Breakdown of energy expenditure at the level of a single cell?

Question

The metabolic rate measures how much energy an organism **expends** over a unit of time. Its breakdown for the human body in terms of its functions is well documented : so much for the heart, for the brain, etc.In [West et al, 2002](www.pnas.org/content/99/suppl_1/2473.abstract) I have found an estimate for the metabolic rate of a single cell. But how does this breakdown in terms of elementary functions in the cell?E.g., how much of the energy made available from nutrients is used in the process of replicating genome, of expressing proteins, of trafficking...?Following Jeremy Kemball's link suggestions, I find in [this paper](http://www.ncbi.nlm.nih.gov/pubmed/7492307%2C7708012?dopt=Abstract) the fraction of ATP consumption for the following processes: Protein synthesis 0.34 Na+/K+ ATPase 0.16 Ca2+ ATPase 0.17 RNA/DNA synthesis 0.25 Unidentified 0.09(which adds up to 1.01 rather than 1 for spurious reasons). Their measurement is indirect, based on $O_2$ consumption for an assumed steady-state regeneration of ATP. I wonder how GTP-based processes are accounted for? Or are they negligible compared to ATP ones?This is for a specific cell type, rat thymocyte, is there a reason to expect that this will be hugely different for say a fibroblast? Also, they stimulate their thymocyte with concanavalin A. I understood they are not getting RNA/DNA consumption signal without Con-A, but didn't get why it would be so.Finally, what would be in the remaining 9% ? One candidate for ATP consumption suggested by Jeremy Kemball is actin turnover, I guess it fits only in the "unidentified" line. Tubulin turnover is a GTP process, not sure about intermediate filaments (do they turnover?). All ATP-molecular motors (myosin, kinesin, dynein at least?) have to be there too. What else? I am particularly interested in the total amount of ATP energy that goes to myosin.

Answer 1

The total ATP allocated to myosin activity depends heavily on the specific cell type and physiological state. In cells requiring significant contractile activity (e.g., muscle cells or motile fibroblasts), myosin ATP consumption can be substantial. For non-muscle cells, such as thymocytes, myosin consumes a smaller portion of ATP, likely contributing to the "unidentified" fraction alongside actin turnover.