![]() ![]() If the input signal is a periodic clock signal, then a clock pulse signal can be synthesized. A pulse generator generates an instantaneous stimulating signal and then resets to the original state by using time difference between the input and the corresponding delayed signals. By cascading odd number of repressor genes in the cycle chain, a genetic oscillator can be synthesized to generate a stable oscillation signal in the protein response and applied in the control of dosage of drugs, or regarded as a synchronous mechanism for cell-cell communication. Toggle switch applies two repressor genes repressing each other to cause bi-stable phenomenon, like as a memory device. ![]() The former twos are based on protein-protein interaction without any external input to control their behaviors. ![]() Inspired by electronic circuits, several synthetic genetic circuits have recently been created, such as toggle switch, genetic oscillator, pulse generator, genetic counter, logic evaluator, sensor, filter, and cell-cell communicator. In addition, there are still potential applications in biofuels, biotechnology, bioremediation, and bioenergy remained to be developed. For drug development and disease treatment, synthetic biology brings a useful and rapid direction through inserting the designed genetic circuits into the host cells to improve or modify the disease state of organisms. By using mathematical models to capture the quantitative and qualitative characteristics of biological systems, the customized genetic circuits with specific functions can be designed from the system perspective. Based on a bottom-up approach, more complicated bio-computing modules can be expected to perform more complex functions via integrating a variety of biological devices, like very-large-scale integration circuits in electronics. Analogous to an electronic circuit, the synthetic genetic circuit also includes some standard biological components to assemble the biochemical process of living organisms and achieve specific functionality. Synthetic biology is an emerging interdisciplinary research field, which concentrates on understanding the behaviors of biological system from system-level as well as creating an artificial genetic circuit based on the principles of systems biology, mathematics and engineering. Based on analogous implement of digital sequential logic circuits, genetic sequential logic circuits can be constructed by the proposed approach to generate various clock signals from an oscillation signal. ConclusionsĪ cascaded genetic logic circuit generating clock pulse signals is proposed. The function acts like a frequency divider in electronic circuits which plays a key role in the sequential logic circuit with specific operational frequency. A synchronous genetic counter circuit based on the topology of the digital sequential logic circuit is triggered by the clock pulse to synthesize the clock signal with an inverse multiple frequency to the genetic oscillator. By controlling the threshold level of the genetic buffer, a genetic clock pulse signal with its frequency consistent to the genetic oscillator is synthesized. ![]() An analogous electronic waveform-shaping circuit is constructed by a series of genetic buffers to shape logic high/low levels of an oscillation input in a basic sinusoidal cycle and generate a pulse-width-modulated (PWM) output with various duty cycles. This paper presents a genetic sequential logic circuit with a clock pulse generator based on a synthesized genetic oscillator, which generates a consecutive clock signal whose frequency is an inverse integer multiple to that of the genetic oscillator. How to synthesize a specific clock signal is a preliminary but a necessary step to further development of a biological computer in the future. For the different cell types, it is supplied with various rhythmic frequencies. Rhythmic clock widely occurs in biological systems which controls several aspects of cell physiology. ![]()
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