AP Biology 2.3.A Cell Membrane Components

Practise AP Biology 2.3.A questions by orienting phospholipid heads and tails and identifying hydrophobic protein regions that interact inside the membrane.

[Maximum number: 1]

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

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2.3.A—Describe the roles of each of the components of the cell membrane in maintaining the internal environment of the… question 1