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“chaotic”. Only by measuring the state of the system with very high accuracy can I accu­

rately describe how my system is evolving for short periods of time. But any error grows

over time. And in “chaotic” systems it doubles within a short time, so that already after ten

such time units the error is more than 1000 times larger after these ten doubling steps (2 to

the power of 10 = 1024). For this reason, the behaviour of such systems over longer peri­

ods of time cannot be described exactly. On the other hand, it is precisely the negative

feedbacks that keep the system within fixed limits (climate in the case of the weather at a

particular location, health in humans). Only if strong positive feedbacks transform the

respective system state, it is possible that it changes rapidly (tipping point) and one then

suddenly has a new state (climate change or in humans a disease). The sudden system

change when crossing tipping points was considered mathematically by Rene Thom

(catastrophe theory, because systems then change catastrophically and rapidly).

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9.1

The main effect of a drug is often the blocking of a receptor, i.e. the blocking of signal

transduction via this receptor molecule. In Sect. 5.1 we gave the example of receptors in

the cardiac muscle cell, which then lead to heart failure via phosphorylation of Erk kinase.

Ideally, that would then be all the effects of the drug. Would we then also see this in the

gene expression experiment, i.e. only a down-regulation of the messenger RNA for the

ß-adrenergic receptor, if, for example, we carefully creep in a beta-blocker against the

increased blood pressure and the heart failure? Interestingly, we wouldn’t see that exactly

because the receptor is made (“expressed”) via the mRNA, just as it is without the drug

administration. If this were not the case, the drug could not bind to it at all. If the receptor

does not transmit its signal, the heart has less work to do and the patient feels better. This

is the intended and proven heart-protecting effect of beta-blockers. This can only be done

by carefully increasing the dosage. Unfortunately, beta-blockers do lead to an improve­

ment in symptoms, but not to a prolongation of life. This is due to the fact that the cause,

the ageing heart, is not really combated without future methods such as stem cells for new

cardiomyocytes. This is exactly why we are doing intensive research on stem cells in our

9.1  Complex Systems and Their Behaviour