Signal Transduction - Environmental Stimuli

Environmental Stimuli

With single-celled organisms, the variety of signal transduction processes influence its reaction to its environment. With multicellular organisms, numerous processes are required for coordinating individual cells to support the organism as a whole; the complexity of these processes tend to increase with the complexity of the organism. Sensing of environments at the cellular level relies on signal transduction; many disease processes, such as diabetes and heart disease arise from defects in these pathways, highlighting the importance of this process in biology and medicine.

Various environmental stimuli exist that initiate signal transmission processes in multicellular organisms; examples include photons hitting cells in the retina of the eye, and odorants binding to odorant receptors in the nasal epithelium. Certain microbial molecules, such as viral nucleotides and protein antigens, can elicit an immune system response against invading pathogens mediated by signal transduction processes. This may occur independent of signal transduction stimulation by other molecules, as is the case for the toll-like receptor. It may occur with help from stimulatory molecules located at the cell surface of other cells, as with T-cell receptor signaling. Single-celled organisms may respond to environmental stimuli through the activation of signal transduction pathways. For example, slime molds secrete cyclic adenosine monophosphate upon starvation, stimulating individual cells in the immediate environment to aggregate, and yeast cells use mating factors to determine the mating types of other cells and to participate in sexual reproduction.