Team:Peking/test
What will you do if you could reprogram cells and design there life processes?
A periodic drug delivery to precise drug release in sequential order, appropriate time?
An automatic cell factory where all biosynthetic procedures in one fermentation tank?
Cells that can survive in harsh environements by making complex calculations about their surroundings going where no cells have gone before?
Why sequential logic?
Cells are responsive to a myriad signals under most conditions. Upon re-ceiving this cornucopia of signals, i.e. inputs from the external and internal environment, cells must adjust their own internal mechanisms in response in order to survive. This adjustment depends not only on processing a combi-nation of current environmental signal inputs , but also on determining the cell’s current state, which is a result of a series of past inputs. Habituation and hypersensitivity are good examples.
In digital cir-cuit theory, this operating mode is known as sequential logic. Sequential logic is a type of logic in which output is a function of the present value of inputs and the system’s internal state.
The field of synthetic biology aims to design biological systems to perform tasks to better understand analogous natural systems and to devel-op direct applications for research and medicine. Nowadays, a wide variety of tasks can be performed by synthetically engineered genetic circuits, most-ly constructed using combinational logic. The output of combinational logic (also referred to as time-independent logic) is a function of the present input only. In contrast to sequential logic, it has no internal state as an influence of the history of inputs. Without a memory of state, it is difficult to perform functions in a specific order, which has limited the widespread implementa-tion of such systems.
The ability of sequential logic circuits to store modest amounts of information within living systems and to act upon them would enable new approaches to the study and control of biological processes . More functions could be accomplished with a memory module embedded within the circuit. Once the memory system is able to scale up to more states, a cell can be designed to do work that is more complex. In other words, we can reach a new dimensionality in design-ing synthetic life – time.
What we did
This year, the Peking iGEM team is attempting to develop a frame of bio-logical sequential circuits that are programmable. The envisioned circuit is capable of both storing states in DNA and automatically running a series of instructions in a specific order. More specifically, the sequential logic (or a real-state machine) that consists of a clock (trigger signal), flip flop (re-membering device) and control unit (functional part) in bacteria. The clock is an oscillator with a repeated signal cycle that is utilized like a metro-nome to trigger actions of sequential logic circuits. Flip-flop is a memory device that can remember a state. Paired with a clock signal, it can realize state transition. The control unit is a functional part which can convert a signal from flip-flop into complex functions. With such a design, historical events are recorded and influence current cell behavior.
This work tries to point the way toward building large computational sys-tems from modular biological parts—basic sequential computing devices in living cells—and ultimately, programming complex biological functions. Computers have thus become "alive". A unicellular organism itself cannot pack much computational power, but considered as a modular building block, its potential is impressive.
