Lipid:
Lipids are biomolecules which are soluble in nonpolar solvents (insoluble in water.)
Simple Lipids - not hydrolyzed by aqueous base. Terpenes, steroids, and prostaglandins.
Complex Lipids - hydrolyzed by aqueous base (all are esters and/or amides). Triaylglycerols (triglycerides, fats, and oils), waxes, phosphoglycerides, sphingophospholipids, and glycosphingolipids.
Fatty Acid:
A key component in making most lipids, fatty acids are carboxylic acids typically having an even number of carbons.
“Saturated” fatty acids have no C=C. Stearic acid (below) is an 18 carbon saturated fatty acid.
OH
O
Unsaturated fatty acids have one C=C (monounsaturated) or more C=C (polyunsaturated) such as
O
OH oleic
H O and arachidonic
O
acids.
Some of the fatty acids needed to make lipid are not produced by the body and must be gotten in the diet. These “essential” fatty acids have cis double bonds at the omega 6 and the omega 3 positions. Arachidonic acid (shown above) can be produced by our bodies from linoleic acid in our diet.
OH OH
O O linoleic and linolenic acids.
Most naturally occurring unsaturated fatty acids have cis double bonds. Partial hydrogenation of fatty acids (usually in fats and oils) produces some trans fatty acids. (Example: partial hydrogenation of fat shown below.)
O O
CH
2
O
O
CH O
O
H2
CH
2
O
O
CH O
O
CH
2
O
CH
2
O
Soap: the salt of fatty acid usually made by the saponification of fat. Have a polar end and a long nonpolar chain. When mixed with water soap molecules cluster together forming spherical micelles with an nonpolar interior and a polar surface.
Detergent: structurally similar to soap but with a different functional group at the polar end (ex. salt of a sulfonic acid).
Wax:
Waxes are made by linking a saturated fatty acid and a long chain alcohol to form an ester. (Example: formation of beeswax shown below). Commonly found as a protective coating on skin, fur, feathers, fruit, etc.. Soft when warm, hard when cold.
O
OH
+
H O
O
O
+
H2O
Triglyceride (triacylglycerol, fat, oil):
Three fatty acids esterified to one glycerol. The alcohol, glycerol, is linked to 3 fatty acids to produce the triacylglycerol ester. The 3 fatty acids may have the same or different structures. Unsaturated fatty acids produce unsaturated fat.
Oils - liquid, unsaturated triglycerides from plants.
(Exceptions: Palm and coconut oils are saturated)
Fats - solid, saturated triglycerides from animals.
CH
2
OH
CH OH
CH
2
OH glycerol
O
CH
2
O
O
CH O
O
CH
2
O a polyunsaturated fat (“many” C=C)

Phospholipid: A generic term for lipids containing phosphate esters including both phosphoglycerides and sphingomyelins
(discussed below). Are an important part of cell membrane (lipid bilayer).
Phosphoglyceride (glycerophospholipid):
Made from a glycerol, 2 fatty acids, a phosphate, and an aminoalcohol.
A major category of phospholipid which is much like a fat with one fatty acid replaced by a phosphate forming a phosphate ester. The phosphate is also esterified to a small alcohol (i.e. ethanolamine, choline). Found primarily in cell membranes.
CH
2
O
O
O
H O
+
NH
3 ethanolamine
H O choline
N
+
Sphingomyelin (phosphosphingolipid):
A category of phospholipid most commonly found in brain and nerve tissue.. Made from a sphingosine, a fatty acid, a phosphate and an
CH
CH
2
O
O
O P
O
O
+
NH
3 phosphoglyceride aminoalcohol. Notice the similarities between the 3 carbons at one end of sphingosine and the 3 carbons in glycerol Like phosphoglycerides, sphingophospholipids have a fatty acid connected at the 2nd carbon from the end (except as an amide not an ester) and a second alcohol esterified to the phosphate attached to the end carbon.
CH OH
O
CH
CH
OH
NH
2
CH
2
OH
CH N
H
O
CH
2
O P
O
O
+
NH
3
CH OH
CH
2
OH
CH
2
OH
sphingosine glycerol sphingophospholipid
In fact if one bond in the sphingophospholipid is rotated, it is possible to see that both molecules have two nonpolar
(hydrophobic) chains attached to a polar (hydrophilic) region containing many heteroatoms.
O nonpolar nonpolar
CH
2
O
O
H O CH
O
CH O
O
CH
2
O P
O
O
+
NH
3
CH N
H
O
CH
2
O P
O
O
+
NH
3
Terpenoid (terpene):
Made from isoprene these molecules have branched chains or rings containing a multiple of 5 carbons often with heteroatoms attached.
Steroid:
Made from the terpene squalene, these molecules have the a four ring core structure shown below. This category includes cholesterol, cortisone, testosterone (an androgen), and estradiol (an estrogen).
O
OH
OH
O estragen (estradiol) prostaglandin core structure steroid four ring core
H O
H O
OH prostaglandin E2 (PGE2)
Prostaglandin:
Made from arachidonic acid, these compounds have a core structure with a five membered ring and two adjacent chains, shown above. These lipids function as hormones and system regulators.