tailieunhanh - Biochemistry, 4th Edition P56

Biochemistry, 4th Edition P56. 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 Can Be Learned from Metabolic Maps 513 the end product of heterotrophic carbon metabolism and CO2 is returned to the atmosphere for reuse by the photoautotrophs. In effect solar energy is converted to the chemical energy of organic molecules by photoautotrophs and heterotrophs recover this energy by metabolizing the organic substances. The flow of energy in the biosphere is thus conveyed within the carbon cycle and the impetus driving the cycle is light energy. What Can Be Learned from Metabolic Maps Metabolic maps Figure portray the principal reactions of the intermediary metabolism of carbohydrates lipids amino acids nucleotides and their derivatives. These maps are very complex at first glance and seem to be virtually impossible to learn easily. Despite their appearance these maps become easy to follow once the major metabolic routes are known and their functions are understood. The underlying order of metabolism and the important interrelationships between the various pathways then appear as simple patterns against the seemingly complicated background. The Metabolic Map Can Be Viewed as a Set of Dots and Lines One interesting transformation of the intermediary metabolism map is to represent each intermediate as a black dot and each enzyme as a line Figure . Then the more than 1000 different enzymes and substrates are represented by just two symbols. This chart has about 520 dots intermediates . Table lists the numbers of dots that have one or two or more lines enzymes associated with them. Thus this table classifies intermediates by the number of enzymes that act upon them. A dot connected to just a single line must be either a nutrient a storage form an end product or an excretory product of metabolism. Also because many pathways tend to proceed in only one direction that is they are essentially irreversible under physiological conditions a dot connected to just two lines is probably an intermediate in only one pathway and has .