UNIT 7 Molecular Structure of Biological Systems. Part 1

Two kinds of physical behavior meet at the molecular level of biological structures: on the one hand, there are the characteristic properties of microphysical processes, based on the individual behavior of single small particles like atoms, molecules or supramolecular structures. These processes are mostly stochastic. On the other hand, there are reactions which resemble "macrophysical" properties, the kind of behavior of "large" bodies. The "macrophysics" is ruled by the laws of classical physics, for example classical mechanics. Our daily experiences with macrophysical systems teach us that their behavior is generally deterministic.

To explain this difference, let us consider a simple mechanical wheelwork. The knowledge of its design and construction allows a precise prediction of the behavior of the system. This prediction is based on the laws of classical mechanics. In contrast to this, a chemical reaction with a small number of molecules in a homogeneous phase depends on stochastic collisions of the individual molecules with each other. Since this process is stochastic, it is only predictable in a statistical way.

This stochastic behavior of molecular systems can be transformed into a deterministic one, if the number of participating stochastic events is large, or if the degrees of freedom of the single reactions are extremely limited. The increase of stochastic events can be realized either by an increasing number of participating molecules, by enlarging the volume for example, where the reaction takes place, or by an increase of the time interval of observation. This consideration indicates an interesting interplay between volume, time constants, and reliability of a biochemical reaction.

Define the following words using a dictionary

Stochastic, supramolecular, quantum, controversy, homogenous, wheelwork, interplay

Complete the sentences

1. It is the intention of this section…
2. The leading idea of this section…
3. On the one hand, there are the characteristic properties of microphysical processes,...
4. On the other hand, there are reactions…
5. The knowledge of mechanical wheelwork design and construction allows…
6. Our daily experiences with macrophysical systems teach us that…
7. Since this process is stochastic,…
8. The increase of stochastic events can be realized…