Complexity in Biological Signaling Systems

Abstract

Biological signaling pathways interact with one another to form complex networks. Complexity arises from the large number of components, many with isoforms that have partially overlapping functions; from the connections among components; and from the spatial relationship between components. The origins of the complex behavior of signaling networks and analytical approaches to deal with the emergent complexity are discussed here.Signaling in biological systems occurs at multiple levels. In its broad sense, one could use the term "signaling" to describe events ranging from interactions between single molecules to interactions between species in ecological systems. The aim here is to deal with complexity in signaling at a single level: intracellular signaling within a cell. We will outline how current and forthcoming tools in biochemistry, cell and molecular biology, and physiology, as well as theoretical analysis and simulation methods, may be used to study this complex system. In a general sense, the adjective "complex" describes a system or component that by design or function or both is difficult to understand and verify. In the past decade, analysis of complex systems (the field of complexity) has emerged as a distinct facet of mathematical and physical sciences. Understanding of biological systems may be enhanced by analysis of their complex nature. In physical systems, complexity is determined by such factors as the number of components and the intricacy of the interfaces between them, the number and intricacy of conditional branches, the degree of nesting, and the types of data structures. Biological signaling networks possess many of these attributes, as well as dynamic assembly, translocation, degradation, and channeling of chemical reactions. All of these activities occur simultaneously, and each component participates in several different activities.One approach to understanding complexity is to start with a conceptually simple view of signaling and add details that introduce new levels of complexity. As this process unfolds, it becomes clear where experimental data end and how progressively more difficult it becomes to understand the system as a whole in terms of the functional details of individual components. A Signaling WireThe simplest description of signaling may be in terms of elementary chemistry in a homogenous well-stirred cell where all molecules have equal access to each other. Here, the most upstream component of the signaling pathway interacts with an external source and

The biology and evolution of music: A comparative perspective

“…By complexity I mean that musical signals (like linguistic signals) are more complex than the various innate vocalization available in our species (groans, sobs, laughter and shouts). Although complexity can be measured and quantified in various ways (see, e.g., Homer & Selman, 2001;Shmulevich & Povel, 2000;Simon, 1972;Weng, Bhalla, & Iyengar, 1999), there is no single widely used metric applicable to all musics (Pressing, 1998), so it would be premature to specify any absolute threshold for ''complexity'' at present. Oddly, Hockett did not include complexity on his list of design features, although its necessity for language is implicit in his discussion.…”

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