Molecular transport and packing underlie increasing ribosome productivity in faster growing cells

Faster growing cells must make proteins more quickly. This occurs in part through increasing total ribosome abundance. However, the productivity of individual ribosomes also increases, almost doubling via an unknown mechanism. To investigate, we model both physical transport and chemical reactions among ensembles of individual molecules involved in translation elongation in Escherichia coli. We predict that the Damkohler number, the ratio of transport latency to reaction latency, for translation elongation is ~4; physical transport of individual ternary complexes accounts for ~80% of elongation latency. We also model how molecules pack closer together as growth quickens. Although denser cytoplasm both decreases transport distances and hinders motion, we predict that decreasing distance wins out, offering a simple mechanism for how individual elongating ribosomes become more productive as growth quickens. We also quantify how crowding imposes a physical limit on the performance of self-mixing molecular systems and likely undergirds cellular behavior more broadly.

Pharmacological Activity of (R)-(+)-Pulegone, a Chemical Constituent of Essential Oils

(R)-(+)-Pulegone is a monoterpene found in essential oils from plants of the Labiatae family. This compound is a major constituent of Agastache formosanum oil. In this study, the effect of (R)-(+)-pulegone on the central nervous system was evaluated. (R)-(+)-Pulegone caused a significant decrease in ambulation and an increase in pentobarbital-induced sleeping time in mice, indicating a central depressant effect. (+)-Pulegone also significantly increased the latency of convulsions as assessed by the pentylenetetrazole (PTZ) method. The antinociceptive properties of this monoterpene were studied in chemical and thermal models of nociception. Chemical nociception induced in the first and second phase of the subplantar formalin test was significantly inhibited by (R)-(+)-pulegone and was not blocked by naloxone. Thermal nociception was also significantly inhibited while (R)-(+)-pulegone increased the reaction latency of the mice in the hot plate test. These results suggest that (R)-(+)-pulegone is a psychoactive compound and has the profile of an analgesic drug.

Effects of Exercise on Choice Reaction Latency and Movement Speed

Performance and learning of an 8-choice RT-MT task was investigated as a function of two levels of interpolated arm exercise. Following a pretest under control nonexercise conditions, 90 subjects were given 60 trials under one of three experimental conditions (low intensity, high intensity, and vowel-cancelling). This was followed on a second day by a further 18 trials under control conditions. Predictions from the theory of exercise-induced activation received only limited support by the indication that the highly intense condition impaired RT. Exercise of low intensity did not facilitate RT. For MT no differential effects were found. Similarly, learning RT and MT was unaffected by exercise. These findings indicate that the theory of exercise-induced activation needs to be developed further to account for response situations that have high demand for attention.