My work with others of last three years is outlined in this seminar, by means of a brief description of three main approaches to model biological systems by computational methods. MP systems are realized by means of algebraic and algorithmic procedures applied to a symbolic representation of biochemical systems. They model metabolic dynamics quantitatively, meaning that a given temporal dynamics may be reproduced by an MP grammar, which is regulated by state functions. MP systems originate from membrane computing. In this framework, a P model is introduced as a non-deterministic qualitative model of a specific cellular dynamics. A few results about algorithmic models of DNA computing and some research in progress conclude the talk.