Lipids

Lipids are soluble in nonpolar organic compounds They have a variety of structures and functions

Fatty Acids Are Carboxylic Acid with Hydrocarbon Chains

Polyunsaturated fatty acids have more than one double bond The double bonds in naturally occurring fatty acids Have the cis configuration Double bonds in naturally occurring unsaturated Fatty acids are separated by one methylene group

The three OH groups of glycerol are esterified with fatty acids Triacylglycerols a triacylglycerol a fat or an oil glycerol fatty acids The three OH groups of glycerol are esterified with fatty acids

Fats are triacylglycerols existing as solid or semisolid state at room temperature

Oils are liquid triacylglycerols

Average composition of fatty acids % Type Fat, Oil C14 C16 C18 Unsaturated Animal Fats Butter 8-15 25-29 9-12 44-58 Lard 1-2 25-30 6-12 56-68 Beef tallow 2-5 24-34 15-30 31-59 Vegetable Oils Olive 0-1 5-15 1-4 80-94 Peanut - 7-12 2-6 82-91 Corn 7-11 3-4 83-89 Soybean 6-10 2-4 84-91 Marine Oils Whale 5-10 10-20 65-83 Fish 6-8 10-25 1-3 64-83 C14 = myristic acid Unsaturated: Oleic (D1) C16 = palmitic acid Linoleic (D2) C18 = stearic acid Linolenic (D3)

Phosphoacylglycerols They are the major components of cell membranes The terminal OH group of glycerol is esterified with phosphoric acid

The most common phosphoacylglycerols in membranes have a second phosphate ester linkage Phosphoacylglycerols are classified as phospholipids

Phosphoacylglycerols form membranes by arranging themselves into a lipid bilayer Saturated fatty acids decrease membrane fluidity because their hydrocarbon chains can pack closely together. Unsaturated fatty acids have the opposite effect

Sphingolipids They contain sphingosine instead of glycerol They are also found in membranes They are the major lipid components in the myelin sheaths of nerve fiber

Two of the Most Common Kinds of Sphingolipids

Prostaglandins Prostaglandins are synthesized from arachidonic acid They are responsible for regulating a variety of physiological responses Name in the format PGX, with X designating the functional groups of the five-membered ring postaglandin skeleton

Naming Prostaglandins PGE2 PGE1 PGF2a

Terpenes Terpenes contain carbon atoms in multiples of five They are made by joining together 5-carbon isoprene units Oxygen-containing terpenes are sometimes called terpenoids

The Isoprene Rule

Squalene, a triterpene, is a precursor of steroid molecules

Lycopene and b-carotene are tetraterpenes called carotenoids

Terpene Biosynthesis Formation of geranyl pyrophosphate

Steroids All steroids contain a tetracyclic ring system Many hormones are steroids Hormones are chemical messengers

Methyl groups at C-10 and C-13 are called angular The B, C, and D rings are trans fused Methyl groups at C-10 and C-13 are called angular methyl groups

The A and B rings are also trans fused in most naturally occurring steroids Substituents on the same side of the steroid ring system as the angular methyl groups are b-substituents Those on the opposite side of the plane of the ring system are a-substituents

Classification of Steroids 1. Sterols 2. Bile Acids 3. Hormones Adrenocorticoid hormon Sex hormones 4. Steroid Glycosides 5. Steroid Alkaloids 6. Miscellaneous Steroids Toxines… etc…

Cholesterol Is a Steroid