Chemical signaling complexes

This section reviews the complex currents lobsters generate to eliminate metabolites and broadcast chemical signals and the return currents from which they obtain chemical signals and metabolic energy. Lobsters are examples of hard-shelled animals that store urine and feces, allowing them to be chemically "quiet" when necessary. 

Together, the two lobster-generated currents that can be measured around the animal s anterior end are complex and carefully controlled. They are ideally suited to carry urine, urine pheromones, and gill metabolites away from the lobster to specified directions. Simultaneously, the water displaced by these outgoing currents results in incoming currents with chemical signals from the environment that can be sampled by the antennular chemoreceptors. 

Zhang, M. and Wang, W. (2003) Organization of signaling complexes by PDZ-domain scaffold proteins. Accounts of Chemical Research, 36, 530-538. 

Because the chemical signals (semiochemicals) are normally produced in minute amounts and diluted in the environment with a complex mixture of chemical compounds derived from a myriad of sources, the olfactory system in insects evolved as a remarkably selective and sensitive system, which approaches the theoretical limit for a detector. For example, it has been estimated that the male silkworm moth is able to distinguish within 1 s 170 nerve impulses generated by the female silkworm moth s sex pheromone from 1700 spontaneous nervous impulses [ 1 ], thus, operating on a remarkably low S/N ratio ... 

Negative entropy is also expressed in the ordered three-dimensional structures of complex proteins, protein-nucleic acid complexes, molecular machines, biological membranes, and so on. Metabolism and chemical signaling too are highly and meticulously ordered processes. Use your brain to think about the brain the degree of order in the creation of trillions of connections among nerve cells that is required to allow us have that most amazing facility, consciousness. 

Chemical cues attract the sexes and modulate sexual behavior in many or most mammal species. Chemical signals also often reveal the quality and reproductive potential of individuals. In addition to chemical cues, multiple cues in different sensory modalities guide the complex reproductive behavior of mammals. 

Blockade of this important signal transduction pathway leads to impaired ability of neurons to respond to activation of membrane receptors for transmitters or other chemical signals. Another site of action of lithium may be GTP-binding proteins responsible for signal transduction initiated by formation of the agonist-receptor complex. 

Animal cells add a significant layer of complexity to the system due to their dependence on cell-matrix and cell-cell signaling pathways. Unicellular species such as bacteria and yeasts tend to grow and proliferate as fast as nutrients can be supplied. In fact, their growth rates are typically proportional to the amounts of nutrients available. By contrast, however, cells from multicellular organisms must develop mechanisms that include both nutrient supplies and signal pathways that control cell division. Thus, while nutrients are necessary for an animal cell to proliferate, the cell must receive stimulatory chemical signals from other, usually adjacent, cells. 

Laing, D.G. and Livermore, B.A. 1992. Perceptual analysis of complex chemical signals by humans. In Chemical Signals in Vertebrates VI (R.L. Doty and D. Muller-Schwartze, eds.) pp. 587-593. Plenum Press, New York. 

Effective colonization of a surface by bacteria can occur in a number of different stages and occurs at both the level of the individual cell and in multicellular populations and communities. Pragmatically, the time course of bacterial colonization from initial attachment to complex biofllm formation is also often short in comparison to the time course of settlement and metamorphosis for larvae of many invertebrates. Thus, bacterial colonization is broadly considered here to include directional swimming (e.g., the ability to approach a surface) (see also Chapter 12 in this volume), attachment, various kinds of surface motility, and biohlm formation. Chemical signals can affect all stages of this process for bacteria, although direct evidence is sparse for marine bacteria. 

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