Biochemistry, 4th Edition P27. 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. | What Are the Structures and Chemistry of Glycerophospholipids 223 A DEEPER LOOK Polar Bears Prefer Nonpolar Food The polar bear is magnificently adapted to thrive in its harsh Arctic environment. Research by Malcolm Ramsay at the University of Saskatchewan in Canada and others has shown that polar bears eat only during a few weeks out of the year and then fast for periods of 8 months or more consuming no food or water during that time. Eating mainly in the winter the adult polar bear feeds almost exclusively on seal blubber largely composed of triacylglycerols thus building up its own triacylglycerol reserves. Through the Arctic summer the polar bear maintains normal physical activity roaming over long distances but relies entirely on its body fat for sustenance burning as much as 1 to kg of fat per day. It neither urinates nor defecates for extended periods. All the water needed to sustain life is provided from the metabolism of triacylglycerols because oxidation of fatty acids yields carbon dioxide and water . Ironically the word Arctic comes from the ancient Greeks who understood that the northernmost part of the earth lay under the stars of the constellation Ursa Major the Great Bear. Although unaware of the polar bear they called this region Arktikos which means the country of the great bear. glycerols are normally soluble in benzene chloroform ether and hot ethanol. Although triacylglycerols are insoluble in water monoacylglycerols and diacylglycerols readily form organized structures in water see Chapter 9 owing to the polarity of their free hydroxyl groups. Triacylglycerols are rich in highly reduced carbons and thus yield large amounts of energy in the oxidative reactions of metabolism. Complete oxidation of 1 g of triacylglycerols yields about 38 kJ of energy whereas proteins and carbohydrates yield only about 17 kJ g. Also their hydrophobic nature allows them to aggregate in highly anhydrous forms whereas polysaccharides and proteins are highly .
