5V at 1A is 5W. If the efficiency of the stepup converter is perfect (impossible) then two 1.5V alkaline AA cells would need an output of 1.67A if the cells are new and would need an output of 2.5A when they are run down a little to 1V each.
Here is a graph from Duracell that shows two alkaline AA cells produce 1.5V each for only a few seconds when the current is only 1A and drop to 1V each in a few minutes.
Here is a graph from Energizer showing than AA Ni-MH rechargeable cells delivers high current much better than alkaline.