BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 7. ENZYMOLOGY

7.7. Regulation of Metabolic Processes

A living Cell is an open system that continuously exchanges matter and energy with its external environment: it takes up nutrients that undergo transformations and are utilized as building blocks and a source of energy, while Metabolic waste products are excreted from The Cell. In a multicellular Organism, a cell responds not only to changes in its immediate environment but also to the functional activity of neighboring Cells. In doing so, it strives to maintain the constancy of its internal environment. This state is referred to as a steady state, or METABOLISM/37.html">Cellular Homeostasis.

A vast number of diverse Chemical Reactions constantly take place within the cell, forming metabolic pathways—sequential conversions of certain compounds into others. Metabolism is the totality of all metabolic pathways present in the organism's cells. Among them, two oppositely directed processes stand out: Catabolism and anabolism. Catabolism is The breakdown of complex substances into simpler ones accompanied by the release of energy. Anabolism is the synthesis of more complex substances from simpler ones. Metabolic pathways are coordinated with one another in terms of Location, time, and reaction rate. This coordination of all ongoing processes is ensured by complex and diverse regulatory mechanisms.