Unassigned Codons, Nonsense Suppression, and Anticodon Modifications in the Evolution of the Genetic Code

The origin of the genetic code is a central open problem regarding the early evolution of life. Here, we consider two undeveloped but important aspects of possible scenarios for the evolutionary pathway of the translation machinery: the role of unassigned codons in early stages of the code and the incorporation of tRNA anticodon modifications. As the first codons started to encode amino acids, the translation machinery likely was faced with a large number of unassigned codons. Current molecular scenarios for the evolution of the code usually assume the very rapid assignment of all codons before all 20 amino acids became encoded. We show that the phenomenon of nonsense suppression as observed in current organisms allows for a scenario in which many unassigned codons persisted throughout most of the evolutionary development of the code. In addition, we demonstrate that incorporation of anticodon modifications at a late stage is feasible. The wobble rules allow a set of 20 tRNAs fully lacking anticodon modifications to encode all 20 canonical amino acids. These observations have implications for the biochemical plausibility of early stages in the evolution of the genetic code predating tRNA anticodon modifications and allow for effective translation by a relatively small and simple early tRNA set

Interdisciplinary education – a predator–prey model for developing a skill set in mathematics, biology and technology

The science of biology has been transforming dramatically and so the need for a stronger mathematical background for biology students has increased. Biological students reaching the senior or post-graduate level often come to realize that their mathematical background is insufficient. Similarly students in a mathematics programme, interested in biological phenomena find it difficult to master the complex systems encountered in biology. In short, the biologists do not have enough mathematics and the mathematicians are not being taught enough biology. The need for interdisciplinary curricula that includes disciplines such as biology, physical science, information technology, and mathematics is widely recognized, but has not been widely implemented. In this paper it is suggested that mathematical biology students develop a skill set of biology (ecology), mathematics, modeling and technology to encourage working across disciplinary boundaries. To illustrate such a skill set a predator-prey model that contains self-limiting factors for both predator and prey, is suggested. The general idea of dynamics, as described by differential equations is introduced and students are encouraged to discover the applicability of this approach to the dynamics of more complex biological systems. The level of mathematics and technology required is not advanced; therefore it is ideal for inclusion in a senior-level or introductory graduate level course for students interested in mathematical biology in which three important disciplines - biology, mathematics and technology - come together to develop a skill set for prospective researchers.http://www.tandfonline.com/loi/tmes202018-02-06hb2017Mathematics and Applied Mathematic

Gehalten aan lood, cadmium, kwik en arseen in monsters vlees en organen van runderen en varkens

In het kader van het VREK-monitoringsprogramma zijn analyseresultaten betreffende lood, cadmium, kwik en arseen over 1978, 1979 en 1980 geinventariseerd en geevalueerd. Het betreft hier analyseresultaten voor monsters rundvlees, varkensvlees, pluimveevlees, eieren, rundernier, varkensnier en kippelever

Review of a predator-prey model with two limit cycles

It is well-known that the Lotka–Volterra predator-prey model has a family of periodic orbits, but does not possess limit cycles and therefore the model is said to be structurally unstable. The Lotka–Volterra model is a special case of a much larger group namely the quadratic population models and it can be shown that none of them can produce limit cycles. The surprising finding is that by combining two quadratic models a quadratic population model with two limit cycles is uncovered. Although the model looks simple at first glance it provides a rich source of dynamics and deserves attention. In this paper, we revisit a model that has its origin in the work of Dubois and Closset. A set of two quadratic population models interact as piecewise defined differential equations. The model has been discussed by Ren Yongtai and Han Li, cryptically written and showing some linguistic and typographical errors, but providing an excellent vehicle for developing skills in mathematical modelling, differential equations and technology for the young researcher. We explore the model in clearer detail and supplement the theory with rich graphical illustration. The paper has the purpose of providing an example of how a young researcher, such as a postgraduate student in biomathematics, can expand on an existing model by making use of current technology.http://www.tandfonline.com/loi/tmes202019-08-20hj2018Mathematics and Applied Mathematic

Cause–effect analysis : improvement of a first year engineering students’ calculus teaching model

This study focuses on the mathematics department at a South African university and in particular on teaching of calculus to first year engineering students. The paper reports on a cause-effect analysis, often used for business improvement. The cause-effect analysis indicates that there are many factors that impact on secondary school teaching of mathematics, factors that the tertiary sector has no control over. The analysis also indicates the undesirable issues that are at the root of impeding success in the calculus module. Most important is that students are not encouraged to become independent thinkers from an early age. This triggers problems in follow up courses where students are expected to have learned to deal with the work load and understanding of certain concepts. A new model was designed to lessen the impact of these undesirable issues.http://www.tandfonline.com/loi/tmes202017-06-30hb2016Mathematics and Applied Mathematic

Развитие экстремального туризма в Крыму

Целью данной работы является на основе географического анализа факторов становления и особенностей развития экстремального туризма в Крыму разработать рекомендации по усовершенствованию данной отрасли туристской деятельности для создания привлекательного образа Крыма на международной арене