Garrett and Grisham, Biochemistry, Third Edition Chapter 8 Lipids Biochemistry by Reginald Garrett and Charles Grisham

Garrett and Grisham, Biochemistry, Third Edition

Chapter 8

Lipids

Biochemistry

by

Reginald Garrett and Charles Grisham


Essential Question

• What is the structure, chemistry, and biological function of lipids?

• Lipids – low solubility in water and high solubility in nonpolar solvents.

• The hydrophobic nature of lipids allows membranes to act as effective barriers to more polar molecules.


Outline• What Is the Structure and Chemistry of Fatty Acids?• What Is the Structure and Chemistry of

Triacylglycerols? • What is the Structure and Chemistry of

Glycerophospholipids?• What Are Sphingolipids, and How Are They Important

for Higher Animals? • What Are Waxes, and How Are They Used?• What Are Terpenes, and What Is Their Relevance to

Biological Systems?• What Are Steriods, and What Are Their Cellular

Functions?


Classes of Lipids

All biological lipids are amphipathic (containing both polar and nonpolar

groups).

• Fatty acids • Triacylglycerols • Glycerophospholipids • Sphingolipids • Waxes • Isoprene-based lipids (including steroids)


8.1 - Fatty acids

Know the common names and structures for fatty acids up to 20 carbons long

• Saturated – Lauric acid (12 C) – Myristic acid (14 C) – Palmitic acid (16 C) – Stearic acid (18 C) – Arachidic acid (20 C)


Fatty acids - II

• Unsaturated fatty acids

– Palmitoleic acid (16:1)

– Oleic acid (18:1)

– Linoleic acid (18:2) -Linolenic acid (18:3) -Linolenic acid (18:3)

– Arachidonic acid (20:4)



Fatty acids - III

Structural consequences of unsaturation

• Saturated chains pack tightly and form more rigid, organized aggregates (i.e., membranes)

• Unsaturated chains bend and pack in a less ordered way, with greater potential for motion


Source Lauric & Myristic Palmitic Stearic Oleic Linoleic

Beef 5 24-32 20-25 37-43 2-3Milk 25 12 33 3Coconut 74 10 2 7Corn 8-12 3-4 19-49 34-62Olive 9 2 84 4Palm 39 4 40 8Safflower 6 3 13 78Soybean 9 6 20 52Sunflower 6 1 21 66

Fatty acids in Food: saturated vs. unsaturated

Fatty acid compositions of some dietary lipids


8.2 - Triacylglycerols

Also called triglycerides

• A major energy source for many organisms

• Why?

– Most reduced form of carbon in nature

– No solvation needed

– Efficient packing


Triacylglycerols - II

Other advantages accrue to users of triacylglycerols :

• Insulation • Energy without nitrogen • Metabolic water


8.3 - Glycerophospholipids

Glycerophospholipids are phospholipids but not necessarily vice versa.

• Know the names and structures in Figure 8.6 • Understand the prochirality of glycerol • Remember that, if phospholipid contains

unsaturation, it is at the 2-position.



Ether Glycerophospholipids

An ether instead of an acyl group at C-1

•Figure 8.8

1-alkyl 2-acyl-phosphatidylethanolamine (an ether glycerophospholipid)


Ether Glycerophospholipids• Platelet activating factor (PAF) is an ether glycerophospholipid.

• PAF is a potent biochemical signal molecule • Note the short (acetate) fatty acyl chain at the C-2 position in PAF.• PAF is much more water soluble, functions as a soluble messenger in signal transduction.

Figure 8.9 1-alkyl 2-acyl-phosphatidylcholine (PAF)


8.4 – Sphingolipids 神經鞘脂質

Base structure is sphingosine.

•Sphingosine is an 18-carbon amino alcohol. •Ceramides are amide linkages of fatty acids to the nitrogen of sphingosine. •Glycosphingolipids are ceramides with one or more sugars in beta-glycosidic linkage at the 1-hydroxyl group.


SphingolipidsBase structure is sphingosine.

•Sphingosine is an 18-carbon amino alcohol. •Ceramides (神經醯胺 ) are amide linkages of fatty acids to the nitrogen of sphingosine. •Glycosphingolipids are ceramides with one or more sugars in beta-glycosidic linkage at the 1-hydroxyl group.

Figure 8.11 Formation of an amide linkage between a fatty acid and sphingosine produces a ceramide.


Sphingolipids

Backbone of sphingosine: 18-carbon amino alcohol with C-C trans double bond

Ceramide: sphingosine with fatty acid in amide linkage Sphingomyelins: alcohol esterified to phosphoceramide

Choline Ethanolamine

Glycosphingolipids: ceramide with sugars in -glycosidic linkage

Cerebroside: Sugar is glucose or galactose. Sulfatide: Sugar is galactose with sulfate esterified at carbon 3 of galactose. Gangliosides: ceramide with three or more sugars including sialic acid


8.5 - Waxes

Esters of long-chain alcohols with long-chain fatty acids

• Highly insoluble • Animal skin and fur are wax-coated • Leaves of many plants • Bird feathers


8.5 WaxesEsters of long-chain alcohols with long-chain

fatty acids

• highly insoluble • Animal skin and fur are wax-coated .• leaves of many plants • bird feathers

Figure 8.15 An example of a wax. Oleoyl alcohol is esterified to stearic acid in this case.


8.6 - Terpenes

Based on the isoprene structure

• Know nomenclature • Understand linkage modes (Figure 8.16) • See structures in Figure 8.17 • All sterols (including cholesterol) are terpene-

based molecules. • Steroid hormones are terpene-based.


8.6 Terpenes

Based on the isoprene structure

• Know nomenclature • All sterols (including cholesterol) are

terpene-based molecules. • Steroid hormones are terpene-based.

Figure 8.16


8.7 - Steroids

• Based on a core structure consisting of three 6-membered rings and one 5-membered ring, all fused together.

• Cholesterol is the most common steroid in animals and precursor for all other steroids in animals.

• Steroid hormones serve many functions in animals - including salt balance, metabolic function and sexual function.


An A-B cis steroid

Figure 8.19 The structure of cholesterol, shown with steroid ring designations and carbon numbering.

Documents

Garrett and Grisham, Biochemistry, Third Edition Chapter 8 Lipids Biochemistry by Reginald Garrett and Charles Grisham