  Protein molecules in cells are synthesized by macromolecular machines called
ribosomes. According to recent experimental data, we reduce the complexity of
the ribosome and propose a model to express its activity in six main states.
Using our model, we study the translation rate in different biological relevant
situations in the presence of external force, and translation through the RNA
double stranded region in the absence or presence of the external force. In the
present study, we give a quantitative theory for translation rate and show that
the ribosome behaves more like a Brownian Ratchet motor. Our findings could
shed some light on understanding behaviors of the ribosome in biological
conditions.
