From resource to document: Scaffolding content and organising student learning in teachers’ documentation work on the teaching of series

We examine teachers’ use of resources as they prepare to teach the topic of numerical series of real numbers in order to identify how their personal relationship with mathematical content—and its teaching—interacts with their use of a commonly used textbook. We describe this interplay between textbook and personal relationship, a term coined in the Anthropological Theory of the Didactic (ATD, Chevallard, 2003), in the terms of documentation work (resources, aims, rules of action, operational invariants), a key construct from the documentational approach (DA, Gueudet & Trouche, 2009). We do so in the case of five post-secondary teachers who use the same textbook as a main resource to teach the topic. Documentational analysis of interviews with the teachers led to the identification of their aims and rules of action (the what and how of their resource use as they organise their teaching of the topic) as well as the operational invariants (the why for this organisation of their teaching). We describe the teachers’ documentation work in two sets of aims/rules of action: scaffolding mathematical content (series as a stepping stone to learning about Taylor polynomials and Maclaurin series) and organising student learning about series through drill exercises, visualisation, examples, and applications. Our bridging (networking) of theoretical constructs originating in one theoretical framework (personal relationship, ATD) with the constructs of a different, yet compatible, framework (documentation work, DA) aims to enrich the latter (teachers’ documentation work) with the individual agency (teachers’ personal relationship with the topic) provided by the former

Thioredoxin suppresses microscopic hopping of T7 DNA polymerase on duplex DNA

The DNA polymerases involved in DNA replication achieve high processivity of nucleotide incorporation by forming a complex with processivity factors. A model system for replicative DNA polymerases, the bacteriophage T7 DNA polymerase (gp5), encoded by gene 5, forms a tight, 1∶1 complex with Escherichia coli thioredoxin. By a mechanism that is not fully understood, thioredoxin acts as a processivity factor and converts gp5 from a distributive polymerase into a highly processive one. We use a single-molecule imaging approach to visualize the interaction of fluorescently labeled T7 DNA polymerase with double-stranded DNA. We have observed T7 gp5, both with and without thioredoxin, binding nonspecifically to double-stranded DNA and diffusing along the duplex. The gp5/thioredoxin complex remains tightly bound to the DNA while diffusing, whereas gp5 without thioredoxin undergoes frequent dissociation from and rebinding to the DNA. These observations suggest that thioredoxin increases the processivity of T7 DNA polymerase by suppressing microscopic hopping on and off the DNA and keeping the complex tightly bound to the duplex

The Grass Isn’t Always Greener: Perceptions of and Performance on Open-Note Exams

Undergraduate biology education is often viewed as being focused on memorization rather than development of students’ critical-thinking abilities. We speculated that open-note testing would be an easily implemented change that would emphasize higher-order thinking. As open-note testing is not commonly used in the biological sciences and the literature on its effects in biology education is sparse, we performed a comprehensive analysis of this intervention on a primary literature–based exam across three large-enrollment laboratory courses. Although students believed open-note testing would impact exam scores, we found no effect on performance, either overall or on questions of nearly all Bloom’s levels. Open-note testing also produced no advantage when examined under a variety of parameters, including research experience, grade point average, course grade, prior exposure to primary literature–focused laboratory courses, or gender. Interestingly, we did observe small differences in open- and closed-note exam performance and perception for students who experienced open-note exams for an entire quarter. This implies that student preparation or in-test behavior can be altered by exposure to open-note testing conditions in a single course and that ­increased experience may be necessary to truly understand the impact of this intervention