small 30S subunit
Mostly multicellular, with cell differentiation
Source: After Klipp et al. (2005).
Source: After Klipp et al. (2005).
only certain ones will be expressed at a given time or for a specific cell type. Some genes which perform basic functions are always required; these are constitutive or housekeeping genes. Others are expressed only under certain conditions (Klipp et al., 2005, pp. 45-47).
Openness in the scenario just given is particularly pronounced at the nuclear and cuto-plasmic boundaries, but in fact is expressed all along the way as intracellular structures receive, process, and pass along the various intermediary products in protein synthesis. Is the openness sufficient to ensure uptake of oxygen and nutrients needed for protein synthesis? Matter needed for the biochemistry is proportional to the volume (we presume that the cell is a sphere where d is cell diameter):
The transport from the surface to the cell takes place by a fast active transport and the concentration at the surface is, therefore, 0. The area of the sphere is nd2. The flux of matter toward the cell is considered constant, which implies that the concentration gradient will decrease with the distance from the cell in the exponent 2:
where r is the distance from the center of the cell (radius). The concentration is 0 at the surface of the cell, i.e. r = d/2. The concentration at the distance r from the center of the cell Cr can be found after differentiation of Equation 2.27 to be:
The diffusion rate, corresponding to the uptake rate is a diffusion coefficient (D)X the concentration gradient (dC/d r = Cd/2r2 or at the surface = 2C/d) X the openness = area = nd2, or therefore 2ndDC, where D is the diffusion coefficient and C the concentration in the environment. The uptake rate relative to the need, denoted UR/N, is found as:
where f is the need per unit of time and volume. The relative uptake rate will be four times smaller, if the diameter is doubled. Relatively small cell sizes are necessary to obtain a sufficient relative uptake rate.This equation demonstrates the importance of the cell size and explains, therefore, indirectly the hierarchical structure, because small cells are the prerequisite for a sufficient supply of nutrients, although there are many additional explanations.
2.8 WHAT ABOUT THE ENVIRONMENT?
Openness is a requisite for moving substance across boundaries, and boundaries imply an inside-outside dichotomy. That is, in departure from thermodynamic equilibrium energy and matter move from outside to inside and dissipation signifies movement in the reverse direction, from interiors to exteriors.
The term "environment" has appeared 44 times previously in this chapter, in a book on ecology, the biological science of environment, and yet we have not once anywhere done anything explicitly with this concept except take it for granted as a reference source and sink from which some older more or less accepted thermodynamics, without its modern challenges, proceeds to operate in the organization of ecosystems. We use the concept of environment, but have not attempted to define it scientifically or explore it in any deep way. There is little in theoretical ecology that elaborates it in substantive scientific terms. It is just a convenient category of "surroundings" that openness requires—some place to derive inputs and exhaust outputs.
Particle scales aside, it is relevant in the context of openness to ask the hard question— "What is environment?" We look around the room or outside the window and see what everyone agrees is "environment." Seeing is only part of it, however; there is also touching and smelling, etc. In other words there are sensory stimuli involved. What about these? Our household pets and the plants in the garden that began this chapter have considerably different sensory apparatus from us. Does that mean environment is relative, something that can only be defined by perception? Or are certain aspects of it accessed differently by different open systems? It is clear from the perspective of reality as a collection of physics' particles, and from mass-energy conservation, that what comes to me at a given moment as visual, auditory, tactile, etc. stimuli cannot also come to you or your dog or plant. At this level it has to be acknowledged that there is a certain uniqueness that attaches to the "environments" of particular open-system receivers of sense-data. Not only is this true for sensory stimuli, but also is true for the masses of matter that enter our bodies as food, and exit as biodegradable products useful as food for other organisms. So environment, it would seem, courses in and out of open systems, and the ultimate particle uniqueness of the substance and signals both seem to confer a central place on the open system as the focal arbiter of environment. Afferent input environments coming from the past are originated the moment a unit of high-quality energy or matter crosses the boundary of a receiving open system. This increases the exergy and lowers the entropy of the receiving system. Reciprocally, efferent environments that unfold with the future are founded the moment a unit of energy or matter exits the said open system. This dualistic concept of environment is operationalized in the mathematical theory of environs (Patten, 1978, 1982), about which now numerous papers have been published describing the properties of such structures. The dualism is central, and so is the unity of the focal entity-environ triad. Environments and the things with which they are associated can never be separated in environ theory—they are a unit of nature, however intractable, but sometimes with surprising holistic properties.
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