Practise AP Biology 2.3 questions by connecting phospholipid bilayer structure and protein polarity to membrane organisation and internal cell conditions.
Many insects rely on pheromones (chemical signals) that are released by the females to find
mating partners. Scientists hypothesize that, in a certain type of moth, the behavior of male
moths in response to pheromones is regulated by the extracellular signaling molecule 20E.
Many receptors are embedded in the plasma membrane. Describe the polarity of the portion
of the receptor that is inside the membrane.
To investigate whether the binding of 20E to its receptor, DopEcR, affects behavior in moths,
scientists injected male moths with saline (control solution) or with small interfering RNA
molecules (siRNAs) that inhibit the expression of the gene encoding DopEcR. The scientists then
exposed the moths to the pheromone and determined the percent of total time observed that
the moths engaged in general activity, defined as movement in any direction. The scientists also
determined the percent of the general activity time that the moths spent in oriented activity,
defined as movement toward an area of high pheromone concentration (Table 1).
Table 1. Average General and Oriented Activity in Male Moths Injected With Saline or siRNA Molecules
DopEcR is a G protein-coupled receptor. When 20E binds to DopEcR, GTP displaces the GDP
bound to the G protein, and a signaling pathway is activated. The scientists hypothesize that this
leads to the transcription of genes associated with the oriented activity observed in the male
moths (Figure 1).
Figure 1. A simplified model of a signaling pathway activated by the binding of 20E to its receptor, DopEcR