenic acid (18:3) - omega 3 Both are needed for: Proper membrane structure Serve as starting materials for the production of several nutritionally important longer-chain omega-6 and omega-3 fatty acids

Current recommended amounts are: total fat intake in calories: 15% - Monounsaturated fat 10% - Polyunsaturated <10% - Saturated fats Studies also indicate that: Monounsaturated fats are considered “good fats” Saturated fats are considered “bad fats” Trans-monounsaturated fats are considered “bad fats” Polyunsaturated fats can be both “good fats” and “bad fats” Omega 3 and 6 are important “good fats”

Membrane Lipids Phospholipids Sphingoglycolipids Cholesterol (steroid) Glycerophospholipids Sphingophospholipids Sphingoglycolipids Cholesterol (steroid) See page 314

Phospholipids aka - glycerophospolipid

Sphingophospholipid See page 313 and 314 Sphinogosine backbone with Fatty acid bonded to sphingosine by an amide bond Phosphate bonded to an amino alcohol

Relate this structure to that on page 313 http://themedicalbiochemistrypage.org/sphingolipids.html http://lipidlibrary.aocs.org/Lipids/introsph/index.htm

Sphingoglycolipids

Cholesterol – found in the membranes of animal cells General steroid structure

Steroids – Functions Vary Membrane lipids Cholesterol – animal cell membranes Messenger lipids Hormones – testosterone, estrogen, see pages 322/23 Emulsification lipids Bile salts

Messenger Lipids - Eicosanoids Eicosanoids are Arachidonic acid (20:4) derivatives: Have profound physiological effects at extremely low concentrations. Eicosanoids are hormone-like molecules Exert their effects in the tissues where they are synthesized. Eicosanoids usually have a very short “life.” Physiological effects of eicosanoids: Inflammatory response Production of pain and fever Regulation of blood pressure Induction of blood clotting Control of reproductive functions, such as induction of labor Regulation of the sleep/wake cycle

Eicosanoids Arachidonic acid (20:4) derivatives