Lipids

Lipids List

Introduction

Lipids are a series of heterogeneous organic compounds that are only soluble in non-polar solvents such as ether, chloroform, and benzene, including fatty acids, phospholipids, sterols, sphingolipids, terpenes, and others. They occur naturally in most plants, animals, and microorganisms and are composed of carbon, hydrogen, and oxygen atoms. Lipids have many critical biological functions, such as acting as structural components of cell membranes, serving as a source of energy storage, and participating in signaling pathways ^[1]. Triglycerides, for instance, are lipids made up of glycerol bound with three fatty acid molecules and serve as energy storage depots. The structure is shown in Fig. 1.

Fig. 1 Structure of triglyceride.

Types of Lipids

The LIPID MAPS Consortium divides lipids into eight categories based on ketoacyl and isoprenyl "building blocks": fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, prenols, saccharolipids, and polyketides ^[1]. Each type of lipid compound is described in the following paragraphs.

• Fatty acyls

Fatty acyls refer to fatty acids and a range of their derivatives, such as alcohols, aldehydes, amines, and esters. Fatty acids are long aliphatic hydrocarbon chains with a carboxyl group at one end. They can be classified as short-chain, mid-chain, and long-chain fatty acids based on the length of the carbon chain, while also being classified as saturated, monounsaturated, and polyunsaturated fatty acids based on the degree of hydrocarbon chain saturation.

• Glycerolipids

Glycerolipids are esters formed by esterifying glycerol with fatty acids, where the glycerols could be mono-, di-, or tri-substituted and the fatty acids could be saturated or unsaturated. Glycerolipids can be classified into monoglycerides, diglycerides, and triglycerides based on the number of fatty acid units in the molecule.

• Glycerophospholipids

Glycerophospholipids are one of the important components of the double-layer membrane structure of cell membranes and are involved in the recognition and signaling of proteins by cell membranes. There are various types of glycerophospholipids, including choline, cardiolipin, and inositol.

• Sphingolipids

Sphingolipids are composed of a long-chain fatty acid, sphingosine, and a polar head group. In sphingolipids, the polar head group is attached to the hydroxyl group of sphingosine, while the fatty acid moiety forms an amide bond with the amino group. They are polar lipids and are the second-largest class of membrane lipids after phospholipids.

Fig. 2 Representative structures of fatty acyls, glycerolipids, glycerophospholipids, and sphingolipids ^[1].

• Sterols

Sterols are steroids with one hydrogen atom replaced by a hydroxyl group at 3-position of the carbon chain, which is an essential component of membrane lipids. The sterols in mammals, plants, and fungal cell membranes are bile acids, phytosterols, and ergosterols, respectively.

• Prenols

Prenols are synthesized from the five-carbon-unit precursors prenyl diphosphate and dimethylallyl diphosphate. They play an important role in the transport of oligosaccharides between cell membranes and also act as prohormones involved in the production of steroid hormones ^[2].

• Saccharolipids

Saccharolipids refer to compounds containing fatty acids linked directly to a sugar backbone. Saccharolipids in nature can be divided into glyceroglycolipids and glycosphingolipids according to the types of alcohol groups. The former is comprised of a glycerol backbone and at least one fatty acid, while the latter is composed of sphingosine linked to a non-lipid glycosyl moiety.

• Polyketides

Polyketides are synthesized by the polymerization of acetyl and propionyl subunits by classic enzymes as well as iterative and multimodular enzymes. There are a variety of structures in them, and some of them, such as erythromycin, tetracycline, and nystatin, form an important part of many antibiotics, fungicides, and anticancer medications.

Fig. 3 Representative structures of sterols, prenols, saccharolipids, and polyketides ^[1].

Alfa Chemistry provides our customers with structurally diverse lipid compounds including fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, prenols, saccharolipids, and polyketides. Please feel free to contact us for more information.

References:

1. Fahy, E. et al. Lipid classification, structures and tools. Biochimica et Biophysica Acta. 2011, 1811: 637–647.
2. Martano, C.; et al. Rapid high performance liquid chromatography-high resolution mass spectrometry methodology for multiple prenol lipids analysis in zebrafish embryos. Journal of Chromatography A. 2015, 1412: 59-66.