Using Stock and Flow Modeling to Address Knowledge Gaps in Marine Plastic Pollution Data

As plastic becomes a ubiquitous part of society, its growth outpaces waste disposal infrastructure and enters the environment as physical and chemical pollution. Plastic can also erode during the use cycle and reach the environment without any chance of being arrested by collection efforts. Plastic is a hazard to many parts of the earth’s life support system but there are many knowledge gaps regarding the processes by which plastic moves through the use cycle and environment. In particular, the ocean is generally regarded as a sink for plastic out of which it is difficult to escape, but plastic can sink into the benthic zone reaching a deeper and more permanent sink and affecting a different environment. Little is known about the rate plastic moves from the surface to the benthic zone, the time it spends on the surface, and the quantity already in the benthic zone. To address these knowledge gaps, a stock and flow model was constructed using FORTRAN to simulate as much of the plastic use, disposal, and pollution cycle as was feasibly possible. The constructed model allowed for a complex use of Residence Time Distributions (RTDs), with plastic exiting a stock at variable rates and percentages based on the quantity of plastic entering the stock. This model was then cross-referenced with real data on surface ocean plastic, plastic waste, and other known quantities to check the accuracy of the simulation. Once it was determined that the model’s derived values for quantities that have been accurately measured in real life were within acceptable margins, the model’s values for the RTDs of plastic in the ocean were deemed reasonable. The model was also used to project plastic pollution into the future using several different scenarios to obtain estimates on future plastic production and pollution as well as the effects of RTDs on various stocks in the model. The model produced in this research could be scaled to different regions by changing the production value of the plastic entering the model and the plastic use quantities and waste disposal methods and rates

Altering the stability of the Cdc8 overlap region modulates the ability of this tropomyosin to bind cooperatively to actin and regulate myosin.

Tropomyosin (Tm) is an evolutionarily conserved ?-helical coiled-coil protein, dimers of which form end-to-end polymers capable of associating with and stabilising actin-filaments and regulate myosin function. The fission yeast, Schizosaccharomyces pombe, possesses a single essential Tm, Cdc8, which can be acetylated on its amino terminal methionine to increase its affinity for actin and enhance its ability to regulate myosin function. We have designed and generated a number of novel Cdc8 mutant proteins with amino terminal substitutions to explore how stability of the Cdc8-polymer overlap region affects the regulatory function of this Tm. By correlating the stability of each protein, its propensity to form stable polymers, its ability to associate with actin and to regulate myosin, we have shown the stability of the amino terminal of the Cdc8 ?-helix is crucial for Tm function. In addition we have identified a novel Cdc8 mutant with increased amino-terminal stability, dimers of which are capable of forming Tm-polymers significantly longer than the wild-type protein. This protein had a reduced affinity for actin with respect to wild type, and was unable to regulate actomyosin interactions. The data presented here are consistent with acetylation providing a mechanism for modulating the formation and stability of Cdc8 polymers within the fission yeast cell. The data also provide evidence for a mechanism in which Tm dimers form end-to-end polymers on the actin-filament, consistent with a cooperative model for Tm binding to actin