You will find there a simplified nomenclature
of the main groups of the simple lipids present in animal and vegetal cells, or
chemically made. Several
lipids from bacteria, algae, fungi and plants are omitted as they are not found frequently
in natural extracts. If interested, the reader should refer to specialized
books, internet, articles or general data bases.
ACYLGLYCEROLS - ALKYLGLYCEROLS
They are also named Glycerides
or neutral glycerides. They are fatty acid esters of one glycerol (trihydric alcohol)
or up to three glycerol, sometimes alkyl ethers of glycerol (ether lipids) are
found. In some acylglycerols the acyl part is not a simple fatty acid but a
phenolic or a terpenic acid.
From
these possible structures there are four sub-groups :
- Monoacylglycerols (or monoglycerides) with one fatty acid
(or one phenolic acid, or one terpenic
acid) esterified to glycerol and monoalkylglycerols
- Diacylglycerols (or diglycerides) with two fatty acids
(or phenolic or terpenic
acids) esterified to
glycerol and dialkylglycerols
- Triacylglycerols (or triglycerides) with three fatty acids
(or phenolic acids) esterifying the three alcohol groups of glycerol
and alkyldiacylglycerols
- Polyglycerol
esters with one or
two fatty acids esterifying a polyglycerol
Short-chain aldehydes are produced from fatty hydroperoxides but are also found in vegetals. Long-chain aldehydes occur in free form but are frequently included in complex lipids in the form of vinyl ether (plasmalogen analogs of glycerides or phospholipids).
AMINO COMPOUND-CONTAINING LIPIDS
Several classes of lipids have been identified containing fatty acids, normal or hydroxylated, combined with :
one amino acid in bacteria (serine, lysine, ornithine, glycine or tyrosine : lipoamino acids),
several aminoacids (lipopeptides)
carnitine in all cells,
dopamine in some brain cells.
one aminoalcohol (ethanolamine)
one molecule of urea (diacyl urea)
Group including some long carbon chain (18 to 20 or longer) with an alcohol group and a branched amine group (ex. sphingosine). Largely found in complex form, combined with a phosphate group, a fatty acid (by an amide group: ceramide), a phosphocholine (sphingomyelin) or with more or less complex sugar groups (glycolipids).
They constitute the predominant class of terpenes. Their high unsaturation degree causes heat and light sensitivity and their intense colors make them the most ubiquitous pigments in plants and animals.
Molecules resulting from the condensation of an aminoalcohol and a fatty acid through an amide bond (N-acyl long-chain base). The alcohol function may be esterified by phosphoric acid (sphingomyelin) or linked to a glucide (glycosphingolipids).
This class of plant lipids is characterized by fatty acids esterified to a mono- or a dihydroxynitrile moiety, some of them being cyanogenic. They are mainly found in Sapindaceae.
Important group including long carbon chains with variations in degree and kind of branching, number of double bond, chain length. Some of them have also other functional groups (alcohol, ketone). They are found mainly esterified (waxes, glycerides, phospholipids, glycolipids, sterol esters, ceramides, polyesters, acyl-CoA). The most important element of cellular lipids.
Group including long carbon chains either normal or branched, saturated or not. They are found largely esterified (waxes).
The simplest lipids, formed of normal or branched carbon chains including paraffins and carotenoids. Several have an isoprenoid structure. Terpenes are included in this group. Some cyclic hydrocarbons are present in plants.
Alkyl ketones are constituents of
flavors but those with long carbon chain, alkenones,
are present in phytoplankton and sediments. Symmetrical ketones are found in
vegetal waxes and cyclic ketones have pheromone activities.
PHENOLIC LIPIDS
They are formed of a phenol, catechol, resorcinol or hydroquinone group, substituted or not, linked to a saturated or unsaturated straight chain.
PROSTANOIDS
AND RELATED COMPOUNDS
Prostanoids relates strictly to the products of the cyclooxygenase pathway and includes prostaglandins, prostacyclins, and thromboxanes. Leukotrienes, lipoxins, and various peroxy- or hydroxy-fatty acid derivatives are lipoxygenase products
Lipid quinones have one or two
cycles with normal or isoprenoid side chains of variable length and number of double bonds. They are
either vitamins (vitamin K), coenzymes (coenzyme Q or ubiquinones and plastoquinones), cytotoxic compounds (alkyl hydroquinones)
or naphthoquinone derivatives.
STEROIDS
Important
group of compounds based on the fundamental saturated tetracyclic hydrocarbon :
sterane. Derived from squalene, they may be considered as modified
triterpenes. They are classified into Sterols,
Brassinosteroids,
Bufadienolides,
Cardenolides,
Cucurbitacins,
Ecdysteroids, Sapogenins, Steroid alkaloids,
Withasteroids,
Bile acids, and
Hormonal steroids.
STEROLS
Group including cholesterol, the most widely occurring sterol in animal tissue, found as free alcohol or esterified with one fatty acid. Other forms are found in plants. Important constituents of cellular membranes are largely found circulating in plasma lipoproteins. The alcohol group may be esterified by a fatty acid (sterol esters), linked to a fatty alcohol (sterol alkyl ethers), esterified by sulfuric acid (sterol sulfate), or linked to a glucide (steryl glycoside). Sulfated steryl glycosides were also discovered in several species of starfish.
A wide group of natural hydrocarbons
whose structure is based on various but definite numbers of isoprene units. Many
of them are also oxygen-containing compounds (terpenoids or isoprenoids). They are constituents
of essential oils, resins, waxes, rubber,
and several bioactive molecules such as alkaloids, quinones, vitamins,
carotenoids and phenols
belong to that chemical group.
They are the main fat-soluble vitamins (vitamins A, D and E). They have up to three cycles with isoprenic side chains of variable length and number of double bonds.
Waxes are defined as fatty acid esters of fatty alcohols, both having a long carbon chain. Other esters have shorter carbon chains.
