Basal metabolic rate contributions

The quantitative importance of each pathway varies from one tissue to another and from one protein to another. Although hydrolysis of the peptide bonds does not involve ATP, the various processes of protein degradation require considerable expenditure of energy, possibly more than is required for protein synthesis. It is not suprising, therefore, that protein turnover contributes at least 20% to resting energy expenditure (basal metabolic rate). 

The only useful contribution of endocrine studies to diagnosis has been in the condition dystrophia myotonica, with its 80% incidence of eventual primary testicular atrophy in males. Many workers (Cl, Dl, G7, K15) have reported the urinary excretion of 17-ketosteroids in this condition to be subnormal in males, and even in females to be in the low normal range. Recent thorough investigations, however (B22, D18), have disclosed that, apart from an unexplained frequently low basal metabolic rate and the consequences of eventual testicular atrophy, there seems to be no reason to suppose that adrenal cortical, thyroidal, ovarian, and pituitary functions are other than normal in dystrophia myotonica. A majority of males examined had been fertile, and most women had brought one or more normal full-term pregnancies to spontaneous delivery. 

Metabolism would be extremely complex if coupled processes directly, however. Instead use an intermediate energy carrier ATP. Thus, catabolic processes make ATP which can then be used for anabolic processes, locomotion, pumping ions across cell membranes (major contribution to basal metabolic rate or BMR), etc. Note that ATP is not used to store energy however. (Often compared to electricity s role in our culture). 

The three main components are basal metabolic rate (BMR), which constitutes 60% of daily whole body expenditure physical activity, which generally contributes -30% of the total and diet-induced thermogenesis, making up the remaining 10%. These proportions vary among individuals, but the figures do illustrate the general dominance of BMR in the daily metabolic rate. 

Basal metabolic rate is the energy expenditure by the body when at rest, but not asleep, under controlled conditions of thermal neutrality, and about 12 hours after the last meal. It is the energy requirement for the maintenance of metabolic integrity, nerve and muscle tone, circulation and respiration (see Figure 1.2 for the contribution... 

Darveau et al. (2002, 2003) propose that the relationship between body mass and metabolic rate reflects the contribution of multiple factors - ATP-utilization processes in parallel, supply processes in series - that each have different power functions. This hierarchical layering results in an allometric cascade that has different scaling implications for different measures of metabolism. They contend that only a multiple-factor account, and not West s (or any) single-cause account, can explain the scaling difference between basal and maximum metabolic rate (Bishop, 1999). However, the mathematical formulation of their model has been severely criticized (Banavar etal., 2003 West etal., 2003), and in any case it does not provide an account of why individual processes scale as power functions of mass or why the causal cascade results in a whole-organism metabolism that approximates the 3/4 rule (Bokma, 2004 West et al., 2003 West and Brown, 2004). 

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