communication

Cells, whether unicellular organisms or cells within multicellular organisms, respond to signals within their environment. Such signals include mechanical stimuli (light, sound) or chemicals. The origin of chemical stimuli may be the cell itself (autocrine), adjacent cells (paracrine), the plasma membrane of adjacent cells (contact inhibition), or distant cells (endocrine).

Neurotransmission involves communication between or to cells of the nervous system, and incorporates interaction between neurotransmitters and specific receptor proteins. Cytokines mediate paracrine stimulation, and hormones mediate endocrine stimulation.

Cellular responses to signalling molecules include alterations in gene expression (transcription), alteration of electrophysiological charge, and alteration of metabolic activity of the cell.

Intracellular interactions in prokaryotes
Four kinds of cell interactions can be distinguished:
1) Transfer of a chemical signal from one cell to another via signaling molecules such as neurotransmitters and hormones.
2) Signaling by direct physical contact between two cell bodies, which may involve their surfaces or cell appendages, such as fibrils, pili, or flagella. Direct physical contact is often involved in cell swarming.
3) Syntrophic metabolism. Schink (Syntrophism Among Prokaryotes).
4) Gene transfer from one cell to another – conjugation, transduction, transformation , and endosymbiotic gene transfer.

Eubacterial gene transfer interactions are widespread. Transfer within the Archaea has recently been observed, and their genetics is being developed (Stedman et al., 1999; Whitman et al., 1999). Prokaryotes have three mechanisms for unidirectional gene transfer from a donor to a recipient. These mechanisms are transformation in which naked DNA from the donor is taken up by the recipient, generalized transduction in which a phage has packaged a head-full of donor DNA and injects that DNA into the recipient, and conjugation in which a specialized apparatus in the donor transfers a long DNA segment directly into a conjugating recipient.

• A • adhesion • C • cell membranes • cellular adhesion molecules • cellular signal transduction • centrioles • chemotaxis • chloroplast • cilia & flagella • communication • concentration gradients • cytokine receptors • cytoplasm • cytoskeleton • E • energy transducers • endoplasmic reticulum • endosomes • exosome • F • flagella & cilia • G • Golgi apparatus • GPCRs • H • hormones • I • ion channels • L • lysosome • M • meiosis • microtubules • mitosis • mitochondrion • N • Nitric Oxide • neurotransmission • neuronal interconnections • nuclear membrane • nuclear pore • P • pinocytosis • proteasome • pumps • R • receptor proteins • receptor-mediated endocytosis • S • second messengers • signaling gradients • signal transduction • spindle • structure • T • transport • two-component systems • V • vacuole • vesicle •