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Team:BIOSINT Mexico/Sensor
From 2014.igem.org
Modular Sensor
Description
There has been an increasing necessity to implement new, efficient and inexpensive techniques for the identification of biological and chemical agents that contaminate the environment, one of the most developed strategies for solving this trouble is the use of biosensors. A reporter device must be an easily detectable mechanism for sensing a specific substance of interest, this reporter needs to have a monitoring and a resettable capacity.
In this project the target pollutant that will induce gene expression of the biological sensor is the mercury, this is based on the loss of green pigmentation in Arabidopsis thaliana. A substantially faster loss of chlorophyll is needed if is used as a reporter system for a plant sentinel. Chlorophyll loss in plants is normally a slow process that occurs during the complex mechanism of senescence. The half-life of chlorophyll has been estimated to be 2–5 days for relatively mature and fully greened leaves (Stobart and Hendry, 1984), visual perception of chlorophyll loss in leaves can take longer.
The process for whitening the plant requires following the method explained below takes around 48 hours in order to see a complete change in color. In order to accomplish this it is necessary to use specific enzymes which degrades the chlorophyll that is already in the plant and also a doubled stranded RNA which inhibits the production of an important molecule involved in the production of chlorophyll (Medford, J. et al , 2006).
Biosynthesis and Breakdown
The first phase of the chlorophyll biosynthesis starts with the glutamic acid, after nine chemical steps this amino acid produces a four ring structure, called protoporphyrin IX. A molecule of magnesium is add to the ring structure by the magnesium chelatase, through two more steps this is converted in monovinyl protochlorophyllide and is reduce to chlorophyllide a. by the enzyme protochlorophyllide oxidoreductase (POR). The chlorophyllide a. is transformed in darker green chlorophyll by the chlorophyll synthetase enzyme, this add a 20 carbon phytol tail.
The chlorophyll pathway degradation is an important catabolic process for the senescence of the leaf. This breakdown pathway starts with the chlorophyllase enzyme, which removes the hydrophobic twenty carbon phytol tail from the chlorophyll. As the synthetic pathway, the chlorophyll turn into the light green molecule called chlorophyllide. This molecule is converted to pheophorbide a. by the magnesium dechelatase enzyme at removing the magnesium and the red chlorophyll catabolite (RCC) is formed aside pheophorbide a oxygenase. Then the RCC reductase produces fluorescent chlorophyll catabolite (FCC). The FCC goes through different steps and its converted into nonfluorescent chlorophyll catabolites.
