Learn Your Lipids. Why are lipids insoluble in water but soluble in nonpolar solvents?

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1 Learn Your Lipids What are lipids? Lipids are organic molecules of biological origin that are insoluble in water and soluble in nonpolar solvents Why are lipids insoluble in water but soluble in nonpolar solvents? Lipids have large nonpolar regions, consequently o Lipids do not dissolve in water which is polar o Lipids dissolve in nonpolar solvents like dissolves like Example: the solubility of Arachidic acid is controlled by the nonpolar region outlined above Vocabulary: Nonpolar Hydrophobic: water hating Lipophilic: fat loving Polar Hydrophilic: water loving Lipophobic: fat hating Where are lipids found? Lipids are found in fatty acids, membranes, and other nonpolar biological tissues How many different kinds of lipids are there? There are 8 general categories of lipids: fatty acids, waxes, triacylglycerides, phospholipids, prostaglandins, steroids, lipophilic vitamins, and terpenes o Terpenes are not discussed in Chemistry 14C Fatty Acids:

2 Structure: o Fatty acids are composed of a carboxylic acid with a long unbranched hydrocarbon chain Biological function: o Precursor to other lipids Most fatty acids have an even number of carbons o Usually between o Most biologically important fatty acids have 18 carbons There are 2 categories: saturated and unsaturated o Saturated fatty acids have no C=C bonds o Unsaturated fatty acids have one or more C=C bonds Monounsaturated: contains one C=C bond Polyunsaturated: contains more than one C=C bond Examples: Stearic acid: 18 carbons & saturated Oleic acid: 18 carbons & unsaturated (monounsaturated) Linolenic acid: 18 carbons & unsaturated (polyunsaturated) Notice how in the examples above, the structures have cis conformations

3 o Cis fatty acids are common because they are more readily digested by animals o Trans fatty acids are less abundant because they linger in the body and cause arterial plaque o Although cis conformations are more common, trans conformations exist Waxes: Structure: o Most natural waxes are esters derived from a fatty acid and a long chain alcohol Biological function: o Water barriers Generic Structure: Triacylglycerol (triacylglyceride):

4 Structure: o Fatty acid triester of glycerol (glycerin) Biological function: o Energy storage Fat if solid at room temperature & oil if liquid at room temperature Most abundant of lipids Yield soaps upon hydrolysis Generic structure: How does soap work? 1) The polar CO 2 groups are attracted to water 2) Nonpolar hydrocarbon chains avoid water 3) Nonpolar hydrocarbons are attracted to the nonpolar dirt Pink circle= nonpolar hydrocarbons Blue Phospholipids: box= polar CO 2 Structure: 4) Micelles are formed which suspend the dirt in water 5) The micelles carry away the dirt when the water is removed

5 o glycerol esterified with 2 fatty acids and 1 phosphate group biological function: o cell membranes (phospholipid bilayer) Second most abundant of natural lipids Hydrophobic effect: hydrophobic tails avoid water o similar to micelles Example: phosphatidic acid: phospholipid with the phosphate group bonded only to glycerol Phospholipid bilayer Prostaglandin:

6 Structure: o Molecule having prostanoic acid skeleton Biological function: o regulators and signal molecules Cause constriction and dilation in smooth muscles Regulate aggregation and disaggregation of platelets Sensate spinal neurons to pain Regulate inflammatory mediation, calcium movement, and hormones Control cell growth Generic structure: Steroids: Structure: o A molecule having a nonlinear ring system Biological function: o Steroids have similar structure but a wide range of functions o Sex hormones: give rise to sexual characteristics o Corticoid hormones: regulate metabolic processes Cortisone: glucocorticoid hormone that regulates inflammation and glucose metabolism Aldosterone: mineralocorticoid hormone that regulates Na+/K+ balance o Bile acids: Cholic acids: aid in digestions by emulsifying fats in the intestine Nearly planar structure Generic Structure:

7 Example: o Cholesterol (the biological precursor to all other vertebrate steroids) Lipophilic vitamins: Vitamin: organic compound, other than fat, protein, or carbohydrate, required for normal growth and maintenance of animals Not all vitamins are lipophilic vitamins o Vitamin C is hydrophilic and thus is not a lipid Broad range of structures and functions Examples Vitamin E: protects against oxidative damage to cells from radicals

8 Vitamin A (retinol): essential to vision Quick Review: fa)y acids waxes saturated unsaturated monosaturated polysaturated triacylglycerols Lipids phopholipids prostaglandins sex hormones steriods cor8col hormones lipophillic vitamins bile acids terpenes

9 Fatty Acids Lipid Generic Structure Waxes Triacylglycerides Phospholipids R R X Prostaglandins Steroids Lipophilic Vitamins No Generic Structure

10 References Hardinger, Steven. Chemistry 14C: Organic Molecular Structures and Interactions: Lecture Supplements. Plymouth, MI: Hayden McNeil Pub., Print. Hardinger, Steven. Organic Chemistry at UCLA. N.p., n.d. Web. 9 June < All images from illustrated glossary