CH1131 Biomolecular Engrg Lipid Metabolism To Coordination Summary 2013
CH1131 Biomolecular Engrg Lipid Metabolism To Coordination Summary 2013
CH1131 Biomolecular Engrg Lipid Metabolism To Coordination Summary 2013
3
pathway, which requires a tetrahydrofolate derivative as the carrier for onecarbon transfer, is a target for cancer chemotherapy.
COORDINATION OF METABOLISM
How Are the Metabolic Pathways Connected? All metabolic pathways are related, and some metabolites appear in several pathways. Furthermore, many reactions of metabolism can take place simultaneously. The citric acid cycle plays a central role in metabolism, in both catabolic and anabolic pathways. The breakdown products of sugars, fatty acids, and amino acids all enter the citric acid cycle. How Can Biochemistry Help Us Understand Nutrition? The sources of substrates for catabolism and for anabolism are the nutrients derived from foodstuffs. In humans, the choice of diet becomes important in the interest of obtaining enough of essential nutrients while avoiding excesses of others, such as saturated fats, where excess is known to play a role in the development of health problems. In 1992, a food guide pyramid was published to explain nutrition basics to the public. This pyramid is currently being replaced by a newer version that recognizes the differences between various types of fats and carbohydrates instead of just sending the message that all fats are bad and all carbohydrates are good. What Are Hormones and Second Messengers? Sophisticated fine tuning of metabolic processes in multicellular organisms is possible through the actions of hormones and second messengers. In humans, a complex hormonal system has evolved that requires releasing factors (under the control of the hypothalamus), trophic hormones (under the control of the pituitary), and specific hormones for target organs (under the control of endocrine glands). Feedback control occurs at every level of the system. How Are Hormones Involved in the Control of Metabolism? When a hormone binds to its receptor on the plasma membrane of a target cell, it sets off a cascade of reactions by which second messengers elicit the actual cellular response. Two of the most important second messengers, cyclic AMP (cAMP) and phosphatidylinositol-4,5-bisphosphate (PIP2), activate protein kinases. Calcium ion is intimately involved in the action of PIP2. Hormonal triggering can be added to other levels of control of metabolism, such as allosteric activation and covalent modification, to ensure an efficient response to the needs of the organism. What Are the Many Effects of Insulin? Insulins primary job is to stimulate the glucose transporters in muscleparticularly the GLUT4 transporterto take up
4
glucose from the blood. In addition, it has a wide range of intracellular effects, such as switching off glycogen breakdown and turning on glycogen synthesis, stimulating glycolysis in the liver and muscle, turning off gluconeogenesis in the liver, and stimulating fatty-acid synthesis and storage. A recent discovery is that elevated levels of insulin in the blood may be related to Alzheimers disease.