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19.4

Cellular Communication, Signalling Cascades, Metabolism,

Shannon Entropy

Communication in prokaryotes usually takes place via two-component systems, which

enables direct control (sensor activates responder, which then immediately initiates tran­

scription – thus responding quickly to an external stimulus). The situation is much more

complex in eukaryotes: Here it is mostly indirect and connected with intracellular com­

munication, e.g. via glucocorticoids and second messengers. Often there is also combina­

torial regulation via complex signalling cascades. To understand this, it is advantageous to

take a closer look at the RNA, DNA and protein networks.

Topological and Dynamic Modelling of Regulatory Networks

Protein–protein interactions (PPI) play an important role in the organism. One example is

signaling cascades, in which different proteins interact with each other (e.g. activate one

after the other) and typically regulate or amplify cellular signals. In addition to pairwise

interactions (number of possible interactions [n² − n]/2), there are of course also com­

plexes (number of possible complexes is 2ⁿ) between proteins, so that a large number of

possible PPIs exist, which makes it difficult to detect all interaction partners experimen­

tally or to predict them bioinformatically. In some cases, there are also tissue-specific

interactions.

How Do I Find and Analyse Protein Interactions and Networks?

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19.4  Cellular Communication, Signalling Cascades, Metabolism, Shannon Entropy