Metabolism defined

Biochemical studies follow several themes. For example, investigations can be focussed on the chemical structures of molecules, (for example the structure of glycogen, DNA or protein conformation) or the structural inter-relationship between molecules (e.g. enzymes with their substrates, hormones with their receptors). The other branch of biochemical enquiry is into those numerous dynamic events known collectively as metabolism , defined here as all of the chemical reactions and their associated energy changes occurring within cells . The purpose of metabolism is to provide the... 

Several processes involving the continuous feeding in activated reactants supplying chemical energy have been proposed to lead to the emergence of proto-metabolisms (otherwise called chemo-metabolisms), defined as a sequence of thermodynamically favorable chemical reactions (usually cyclic) through which more evolved species could have been produced, and that could have been the starting point from which life developed. 

Figure k. Three internal compartment serial model for calciiim metabolism defining metabolic parameters. 

Outline the formation of phosphoglycolate by the oxygenase reaction of rubisco, and follow its subsequent metabolism. Define photorespiration. 

A model can be defined as a set of relationships between the variables of interest in the system being investigated. A set of relationships may be in the form of equations the variables depend on the use to which the model is applied. Therefore, mathematical equations based on mass and energy balances, transport phenomena, essential metabolic pathway, and physiology of the culture are employed to describe the reaction processes taking place in a bioreactor. These equations form a model that enables reactor outputs to be related to geometrical aspects and operating conditions of the system. 

Alveolar ventilation supplies O2 to the bloodstream while alveolar capillary perfusion provides alveolar gas with COj. Resting individuals consume approximately 250 mL 02/min and produce approximately 200 ml. COi/min because, stoichiometrically, metabolic processes require a greater supply of O, than the quantity of CO2 produced. Defining the respiratory exchange ratio, R, as... 

Neurons have three parts the cell body and dendrites, the axon, and axon terminals. The cell body contains the nucleus and the organelles needed for metabolism, growth, and repair. The dendrites are branched extensions of the cell body membrane. The axon is a long, thin structure which transfers electrical impulses down to the terminals. The axon divides into numerous axon terminals and it is in this specialized region that neurotransmitters are released to transmit information from one neuron to its neighbors. The synapse has been defined as the space between two subsequent interrelated neurons. ... 

It is hoped that these volumes will be useful not only to the chemist who wishes to carry out synthesis in the steroid field, but also to the broader group of organic chemists who are interested in carrying out selective and stereo-chemically defined reactions, as well as protective chemistry on extraneous functional groups, during a broad range of synthetic applications. The chapter on the introduction of deuterium and by inference tritium into steroids was included because of the importance of this technique in mechanistic and metabolic studies both in the steroid and nonsteroid field. 

Define the differences in carbon and energy metabolism between photoautotrophszxidphotoheterotropHs, and between ehemoau-totropHs and ehemoheterotropHs. 

Cell growth and metabolic activities are similarly described as a simple chemical reaction. It is also necessary to establish a definite formula for dry cell matter. The elemental composition of certain strains of microorganism is defined by an empirical formula CHaO/3Ns. The general biochemical reaction for biomass production is based on consumption of organic substrate, as shown below. Substrate oxidation is simplified in the following biochemical oxidation ... 

Hyperthyroidism (thyrotoxicosis), defined as excessive thyroid activity, causes a state of thyroid hormone excess (thyrotoxicosis) characterized by an increased metabolic rate, increase in body temperature, sweating, tachycardia, tremor, nervousness, increased appetite and loss of weight. Common causes of hyperthyroidism are toxic multinodular goiter, toxic adenoma or diffuse toxic goitre ( Graves disease). Antithyroid diugs (methimazol, carbimazole, propylthiouracil) block thyroid hormone production and are hence suitable for the treatment of hyperthyroidism. 

Epilepsy may be defined as a permanent, recurrent seizure disorder. Examples of the known causes of epilepsy include brain injury at birth, head injuries, and inborn errors of metabolism, hi some patients, the cause of epilepsy is never determined. 

A three-dimensional meshwork of proteinaceous filaments of various sizes fills the space between the organelles of all eukaryotic cell types. This material is known collectively as the cytoskeleton, but despite the static property implied by this name, the cytoskeleton is plastic and dynamic. Not only must the cytoplasm move and modify its shape when a cell changes its position or shape, but the cytoskeleton itself causes these movements. In addition to motility, the cytoskeleton plays a role in metabolism. Several glycolytic enzymes are known to be associated with actin filaments, possibly to concentrate substrate and enzymes locally. Many mRNA species appear to be bound by filaments, especially in egg cells where they may be immobilized in distinct regions thereby becoming concentrated in defined tissues upon subsequent cell divisions. 

In both intermediate and maximum rates of respiration, control is distributed between several different steps, including the activity of the adenine nucleotide translocator (Groen et al., 1983). It is now recognized that the idea of a simple rate-limiting step for a metabolic pathway is simplistic and that control is shared by all steps although to different extents (Kacserand Bums, 1978 Fell, 1992). Each step in a pathway has a flux control coefficient (FCC) defined as ... 

Finally, an outline of how the same approach to modeling can be applied to questions of nitrogen metabolism and to food chains in ecosystems is presented. We would argue that the value of such an approach lies at least as much in helping to better define issues, and in suggesting new, testable hypotheses, than in providing explanations which may rest on oversimplified assumptions. 

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