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.
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Lipids


Lipids are fatty acids, waxes (fatty acids + alcohol), storage lipids (triacylglycerol) , membrane lipids (phospholipids: glycerophospholipids or sphingolipids and glycerolipids: sphingolipids), and sterols. Lipids can serve as signals, cofactors, and pigments.

 

Fatty acids

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) (Δ9) 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(Δ9)
palmitoleic acid
18:1(Δ9)
oleic acid
18:2(Δ9,12)
linoleic acid
18:3(Δ9,12,15)
α-linolenic acid
20:4(Δ5,8,11,14)
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 lipid representations

glycerophospholipids

 

glycolipids

Name Alcohol Name X
phosphatidic acid
H
ceramide
H
phosphatidylethanolamine

ethanolamine

sphingomyelin

phosphocholine

phosphatidylcholine

choline

glucosylcerebroside

glucose

phosphatidylserine
serine
lactosylceramide (globoside)

glucose-galactose

phosphatidylinositol-4,5-bisphosphate

myo-inositol-4,5-bisphosphate

 

ganglioside

complex oligosaccharide

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.

Here are a few observations:

 

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.

Common sterols and steroids

cholesterol

taurocholic acid

estradiol

testosterone

aldosterone

cortisol

 

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.

 

 

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