Lipids Lipids Lipids a heterogeneous class of naturally

Lipids • Lipids: Lipids a heterogeneous class of naturally occurring organic compounds (mainly esters) classified together on the basis of common solubility properties

Lipids • Lipids include – ESTERS – Triacylglycerols (triglycerides), phosphoacylglycerols (phospholipids), sphingolipids, glycolipids. – NON-ESTERS – cholesterol, steroid hormones, and bile acids – lipid-soluble vitamins, and prostaglandins

Waxes • Waxes are very water insoluble and high melting point. • They are widely distributed in nature as protective waterproof coatings on leaves, fruits, animal skin, fur, feathers and exoskeletons Prentice Hall c 2002 Chapter 9 8

Waxes • Esters of long-chain fatty acids and long chain monohydroxylic alcohols – from the Old English word weax = honeycomb

Triacylglycerols • Esters of glycerol with three fatty acids • Fatty acids are stored as neutral lipids, triaclyglycerols (TGs) • TGs are hydrophobic, stored in fat cells (adipocytes) Prentice Hall c 2002 Chapter 9 Structure of a triacylglycerol 10

Glycerophospholipids

Glycerophospholipids

Structures of glycerophospholipids Prentice Hall c 2002 Phosphatidylcholine (PC) Chapter 9 13

Structures of glycerophospholipids

Structures of glycerophospholipids Prentice Hall c 2002 Phosphatidylserine (PS) Chapter 9 15

Cardiolipin: • Two molecules of PA esterified through their phosphate groups to an additional molecule of glycerol is called cardiolipin

Importance of cardiolipin �Cardiolipin is found in bacteria and eukaryotes (inner mitochondrial membrane) �Cardiolipin is antigenic, and is recognized by antibodies raised against Treponema pallidum, the bacterium that causes syphilis

Sphingolipids • Sphingolipids - sphingosine is the backbone. Abundant in central nervous system tissues • Ceramides - fatty acyl group linked to sphingosine • Sphingomyelins - phosphocholine attached to ceramide • Cerebrosides - glycosphingolipids with one monosaccharide residue attached to ceramide • Galactosylcerebrosides - a single b-D-galactose as a polar head group • Gangliosides - contain oligosaccharide chains with N-acetylneuraminic acid (Neu. NAc) attached to a ceramide Prentice Hall c 2002 Chapter 9 18

(a) Sphingosine (b) Ceramides Prentice Hall c 2002 Chapter 9 19

Significance of Ceramide & sphingosine • Ceramide – A long-chain fatty acid is attached to the amino group of sphingosine through an amide linkage • Ceramides appear to be involved in the response to stress • sphingosine inhibits protein kinase C

Sphingomyelin • Amino alcohol sphingosine, rather than glycerol • The alcohol group at carbon 1 of sphingosine is esterified to phosphorylcholine • Sphingomyelin is an important constituent of the myelin of nerve fibers

Sphingomyelin degradation • Sphingomyelin is degraded in lysosomes by sphingomyelinase to give ceramide, • and ceramidase to give sphingosine • Niemann-Pick disease is due to sphingomyelinase deficiency

Glycolipids • Also known as glycosphingolipids • contain both carbohydrate and lipid components • Ceramides plus a long-chain fatty acid attached to the amino alcohol sphingosine �essential components of: �All membranes �Nerve cells

Glycolipids Significance �Glycosphingolipids are antigenic a source of blood group antigens �The carbohydrate portion of a glycolipid is the antigenic determinant �serve as cell surface receptors for cholera and tetanus toxins

• Structure of a galactocerebroside • Galactocerebroside—the most common cerebroside found in membranes • Glucocerebroside Prentice Hall c 2002 Chapter 9 26

Location • cerebrosides predominantly in the brain and peripheral nervous tissue

Ganglioside (sphingolipid) • found in the ganglion cells • Derivatives of ceramide oligosaccharides, and contain one or more molecules of NANA. • negatively charged at physiologic p. H provided by N-acetylneuraminic acid (NANA). • [NANA is also referred to as sialic acid. ] •