Andreas Mershin

Molecular vibration-sensing component in Drosophila melanogaster olfaction

A common explanation of molecular recognition by the olfactory system posits that receptors recognize the structure or shape of the odorant molecule. We performed a rigorous test of shape recognition by replacing hydrogen with deuterium in odorants and asking whether Drosophila melanogaster can distinguish these identically shaped isotopes. We report that flies not only differentiate between isotopic odorants, but can be conditioned to selectively avoid the common or the deuterated isotope. Furthermore, flies trained to discriminate against the normal or deuterated isotopes of a compound, selectively avoid the corresponding isotope of a different odorant. Finally, flies trained to avoid a deuterated compound exhibit selective aversion to an unrelated molecule with a vibrational mode in the energy range of the carbon–deuterium stretch. These findings are inconsistent with a shape-only model for smell, and instead support the existence of a molecular vibration-sensing component to olfactory reception.

Effect of varying electric potential on surface-plasmon resonance sensing.

The high sensitivity of surface-plasmon resonance (SPR) sensors allows measurements of small variations in surface potentials to be made. We studied the changes of the SPR angle when an oscillating electric potential was applied to a gold film on which surface plasmons were excited. The shifts of the SPR resonance angle were observed for various aqueous solutions as an adjacent medium. A model that takes into account the redistribution of charges at the double layer near the metal-liquid interface as well as the oxidation of the gold film was developed. It was found that a change in the electronic density at voltages below the oxidation potential and, in addition, the oxidation of the gold surface above this potential are the main mechanisms that account for the observed dependences. It was shown that relatively slow oxidation-reduction processes can explain the observed hysteresis effect. Application of these techniques to studies of dielectric properties and conformational changes of polar biomolecules, such as tubulin, are discussed.

Towards Experimental Tests of Quantum Effects in Cytoskeletal Proteins

This volume is appropriately titled “The Emerging Physics of Consciousness” and much of it is focused on using some aspect of “quantum weirdness” to solve the problems associated with the phenomenon of consciousness. This is sometimes done in the hope that perhaps the two mysteries will somehow cancel each other through such phenomena as quantum coherence and entanglement or superposition of wave functions.

Surface plasmon resonance study of the actin-myosin sarcomeric complex and tubulin dimers

Abstract Biosensors based on the principle of surface plasmon resonance (SPR) detection were used to measure biomolecular interactions in sarcomeres and changes in the dielectric constant of tubulin samples with varying concentration. At SPR, photons of laser light efficiently excite surface plasmons propagating along a metal (gold) film. This resonance manifests itself as a sharp minimum in the reflection of the incident laser light and occurs at a characteristic angle. The dependence of the SPR angle on the dielectric permittivity of the sample medium adjacent to the gold film allows the monitoring of molecular interactions at the surface. We present results of measurements of cross-bridge attachment-detachment within intact mouse heart muscle sarcomeres and measurements on bovine tubulin molecules pertinent to cytoskeletal signal transduction models.

Integrating Web-Based Teaching Tools into Large University Physics Courses

Acquiring the mathematical, conceptual, and problem-solving skills required in university-level physics courses is hard work, and the average student often lacks the knowledge and study skills they need to succeed in the introductory courses. Here we propose a new pedagogical model and a straight-forwardly reproducible set of internet-based testing tools. Our work to address some of the most important student deficiencies is based on three fundamental principles: balancing skill level and challenge, providing clear goals and feedback at every stage, and allowing repetition without penalty. Our tools include an Automated Mathematics Evaluation System (AMES), a Computerized Homework Assignment Grading System (CHAGS), and a set of after-homework quizzes and mini-practice exams (QUizzes Intended to Consolidate Knowledge, or QUICK). We describe how these tools are incorporated into the course, and present some preliminary results on their effectiveness.

Reply to Hettinger: Olfaction is a physical and a chemical sense in Drosophila

We would like to thank Dr. Hettinger (1) for his positive comment on our results showing that flies can discriminate isotopes by smell and are capable of cross-learning between odorants sharing a molecular vibration. Our article (2) demonstrated the presence of a physical (vibrational) component to odor character necessitating a vibration-sensing mechanism, the nature of which was not addressed experimentally and remains to be elucidated. We suggest that it likely involves inelastic electron tunneling, because this is consistent with our experimental data and with Brookes et al. (3), who have shown that an inelastic tunneling mechanism in olfaction is physically plausible. As pointed out by Luca Turin, this odorant detection mechanism does not require generation of free electrons by NADPH (4) and offers a potential explanation to why most enantiomer pairs smell identical. Further, Takane and Mitchell (5) have found IR spectra to be good predictors of odor character.

New Pedagogy for Using Internet-Based Teaching Tools in Physics Course

Acquiring the mathematical, conceptual, and problem-solving skills required in university-level physics courses is hard work, and the average student often lacks the knowledge and study skills they need to succeed in the introductory courses. Here we propose a new pedagogical model and a straight-forwardly reproducible set of internet-based testing tools. Our work to address some of the most important student deficiencies is based on three fundamental principles: balancing skill level and challenge, providing clear goals and feedback at every stage, and allowing repetition without penalty. Our tools include an Automated Mathematics Evaluation System (AMES), a Computerized Homework Assignment Grading System (CHAGS), and a set of after-homework quizzes and mini-practice exams (QUizzes Intended to Consolidate Knowledge, or QUICK). We describe how these tools are incorporated into the course, and present some preliminary results on their effectiveness.