In recent paper{\it  [Phys. Rev. E {\bf 83}, 042903 (2011)], a simple model for  the translation of messenger RNA  by ribosomes is provided, and the expression of translational ratio of protein is given. In this comments, varied methods to get this ratio are addressed. Depending on a different method of protein from mRNA to degradation rate \omega_p of protein, is obtained. The key point to get this ratio r is to get the translation rate \rm tl. In the study of Valleriani }{\it   is assumed to be the mean value of measured translation rate, i.e. the mean value of ratio of the translation number of protein to the lifetime of mRNA. However, in experiments different methods might be used to get \rm tl. Therefore, for the sake of future application of their model to more experimental data analysis, in this comment three methods to get the translation rate \rm tl, and consequently the translational ratio r, are provided. Based on one of the methods which might be employed in most of the experiments} , we find that , roughly speaking, this translational ratio decays exponentially with mRNA length in prokaryotic cell, and reciprocally with mRNA length in eukaryotic cells  .
In the recent paper of Valleriani{\it et al [Phys. Rev. E {\bf 83}, 042903 (2011)], a simple model for describing the translation of messenger RNA (mRNA) by ribosomes is presented, and an expression of the translational ratio r, defined as the ratio of translation rate \omega_{\rm tl of protein from mRNA to degradation rate \omega_p of protein, is obtained. The key point to get this ratio r is to get the translation rate \rm tl. In the study of Valleriani }{\it et al , \omega_{\rm tl is assumed to be the mean value of measured translation rate, i.e. the mean value of ratio of the translation number of protein to the lifetime of mRNA. However, in experiments different methods might be used to get \rm tl. Therefore, for the sake of future application of their model to more experimental data analysis, in this comment three methods to get the translation rate \rm tl, and consequently the translational ratio r, are provided. Based on one of the methods which might be employed in most of the experiments} , we find that the translational ratio r decays exponentially with the length of mRNA in prokaryotic cells, and decays reciprocally with the length of mRNA in eukaryotic cells . This result is slight different from that obtained in Valleriani's study .
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