Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Genomic imprinting wikipedia , lookup
Gene regulatory network wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Ridge (biology) wikipedia , lookup
Gene expression profiling wikipedia , lookup
P-type ATPase wikipedia , lookup
Genome evolution wikipedia , lookup
Electron transport chain wikipedia , lookup
The genome of the bacterium E. coli has at least 427 genes coding for membrane transport proteins. This amounts to a startling 10% of all E. coli genes, and makes this the mostabundant type of gene in the genome. By way of comparison, the second most abundant type is biosynthetic genes, at 8% of the total. The large number of transport genes reflects the omnivorous appetite of E. coli for the wide variety of organic substrates it encounters in the complex biochemical stew of the mammalian gut. Another reason there are so many transport genes in E. coli is that often there are 2 or more redundant transport mechanisms for the same solute. A typical example is transport of the pentose, arabinose, which is transported by the ATPdependent ara F,G,H multi-component system and, independently, by the araE system which couples arabinose transport to proton transport. The equation for electrochemical potential, and a basic understanding of biochemical thermodynamics, properly applied, allow you to explain the existence of the two redundant arabinose transport systems. We notice that the two arabinose transport systems are redundant in the sense that they both transport arabinose, but they are not identical. The ara F, G, H multi-component system couples arabinose transport to ATP hydrolysis. The ara E system couples transport to proton transport (i.e. proton symport). Both systems use an exogenous source of free energy to drive endergonic arabinose uptake, therefore both are examples of active transport. Additionally, the binding constants (Km) of the two systems differ by several orders of magnitude. The ATP-dependent system exhibits high solute affinity, and the proton symport system relatively low affinity for arabinose. (The Km values are given in the diagram above.) Your task is to estimate (by calculation) the free energy change (in kJ per mole) for arabinose uptake by these two systems. Assume the intracellular arabinose concentration of 10 mM, and extracellular concentrations equal to the respective Km values of the two systems. NAME/S: Free energy required for arabinose uptake by the ATP-dependent system: __________kJ/mole Free energy required for arabinose uptake by the proton symport system: __________kJ/mole