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Biochemistry, 4th Edition P79

Biochemistry, 4th Edition P79. Continuing Garrett and Grisham's innovative conceptual and organizing framework, "Essential Questions," BIOCHEMISTRY guides students through course concepts in a way that reveals the beauty and usefulness of biochemistry in the everyday world. Streamlined for increased clarity and readability, this edition also includes new photos and illustrations that show the subject matter consistently throughout the text. New end-of-chapter problems, MCAT practice questions, and the unparalleled text/media integration with the power of CengageNOW round out this exceptional package, giving you the tools you need to both master course concepts and develop critical problem-solving skills you can draw upon. | 24.2 How Are Complex Lipids Synthesized 743 2 to 8 of the lipids in most animal membranes but breakdown products of PI including inositol-1 4 5-trisphosphate and diacylglycerol are second messengers in a vast array of cellular signaling processes. Dihydroxyacetone Phosphate Is a Precursor to the Plasmalogens Certain glycerophospholipids possess alkyl or alkenyl ether groups at the 1-position in place of an acyl ester group. These glyceroether phospholipids are synthesized from dihydroxyacetone phosphate Figure 24.23 . Acylation of dihydroxyacetone phosphate DHAP is followed by an exchange reaction in which the acyl group is removed as a carboxylic acid and a long-chain alcohol adds to the 1-position. This CH2 OH C O O I II ch2 o P O- I O- FIGURE 24.23 Biosynthesis of plasmalogens in animals. 1 Acylation at C-1 is followed by 2 exchange of the acyl group for a long-chain alcohol. 3 Reduction of the keto group at C-2 is followed by 4 and 5 transferase reactions which add an acyl group at C-2 and a polar head-group moiety as shown here for phosphoethanolamine and a 6 desaturase reaction that forms a double bond in the alkyl chain.The first two enzymes are of cytoplasmic origin and the last transferase is located at the endoplasmic reticulum. Dihydroxyacetone phosphate O R C O CH2 Dihydroxyacetone phosphate a acyltransferase CoA S CoASH C R CO O I II CH2 O P O- I O-1-Acyldihydroxyacetone phosphate HH R1 C C O CH2 O II R2 C O CH O I II ch2 O P O ch2ch2nh3 I O- Plasmalogen 1-Acyldihydroxyacetone phosphate synthase HO CH2CH2R1 1-Alkyl-2-acylglycero-phosphoethanolamine desaturase Q V -NADH 2 H2O O2 H R HgCHg-O CH2 R C O- II O C O O I II CH2 O P O- I O- 1-Alkyldihydroxyacetone phosphate 1-Alkyldihydroxyacetone NADPH H phosphate 3 oxidoreductase NADP R1CH2CH ch2 O II R2 C O C H O I II ch2 O P O ch2ch2nh3 I O- 1-Alkyl-2-acylglycero-3-phosphoethanolamine CDP-ethanolamine transferase R HgCHg O CH2 O HOCH O r2-c S CoA CoASH CH2 O P O- 1-Alkylglycerophosphate acyltransferase O- .