In any biological system, for example, bacteria, cultured human stem cells, or cells interacting in tissues, a variety of networks and pathways are responsible for the basic functioning and robustness of the system. Examples of networks and pathways are:
| Metabolic pathways, for example, the famous Krebs cycle (Noble prize awarded in 1953). The Krebs cycle, also known as the citric acid cycle, is central to the chemical processing of carbohydrates, fats, and proteins to produce energy. The image gives a glimpse of the complexity of a metabolic pathway. | ![]() |
| Cell signalling pathways are part of a complex system of communication through which cells perceive and respond to their environment. | ![]() |
| Heat shock response, the process whereby cells counter the effect of heat, which causes protein unfolding and malfunction. | ![]() |
| The human immune system, a network of proteins, cells, organs, and tissues that interact in intricate ways to maintain good health. | |
![]() The immune system in action |
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Because biological networks are complicated regulatory systems, one expects that feedback will play an important role and that there will be similarities with man-made control systems. The goal in applying methods from systems and control theory to biological systems, now known as systems biology, is to gain a deeper understanding of the design principles of biological organization. This knowledge is being applied extensively in developing biotechnology, for example,