In the absence of tryptophan, what happens to the genes within the trp operon? a) the regulator without tryptophan-binding prevents the genes from being transcribed. b) the regulator falls off the operator and structural genes get transcribed. c) lack of tryptophan increases the level of camp high, which leads to activation of cap protein and gene expression. d) the active repressor binds to the operator and genes do not get transcribed. e) the active activator binds to the operator and transcription of structural gene takes place.