INFORMATION AND INACTIVATION OF 

 BIOLOGICAL MATERIAL* 



Harold J. Morowitz 



Department of Biophysics, Yale University, New Haven, Connecticut 



Abstract — An analysis of target theory has been carried out in terms of the language of in- 

 formation theory. Certain results suggest that radiation and thermal inactivation experiments 

 can be used to set limits on the values of information content of biological structures. A group 

 of such limits has been discussed, as well as a suggestion for using 'radioactive suicide' experi- 

 ments to evaluate information content. 



Information theory provides a discipline for quantifying order and specificity 

 in biological structures. Ionizing radiation and heat provide more or less 

 random methods of disordering biological structures. Therefore, we may 

 anticipate that infonnation theory and studies of the biological effects of heat 

 and ionizing radiation may in some way complement each other. In particular, 

 if we can make some quantitative statements about the amount of disordering 

 necessary for loss of biological function, we are then able to say something 

 about how much order is involved in specifying the system. 



The concept of target volume has an analogue in the representation of a 

 structure in terms of a series of symbols. If inactivation curves are exponential 

 and the target volume is less than the volume of the structure, we may conclude 

 that part of the structure (the critical target) has an information density higher 

 than the rest of the structure. That is, a subset of syinbols in the array require 

 much closer specification than the rest of the array. If no energy is transferred 

 and there are b symbols in the subset, the target volume will be bVjM, where V 

 is the total volume of the structure and M is the total number of symbols of 

 equal volume needed to specify the structure. If there is energy transfer with 

 high efficiency over g atoms, the volume will be of the order of bg^VjM, 

 assuming no overlap of partial volumes. 



In this paper we shall be concerned with those biological materials that 

 can be dried, taken to low temperatures and then returned to a functional 

 state without appreciable loss of activity. This class of materials includes 

 enzymes, viruses, spores, and transforming principle. In these entities we 

 may conclude that the information is contained in the structure. Several 

 methods have been used to evaluate the information content of these resting 

 systems. 



We shall outline briefly two methods that have been used to evaluate the 

 infonnation content of biological materials. In both methods it is assumed 

 that the atomic composition and volume are known. The volume may then 

 be divided into a number of elementary atomic volumes. To specify the 



* Supported by a Research Grant from the John A. Hartford Foundation. 



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