Comparison of growth factor receptor signalling continued: This figure shows a comparison of ERK signalling from the NGF and mutated EGF receptors. At the top, a schematic of the NGF induced ERK pathway is shown in (A), with the Rap1 pathway highlighted in red as it is the key process in generating a sustained response, this is demonstrated in (B). All the lines in (B) represent simulated active ERK levels over 60 minutes. The blue line represents active ERK levels from the normal NGF model, the green line represents active ERK levels after the SOS negative feedback loop is knocked out, whereas the red line represents active ERK levels after the Rap1 pathway is knocked out. Almost identical simulation results are found for the mutated EGFR model (C, D), where the Rap1 pathway is again found to be the key process in generating a sustained signal due to the lack of receptor degradation. It should be noted that although not shown, both the NGF and mutated EGF receptor models do include the PI3K-Akt pathway.