# DNA Computing: Concepts for Medical Applications
## 5 Discussion
It is worth noting that queuing systems can be combined to form queuing networks [46], which enable complex systems based on queues to be designed. Biomolecular implementation consists of the appropriate encodingof all elements of the system, where the queue is the hardest element to implement. It should be noted that the idea of biomolecular implementation of a queue is provided in the present paper. For instance, in every queuing system, one can use one type IIB restriction endonuclease and combine it with others so that they form a queuing network. Theoretical studies on biomolecular computers may provide practical solutions. Such new methods and models may have numerous medical applications, complementing conventional therapies and laboratory diagnostics. Early research on biomolecular computers focused on human-operated, laboratory-scale computers for solving complex computational problems. More recently, simple, autonomous and programmable molecular computers have been presented in which the input and output information can be given in a molecular form. Such computers, using biological molecules as input and biologically active molecules as output, could create a system for the \"logical\" control of biological processes. An autonomous biomolecular computer is proposed, which, at least in vitro, logically analyzes mRNA levels and responds by producing a molecule capable of affecting gene expression levels. This approach can be applied in vivo for biochemical sensing, genetic engineering, and even medical diagnosis and treatment. A good example of the use of biomolecular computers is the concept of cancer diagnostics and cancer treatment based on silencing a cancer gene expression [47]. With this approach in mind, [PERSON]'s team developed a method for the activation of biomolecular software for cases where the reaction mixture contains typical neoplastic mRNA. For that purpose, they used a simple biomolecular computer, developed in a similar way as in their previous experiments [3; 4]: it was built of software (in the form of double-stranded DNA) and hardware (in the form of the _F_okl restriction enzyme), which could only assume one of two states--\"yes\" or \"no\". If \"cancer mRNA\" was present, then the biomolecular computer switched to the \"yes\" state; otherwise, it was in the \"no\" state. When all the sought for cancer features in the form of mRNA were present in the reaction mixture, then the biomolecular computer completed its operation and yielded the diagnosis of \"yes\", confirming the presence of cancer genes. Then, it released a drug capable of silencing the cancer gene expression. A part of that approach was also the proposed new concept of designing the input word, which enabled the release of the drug after the final cutting of the double-stranded DNA encoding the symbols of the biomolecular computer. Another interesting application of DNA computing is the general concept of designing reconfigurable DNA nanovaults capable of controlling interactions between the enzymes [48]. Of particular interest seem to be issues involving DNA sequencing, where Sanger's sequencing remains the basic method [49]. Interestingly, one of the methods of studying sequencing is based on the use of class IIS restriction enzymes [33; 50], and another, similar approach to sequencing is used as well [34; 51]. The proposed concept, of which DNA sequencing is the main aim, is based on reading DNA by the restriction enzymes. It is worth noting that the idea of sequencing with the use of the restriction enzymes was shown before the first practical experiment, i.e., implementing biomolecular computers with a single restriction enzyme [3]. It is particularly interesting to study the feasibility of sequencing in the aspect of programming and using biomolecular computers, because the two approaches complement each other. It seems that comprehensive studies on sequencing with the use of biomolecular computers will yield numerous practical solutions in the field of sequencing.