Multi Cellular Glossary

• Apoptosis -- the technical term for Programmed Cell Death. It is absolutely vital for the development of multicellular organisms, for the everyday maintenance of the organism, and for defense against viruses, DNA damage, etc. It shows up in computing too -- both in hardware and software. For a good tutorial on the biological process, see http://www.irishscientis ... xsl=insight3.xsl

• Biofilm -- A cooperative community of single-cell organisms, usually prokarotes (backteria). The community builds an extracellular matrix of slime or fibrous material. Signals (messages) between them can trigger "quorum" behavior when the community gets large enough. See http://en.wikipedia.org/wiki/Quorum_sensing for more detail. Biofilms can be thought of as "training wheels" for multicellular life in that the individual cells can still live a free-standing life if needed and they have separate complements of DNA. So the cells in a particular contiguous biofilm are not "commited" to a multicellular life and a common evolutionary fate in the way the cells in a true multicellular organism are.

• Conjugation -- A process whereby bacteria exchange DNA. One of the pair creates a hollow filament that joins the two bacteria. Then DNA is passed through this filament. See http://en.wikipedia.org/ ... rial_conjugation

• Eukaryote -- The category of cells that contain a membrane-enclosed nucleus. The simpler (and older) bacteria are called Prokaryotes; they lack a nucleus. The cell's nucleus contains most of the DNA, the molecular machinery that copies the DNA, and the complex mechanisms that determine which genes are to be expressed (i.e., cause proteins to be manufactured). So eukarote cells are more complex and can be much more finely controlled than prokaryotes. See http://en.wikipedia.org/wiki/Eukaryote for more.

• Metazoan -- A multicellular animals having cells differentiated into tissues and organs and usually a digestive cavity and nervous system. Note: for the purposes of the multicellular computing discussion, everything said about multicellular animals applies equally well to plants. Consider the term Metazoan here to be essentially equivalent to Multicellular Organism.

• Prokaryote -- Single-cell organisms that lack a nucleus and most other complex organelles. See http://en.wikipedia.org/wiki/Prokaryote for more.

• Protein domain -- The common belief is that proteins have a single function. In fact, what we learned in high school biology was that each gene coded for one protein which has one function. But especially in eukaryotes, genes may have multiple sub-sections that code for different more-or-less independent portions of the final protein. These portions are called domains. They often have quite different functional roles. A multi-domain protein may attach to some other protein using one domain and carry out some catalytic function using a separate domain. (See http://en.wikipedia.org/ ... tructural_domain for more) The point of bringing up this issue here is that, when considered as a polymorphic message, a multi-domain protein amounts to a multi-part message that, in effect, orchestrates complex behavior in the receiver.

• Stigmergy -- Stigmergy is a method of communication in emergent systems in which the individual parts of the system communicate with one another indirectly by modifying their local environment. Familiar examples in the biological world include termite nests and ant colonies where the behavior of the insects is guided by chemical cues (pheromones) that are deposited in the mound or tunnels by some of the insects, linger there, and cause other insects that arrive later to modify their behavior accordingly. Familiar examples in computing include open-source code repositories -- code that is deposited by one programmer affects the subsequent behavior of other participating programmers.