Examples

Figure 14.1 depicts gene expression and its role in catalyzing certain chemical reaction in the cell. The proB gene is being expressed into the gamma-glutamyl-kinase protein, which catalyzes a reaction involving glutamate and ATP, which produces gamma-glutamyl-phosphate and ADP compounds.

  

Figure 14.1: An example for the role of gene expression in catalyzing chemical reactions.

This gene expression is a part of a simple metabolic pathway, involving a chain of generated proteins, which is shown on figure 14.2. One of the final products of the chain, proline, inhibits the initial reaction, which has started the whole process. This "feedback inhibition" pattern is highly typical to genetic networks, and serves to regulate the process execution rate.

  

Figure 14.2: An example of an metabolic pathway: Proline biosynthesis.

The following two figures show a more complex gene network, describing Methionine biosynthesis in E-coli. The second figure is a shortcut representation of the pathway, with most nodes omitted, but it can give a better idea on overall topology.

  

Figure 14.3: Methionine biosynthesis network in E-coli.

  

Figure 14.4: Shortcut representation of the biosynthesis pathway presented in Figure 14.3

The last example is that of signal transduction - complex cellular process initiated by signaling protein arrived from outside of a cell. This process eventually affects gene expression in the cytoplasm and inside the nucleus.

  

Figure 14.5: A gene network that performs signal transduction from outside the cell into the nucleus.