garrett and grisham, biochemistry, third edition chapter 8 lipids biochemistry by reginald garrett...
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Garrett and Grisham, Biochemistry, Third Edition
Chapter 8
Lipids
Biochemistry
by
Reginald Garrett and Charles Grisham
Garrett and Grisham, Biochemistry, Third Edition
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.
Garrett and Grisham, Biochemistry, Third Edition
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?
Garrett and Grisham, Biochemistry, Third Edition
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)
Garrett and Grisham, Biochemistry, Third Edition
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)
Garrett and Grisham, Biochemistry, Third Edition
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)
Garrett and Grisham, Biochemistry, Third Edition
Garrett and Grisham, Biochemistry, Third Edition
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
Garrett and Grisham, Biochemistry, Third Edition
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
Garrett and Grisham, Biochemistry, Third Edition
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
Garrett and Grisham, Biochemistry, Third Edition
Triacylglycerols - II
Other advantages accrue to users of triacylglycerols :
• Insulation • Energy without nitrogen • Metabolic water
Garrett and Grisham, Biochemistry, Third Edition
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.
Garrett and Grisham, Biochemistry, Third Edition
Garrett and Grisham, Biochemistry, Third Edition
Ether Glycerophospholipids
An ether instead of an acyl group at C-1
•Figure 8.8
1-alkyl 2-acyl-phosphatidylethanolamine (an ether glycerophospholipid)
Garrett and Grisham, Biochemistry, Third Edition
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)
Garrett and Grisham, Biochemistry, Third Edition
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.
Garrett and Grisham, Biochemistry, Third Edition
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.
Garrett and Grisham, Biochemistry, Third Edition
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
Garrett and Grisham, Biochemistry, Third Edition
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
Garrett and Grisham, Biochemistry, Third Edition
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.
Garrett and Grisham, Biochemistry, Third Edition
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.
Garrett and Grisham, Biochemistry, Third Edition
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
Garrett and Grisham, Biochemistry, Third Edition
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.
Garrett and Grisham, Biochemistry, Third Edition
An A-B cis steroid
Figure 8.19 The structure of cholesterol, shown with steroid ring designations and carbon numbering.