Part 2: Fats Prepared by: Dr A. Riasi ( Isfahan University of Technology ) Reference: Lehninger Biochemistry Advance Biochemistry Isfahan University of Technology

Biological Lipids  Lipids are divides to three original groups: Fats and oils Phospholipids and sterols Other lipids

Storage lipids  Fatty acids are carboxylic acids: CH3(CH2)n-COOH

Storage lipids  A few contain three-carbon rings, hydroxyl groups, or methyl group branches.  A simplified nomenclature for these compounds specifies the chain length and number of double bonds.

Storage lipids  The positions of any double bonds are specified by superscript numbers following (Δ).  A 20-carbon fatty acid with one double bond between C-9 and C-10 and another between C-12 and C-13 is designated as C20:2(Δ 9,12 ).

Storage lipids  The poly unsaturated fatty acid of Arachidonic [20:4 (Δ 5,8,11,14 )] is an exception to this generalization. CH3(CH2)4CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOH

Storage lipids CH3-(CH2)7-CH=CH-(CH2)4-CH2-CH2-CH2-COOH ω n Δ αβγ

Storage lipids  In nearly all naturally occurring unsaturated fatty acids, the double bonds are in the cis configuration.

Storage lipids

11 What are the differences between α Linolenic acid and γ Linolenic acids?

Storage lipids Comparison of the satutare Stearic acid (left), trans isomer (middle) Elaidic acid and the cis-isomer (right) Oleic acid.

Storage lipids

 Most naturally occurring triacylglycerols are mixed.  They contain two or more different fatty acids. Storage lipids

 Vegetable oils are converted industrially into solid fats by catalytic hydrogenation. Storage lipids

 Biological waxes are esters of: Long-chain (C14 to C36) saturated Unsaturated fatty acids with long-chain (C16 to C30) alcohols. Storage lipids

 There are different generals types of membrane lipids: Glycerophospholipids Galactolipids and Solpholipds Archaebacterial tetraether lipids Sphingolipids Sterols Phospholipids and sterols

 Glycerophospholipids and some sphingolipids are named phospholipids. Phospholipids and sterols

 Other sphingolipids are the glycolipids. Phospholipids and sterols

 The polar alcohol may have different charge: Negatively charged: phosphatidylinositol 4,5- bisphosphate Neutral: phosphatidylserine Positively charged: phosphatidylcholine or phosphatidylethanolamine Phospholipids and sterols

 The fatty acids in glycerophospholipids can be any of a wide variety  A given phospholipid may consist of a number of molecular species, each with its unique complement of fatty acids. Phospholipids and sterols

 Some animal tissues are rich in ether lipids.  In ether lipids one of the two acyl chains is attached to glycerol in ether linkage. Phospholipids and sterols

 Two kind of ether lipids: Ether-linked chain is saturated Ether-linked chain is unsaturated Phospholipids and sterols

 The functional significance of ether lipids in these membranes is unknown.  The ether lipid, platelet-activating factor, is a potent molecular signal. It is released from leukocytes called basophils. Phospholipids and sterols

 The galactolipids & Solpholipids are predominate in plant cells. Phospholipids and sterols

 The archaebacteria, most of which live in ecological niches with extreme condition: Low pH High ionic strength High temprature Phospholipids and sterols

 Sphingolipids, have a polar head group and two nonpolar tails.  Unlike glycerophospholipids and galactolipids they contain no glycerol. Phospholipids and sterols

 Sphingolipids are composed of: one molecule of the long-chain amino alcohol one molecule of a long-chain fatty acid a polar head group Phospholipids and sterols

 Carbons C-1, C-2, and C-3 of the sphingosine molecule are structurally analogous to the three carbons of glycerol in glycerophospholipids. Phospholipids and sterols

 There are three subclasses of sphingolipids, all derivatives of ceramide but differing in their head groups: Sphingomyelins, Neutral (uncharged) glycolipids, Gangliosides. Phospholipids and sterols

 Sterols are structural lipids present in the membranes of most eukaryotic cells.  Cholesterol is the major sterol in animal tissues, is amphipathic.  Similar sterols are found in other eukaryotes: stigmasterol in plants and ergosterol in fungi. Phospholipids and sterols

 The sterols serve as precursors for a variety of products with specific biological activities. Steroid hormones Bile acids to make them more readily accessible to digestive lipases. Phospholipids and sterols

 Steroids are oxidized derivatives of sterols  Steroid hormones move through the bloodstream (on protein carriers) from their site of production to target tissues, where they enter cells, bind to highly specific receptor proteins in the nucleus. Phospholipids and sterols

 The major groups of steroid hormones are the male and female sex hormones and the hormones produced by the adrenal cortex. Phospholipids and sterols

 Prednisone and prednisolone are steroid drugs with potent antiinflammatory activities.  They have a variety of medical applications, including the treatment of asthma and rheumatoid arthritis. Phospholipids and sterols

 Eventually the fat-soluble group was resolved into the four vitamin groups A, D, E, and K, all of which are isoprenoid compounds.  Two of these (D and A) serve as hormone precursors. Phospholipids and sterols

 Vitamin D3, also called cholecalciferol, is normally formed in the skin from 7- dehydrocholesterol in a photochemical reaction driven by the UV component of sunlight. Phospholipids and sterols

 Vitamin D3 is not itself biologically active, but it is converted by enzymes in the liver and kidney to 1,25-dihydroxycholecalciferol.  Vitamin D2 (ergocalciferol) is a commercial product formed by UV irradiation of the ergosterol of yeast. Phospholipids and sterols

 Vitamin D2 is structurally similar to D3, with slight modification to the side chain attached to the sterol D ring. Phospholipids and sterols

 Like steroid hormones, the product of vitamin D metabolism, 1,25-dihydroxycholecalciferol, regulates gene expression—for example, turning on the synthesis of an intestinal Ca2- binding protein. Phospholipids and sterols

 Vitamin A (retinol) in its various forms functions as a hormone.  The vitamin A derivative, retinoic acid, regulates gene expression in the development of epithelial tissue, including skin. Phospholipids and sterols

 The vitamin A derivative, retinal, is the pigment that initiates the response of cells of the retina to light, producing a neuronal signal to the brain. Phospholipids and sterols

 In vertebrates, -carotene, the pigment that gives carrots, sweet potatoes, and other yellow vegetables their characteristic color, can be enzymatically converted to vitamin A. Phospholipids and sterols