Stochastic simulation of genetic networks based on
models in the stochastic pi calculus is a promising 
recent approach. This talk presents an extensible
 model of  the central mechanisms  of gene expression 
i.e. transcription and translation, for the prototypical
case  of bacteria.  We reach extensibility through
an object-oriented programming style in the pi calculus,
and a module system. We use  multi-profile objects 
with inheritance, that are compiled into the stochastic
pi calculus extended by  pattern  guarded choices. 
We illustrate the coverage of our model in a
simulation case study that demonstrates  translational
bursting in bacterial gene expression.