Lipids

Lipids are soluble in nonpolar organic compounds

They have a variety of structures and functions

Fatty Acids Are Carboxylic Acid with Hydrocarbon Chains

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

Polyunsaturated fatty acids have more than one double bond

Triacylglycerols

The three OH groups of glycerol are esterified with fatty acids

CH2 OH

CH OH

CH2 OH

R1 C OH

O

R2 C OH

O

R3 C OH

O

CH2 O

CH O

CH2 O

C

C

C

O

O

O

R1

R2

R3

glycerol fatty acidsa triacylglycerola fat or an oil

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 1-2 7-11 3-4 83-89

Soybean 1-2 6-10 2-4 84-91

Marine Oils Whale 5-10 10-20 2-5 65-83

Fish 6-8 10-25 1-3 64-83

C14 = myristic acid Unsaturated: Oleic (1)

C16 = palmitic acid Linoleic (2)

C18 = stearic acid Linolenic (3)

Phosphoacylglycerols

The terminal OH group of glycerol is esterified with phosphoric acid

They are the major components of cell membranes

The most common phosphoacylglycerols in membranes have a second phosphate ester linkage

Phosphoacylglycerols are classified as phospholipids

Phosphoacylglycerols form membranes by arrangingthemselves 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 the major lipid components in the myelin sheaths of nerve fiber

They are also found in membranes

Two of the Most Common Kinds of Sphingolipids

Prostaglandins are synthesized from arachidonic acid

They are responsible for regulating a variety of physiological responses

Prostaglandins

COOHH

H

postaglandin skeleton

Name in the format PGX, with X designating the functional groups of the five-membered ring

COOHH

H

O

HO OH

H

H

O

HO OH

COOH

H

HHO OH

COOH

HO

PGE1PGE2

PGF2

Naming Prostaglandins

Terpenes contain carbon atoms in multiples of five

They are made by joining together 5-carbon isoprene units

Terpenes

Oxygen-containing terpenes are sometimes called terpenoids

The Isoprene Rule

Squalene, a triterpene, is a precursor of steroid molecules

Lycopene and -carotene are tetraterpenes calledcarotenoids

Formation of geranyl pyrophosphate

Terpene Biosynthesis

Hormones are chemical messengers

Many hormones are steroids

All steroids contain a tetracyclic ring system

Steroids

Methyl groups at C-10 and C-13 are called angular methyl groups

The B, C, and D rings are trans fused

Thoseon the opposite side of the plane of the ring system are -substituents

Substituents on the same side of the steroid ring systemas the angular methyl groups are -substituents

The A and B rings are also trans fused in most naturallyoccurring steroids

Classification of Steroids

1. Sterols2. Bile Acids3. Hormones

Adrenocorticoid hormon Sex hormones

4. Steroid Glycosides

5. Steroid Alkaloids

6. Miscellaneous Steroids Toxines… etc…

Cholesterol Is a Steroid

bile acids (C24) CHOLESTEROL vitamin D (C27) h

pregnenolone (C21)

progesterone (C21)

glucocorticoids (C21) sex hormones mineralocorticoids (C21)

androgens (C19)

estrogens (C18)