Metabolism regulatory mechanisms

Metabolic regulatory mechanisms have evolved so as to stabilize concentrations of key metabolites under a broad range of conditions. 

The intricate network of biochemical reactions occurring within the restricted volume of the liver cell requires subtly controlled metabolic regulatory mechanisms. (28) These occur on four levels (7.) at the molecular level, (2.) within the organelles, (3.) at the cellular level, and (4.) at the organ level. 

Cells are the fundamental units of life. They are functional entities, each of which is enclosed in a semipermeable membrane that varies in composition and function both over a single cell surface and between different cell types. There are two basic forms of cell prokaryotic and eukaryotic. Prokaryotes are most noted for their small sizes and relatively simple structures. Presumably because of these traits, in addition to their remarkably rapid reproduction rates and biochemical diversity, various prokaryotic species occupy virtually every ecological niche in the biosphere. In contrast, the most conspicuous feature of the eukaryotes is their extraordinarily complex internal structure. Because eukaryotes carry out their various metabolic functions in a variety of membrane-bound organelles, they are capable of a more sophisticated intracellular metabolism. The diverse metabolic regulatory mechanisms made possible by this complexity promote two important lifestyle features required by multicellular organisms cell specialization and intercellular cooperation. Consequently, it is not surprising that the majority of eukaryotes are multicellular organisms composed of numerous types of specialized cells. 

Such a pathway has both flow and direction. The enzymes catalyzing nonequilibrium reactions are usually present in low concentrations and are subject to a variety of regulatory mechanisms. However, many of the reactions in metabolic pathways cannot be classified as equilibrium or nonequilibrium but fall somewhere between the two extremes. 

To develop methods to identify individual or population susceptibility to environmental carcinogens, focusing on regulatory mechanisms for metabolism of carcinogens or repair mechanisms for carcinogen induced DNA damage between individuals or populations. 

This system has been widely used in uptake experiments to study transporter function. As Glazier et al. [47] have pointed out, an advantage of the system is that transporter function can be assessed independently of the contributions of metabolic systems. A disadvantage, however, is that all transporter regulatory mechanisms (many of which may be intracellular) are not preserved in this system, thus making the extrapolation of the results to in vivo situations somewhat difficult. 

Since transport across the syncytiotrophoblast layer is the rate-limiting step in the absorption of substances from the maternal circulation to the fetal, these cells can provide information on uptake processes which are subject to intracellular regulatory mechanisms or affected by intracellular metabolism. However, it is very difficult to isolate this layer because of its syncytial nature. As a result, the undifferentiated precursor cytotrophoblast cells have been isolated and cultured. These cells do not proliferate in culture, but aggregate and spontaneously differentiate into syncytiotrophoblasts [49],... 

Living systems are complex, ordered systems. This complexity and order is reflected in the molecules characteristic of life, in their interactions with each other, in the regulatory mechanisms that result from these interactions, and in the complex supramolecular structures characteristic of cells. Organization is also reflected in ordered metabolic and signaling pathways. Such complex, ordered structures and pathways are not characteristic of inanimate objects. 

Enzymes are biological catalysts—i. e substances of biological origin that accelerate chemical reactions (see p. 24). The orderly course of metabolic processes is only possible because each cell is equipped with its own genetically determined set of enzymes. It is only this that allows coordinated sequences of reactions (metabolic pathways see p. 112). Enzymes are also involved in many regulatory mechanisms that allow the metabolism to adapt to changing conditions (see p.ll4). Almost all enzymes are proteins. However, there are also catalytically active ribonucleic acids, the ribozymes" (see pp. 246, 252). 

The activities of all metabolic pathways are subject to precise regulation in order to adjust the synthesis and degradation of metabolites to physiological requirements. An overview of the regulatory mechanisms is presented here. Further details are shown on pp. 116ff. 

Metabolite flow along a metabolic pathway is mainly determined by the activities of the enzymes involved (see p. 88). To regulate the pathway, it is suf cient to change the activity of the enzyme that catalyzes the slowest step in the reaction chain. Most metabolic pathways have key enzymes of this type on which the regulatory mechanisms operate. The activity of key enzymes is regulated at three independent levels ... 

In all organisms, carbohydrate metabolism is subject to complex regulatory mechanisms involving hormones, metabolites, and coenzymes. The scheme shown here (still a simplified one) applies to the liver, which has central functions in carbohydrate metabolism (see p. 306). Some of the control mechanisms shown here are not effective in other tissues. 

Iron Metabolism - Inorganic Biochemistry and Regulatory Mechanism... 

When the steady state is disturbed by some change in external circumstances or energy supply, the temporarily altered fluxes through individual metabolic pathways trigger regulatory mechanisms intrinsic to each pathway. The net effect of all these adjustments is to return the organism to a new steady state—to achieve homeostasis. 

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