Chapter 1.  Introduction

Table of Contents

What is MesoRD?
An introductory Example
Where we go from here
System Requirements
Mission Statement
Project Status
What is new in MesoRD 1.1
What is new in MesoRD 1.0
What is new in MesoRD 0.3
Known Bugs
Citing use of MesoRD

What is MesoRD?

MesoRD is a tool for stochastic and deterministic simulation of chemical reactions and diffusion in 3D, and planar 2D spaces[1].

The description of the system that you want to simulate is written in the SBML file format [Finney and Hucka 2003] . The SBML file contains all information about the species, reactions, reactions rates, compartment geometries, diffusion constants etc. In addition to the SBML file, MesoRD will require information about how the simulation should be executed, such as spatial discretisation of the reaction volume, duration of the simulation, visualisation, output options, and for deterministic simulations, also choice of integration method. These parameters are given through the MesoRD user interface. The output files from MesoRD are intended for external data analysis and visualisation packages, for instance the freely distributed MesoRD Matlab toolbox available from the MesoRD website.

In both the deterministic and the stochastic mode of simulation the reaction volume is discretised into a large number of small subvolumes and the state of the system is given by the number of molecules per subvolume. In the stochastic simulation the number of molecules per subvolume are discrete. Furthermore, the reaction and diffusion events that change the number of molecules are probabilistic, in the sense that the next event in the systems is sampled from a distribution function. In the deterministic simulation the state is assumed to be a continuous variable and the change in the number of molecules per time unit is given by the average change as defined from the stochastic model. A more detailed description of the differences between the stochastic and deterministic way of modelling is given in the theory section Chapter 6, Rates and state changes in MesoRD .

An introductory Example

One example of a system that can be easily modelled in MesoRD is the one illustrated in the figure below. B-molecules are synthesised by a membrane bound A-molecule. The B-molecules diffuse into the cytoplasm and are degraded or modified in a first order reaction. Some B-molecules reaches an intracellular compartment, where they dimerise into a D molecule, which also can be degraded.

Figure 1.1.  Example of a three compartment geometry.

Example of a three compartment geometry.

The system has a non-trivial geometry, it is non-homogeneous, and it may have some interesting stochastic properties. It is therefore suitable for simulation in MesoRD. How this model is described in SBML for MesoRD is described further in Chapter 7, Tutorial .

Where we go from here

The rest of the introduction includes the section called “ Mission Statement ”, the section called “ System Requirements ”, the section called “ Project Status ”, the section called “ Citing use of MesoRD, and the section called “ Funding ”, but maybe you want to start making models.

Constructing models for MesoRD is mainly a question about writing, or generating as it may be, valid SBML [Hucka et al 2008] files. However, there are some special considerations one has to keep in mind when working with MesoRD.

All this assumes that MesoRD has been successfully installed. Installation is covered in Chapter 2, Installation . The impatient may as well skip ahead to any of the above chapters.