Non-genetic Biological Information Mechanisms

NON-GENETIC BIOLOGICAL INFORMATION MECHANISMS WINSTON SALSER* I. The Problem How the cell produces an exact replica ofitselfis one ofthe basic questions that biological research is trying to answer today. At present, the nucleic acids, and especially deoxyribonucleic acid, DNA, are the center of attention. DNA has been described by some people as a sort ofcarrier ofthe blueprint ofthe cell. This school ofthought seems to believe that the chromosomal complement ofthe cell, with its DNA, is all that is needed for the transference ofinformation from one generation ofcells to the next. This implies that the material ofthe nucleus contains all the information describing the structure ofthe cell. if the DNA of the cell does contain all of the information essential for the production ofa new cell, then all the tangled skein ofphenomena associated with cell metabolism and replication must be directly related to this one substance. Then we need only to determine how DNA replicates and how it expresses its information in order to understand how a cell produces an exact replica ofitself. This implication is well understood because a greatnumber ofresearch projectsattackthe problem ofcellreplication from the standpoint ofDNA. Many discussions in the literature have been devoted to demonstrating that everything goes back ultimately to a primary action ofDNA upon its environment, but oftenall that isactually shown is that the expression ofa given cell characteristic can be altered by nuclear genetic factors. That these are not the same thing is clearly indi- * Present address: in care ofCommittee on Biophysics, University ofChicago. My interests in this subject were stimulated during a research assistantship under Dr. Barry Commoner, Chairman, Committee oh Molecular Biology at Washington University. 177 cated by the behavior of many entities that are commonly designated intracellular parasites, such as symbiotic Chlorella of Paramecium and Stentor, which can clearly be demonstrated to be under some degree of nuclear control. On the other hand, ifthe DNA ofthe cell does not have a monopoly on the storage of the information essential for the production of a new cell, we will not be able to expect our increasing knowledge ofDNA to supply us with more than a partial understanding of the process of cell replication. In such a case an important step toward an ultimate understanding ofcell replication might be a search for other explanations ofinformation storage and expression which would complement the action of DNA within the cell. As a basis for further discussion ofthis problem it is helpful to examine a term which is usedfrequently—"information." In the language ofthermodynamics , "information content" is equated with negative entropy, and lack of information is defined as complete randomness of position and velocity ofthe particles ofa system, i.e., maximum entropy. Therefore, a system which contains a large amount of information will be a highly ordered system. The information ofthis system will describe its order. The cell is such a highly ordered system, and the information which it contains describes its structure. The hereditary information ofthe cell is not a complete description of the structure ofthe cell. Structure at a level which is easily disturbed by random kinetic energies, for instance, is obviously not fully described by the hereditary information of the cell. The hereditary information puts limits upon the structure, variation within those limits being determined by both random and non-random environmental influences. Thus, we see that the hereditary information ofthe cell differs from the total information of the cell, which can be rigorously defined in terms of negative entropy. Weneed to define hereditaryinformation, especially since it is the part ofthe cell's information which is ofmost interest to the biologist. It seems most useful to use an operational definition: Hereditary information includes all information necessary for the production of a new cell. We have defined information in terms ofa product, or an effect. This approach has some implications which are not immediately apparent. The presence ofhereditary information is indicated only by its expression in some way. Our only proof that a cell contains the information 178 Winston Salser · Non-genetic Information Perspectives in Biology and Medicine · Winter 1961 necessary for the creation ofanother cell, for instance, is observation ofthe process ofcell division. Adverse conditions, such as the presence of chemicals which...