Biochemistry and Molecular Biology Resource   Web Lessons

Eric C. Niederhoffer, Ph.D. Associate Professor of Biochemistry and Molecular Biology Southern Illinois University School of Medicine 600 Agriculture Drive, Carbondale, IL 62901-6503 Rm 112 Lindegren, 618-453-6467 eniederhoffer@siumed.edu Copyright 2000- , E.C. Niederhoffer. All Rights Reserved. All trademarks and copyrights are the property of their respective owners.

Generic fatty acid representation

Fatty acids are hydrocarbon chains with a carboxylic acid group. The total number of carbons varies from 4 to 36 with the typical length comprising 12 to 24 carbons. The nomenclature (N:n) indicates the number of carbon atoms:number of double bonds, with the symbol delta followed by superscript number(s) () indicating the position of the first carbon involved in each double bond.

Typical fatty acids

Carbon skeleton	Structure	Common name
12:0		lauric acid
14:0		myristic acid
16:0		palmitic acid
18:0		stearic acid
20:0		arachidic acid
24:0		lignoceric acid
16:1()		palmitoleic acid
18:1()		oleic acid
18:2()		linoleic acid
18:3()		-linolenic acid
20:4()		arachidonic acid

Waxes

Generic wax representation

Waxes are esters of long-chain (carbons vary from 14 to 36) saturated and unsaturated fatty acids with long chain (carbons vary from 16 to 30) alcohols.

Storage lipids

Generic triacylglycerol representation

Storage lipids are generally triacylglycerols (neutral lipids). The general structure is based upon glycerol (a triol), which has been esterified with three fatty acids. Triacylglycerols are stored as oil droplets within cells and the glycerol and fatty acids may be released by the action of enzymes (lipases) to be metabolized to create energy (ATP).

Membrane lipids

Membrane lipids are a broad group consisting of phospholipids (glycerophospholipids, sphingoplipids with phosphate) and glycolipids (sphingolipids lacking phosphate). Sphingolipids are based upon sphingosine. As you can observe, sphingolipids may include or lack a phosphate group. The X group in glycolipids (sphingolipids) is a mono-, di, tri, tetra, or oligosaccharide.

• Hydrolysis (cleavage) of phosphatidylinositol-4,5-bisphosphate results in diacylglycerol (DAG) and inositol-1,4,5-trisphosphate (IP₃), which are important second messengers (signal transduction).
• Arachidonic acid may be released from membrane phospholipids and processed to generate prostaglandins, thromboxanes, and leukotrienes (inflammatory signals).
• Glycolipids containing specific complex oligosaccharides comprise the human blood groups (surface antigens) and are important in transfusions.

Sterols

Generic sterol representation

Sterols have as their core a fused four ring structure (the A, B, C, and D rings). Various groups are added to the core structure to generate other important molecules.

The most common sterols are derived from cholesterol. They include bile acids and steroids. Cholesterol is an important membrane lipid in cells. The bile acids are used to process dietary fats. The steroids serve as hormonal signals for various cell processes. Steroids bind to internal receptors associated with the expression of important genes.