The need for energy

Quite apart from obvious work output, the body has a considerable requirement for energy, even at rest. Only about one-third of the average person s energy expenditure is for voluntary work (section 5.1.3). Two-thirds is required for maintenance of the body s functions, homeostasis of the internal environment and metabolic integrity. 

Part of this basal energy requirement is obvious — the heart beats to circulate the blood respiration continues and there is considerable electrical activity in nerves and muscles, whether they are working or not. These processes require a metabolic energy source. Less obviously, there is also a requirement for energy for the wide variety of biochemical reactions occurring all the time in the body laying down reserves of fat and carbohydrate (section 5.6) turnover of tissue proteins (section 9.2.3.3) transport of substrates into, and products out of, cells (section 3.2.2) and the production and secretion of hormones and neurotransmitters. 

Energy expenditure is measured by the output of heat from the body (section 5.1). The unit of heat used in the early studies was the calorie — the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius. The calorie is still used to some extent in nutrition in biological systems the kilocalorie, kcal (sometimes written as Calorie with a capital C) is used. One kilocalorie is 1000 calories (10 cal), and hence the amount of heat required to raise the temperature of 1 kg of water through 1 degree Celsius. 

Correctly, the joule is used as the unit of energy. The joule is an SI unit, named after James Prescott Joule (1818-89), who first showed the equivalence ofheat, mechanical work and other forms of energy. In biological systems, the kilojoule (kj = 10 J = 1000 J) and megajoule (1 MJ = 10 J = 1,000,000 J) are used. 

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K. Caldeira, A.K. Jain, M.I. Hoffert, Climate sensitivity uncertainty and the need for energy without C02 emission, Science 299 (2003) 2052-2054. 

In view of the energy crisis, the need for energy innovation and the moves to limit the oil companies, it is too bad we do not understand this area very well. Anti-trust actions do have profound effects on innovation. Foster and Gluck refer to government moves to break up IBM and Bell without any thought of the impact on these one billion dollar research organizations. It is interesting that the authors refer to a Senate Bill authored by the... 

Oxidation of fatty acids consumes a precious fuel, and it is regulated so as to occur only when the need for energy requires it. In the liver, fatty acyl-CoA formed in the cytosol has two major pathways open to it (1) J3 oxidation by enzymes in mitochondria or (2) conversion into triacylglycerols and phospholipids by enzymes in the cytosol. The pathway taken depends on the rate of... 

Compared to water-another green solvent which is frequently adopted as a dispersing medium in industrial heterogeneous polymerizations-scC02 eliminates the need for energy-intensive drying processes, as the polymer product can... 

Figure 1.5. Schematic structure of world economies. From EIA (2005), WEO (2002, 2004, 2005). Percent annual growth in the need for energy resources is shown in the respective regions.

The need for energy is so enormous that conventional, long-discussed sources will not be enough. 

The need for energy by the cell regulates the TCA cycle, which acts in concert with the electron transfer chain and the ATPase to produce ATP in the inner mitochondrial membrane. The cell has limited amounts of ATP, ADP,... 

Many features of signal-transduction pathways are ancient. For example, cAMP signals the need for energy in prokaryotes as well as eukaryotes, although the mechanisms for detecting cAMP are different. Similarly, the GTP-binding proteins—the subunits of the hetero-trimeric G proteins and the members of the Ras family—are part of an... 

Fells, I., The need for energy. Europhysics News, November/December 1998, p. 193. 

AMINO ACIDS On the market there are preparations containing 18 essential and non-essential amino-acids which are required for synthesis of the proteins of the body. The balance between the amino-acids is such that a positive nitrogen balance is obtained both in nutrition over long time periods and in the postoperative phase. In order that the amino-acids should be used optimally for protein synthesis, the need for energy should be supplied... 

This section presents and discusses the practical issues associated with use of the constraint technique presented in this chapter. Some of these key issues include the need for energy conservation, techniques for ensuring the simulation initially proceeds along the compressive branch of the Rayleigh line, criteria for the choice of the empirical mass-like parameter Q in Eq. (8), and criteria for the choices of computational cell size and simulation duration. 

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