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AP Biology 4.3 Signal Transduction Pathways Questions

Practise AP Biology 4.3 questions by linking signal transduction with differentiation, apoptosis, pathway mutations and altered cellular responses.

Syllabus
Effective Fall 2025
Course
AP Biology

Exam points

  • identify differentiation and apoptosis as possible cellular outcomes of signaling
  • predict how receptor or pathway mutations alter downstream signaling and phenotype
  • distinguish pathway activation or inhibition by chemicals, ligands and inhibitors
  • use pathway models and quantitative response data to predict changes in downstream molecules or cell behavior

Covered syllabus points

4.3.A—Describe the different types of cellular responses elicited by a signal transduction pathway4.3.B—Explain how a change in the structure of any signaling molecule affects the activity of the signaling pathway

Question 1

[Maximum number: 1]
B-cell activation model

B-cell activation model

As represented in the model above, B cells are activated by direct contact with antigens or stimulated helper T cells (TH)\left(\mathrm{T}_{\mathrm{H}}\right).

Based on the model, which of the following best describes an outcome of B cell activation?

A

Activated B cells differentiate into plasma cells and memory cells.

B

Activated B cells stimulate TH\mathrm{T}_{\mathrm{H}} cells to secrete antibodies.

C

Both B cells and TH\mathrm{T}_{\mathrm{H}} cells release chemical signals that negatively regulate antigen-presenting cells.

D

Plasma cells produce antibodies that activate additional B cells by a positive feedback mechanism.

Question 2

[Maximum number: 2]

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.

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

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

Figure 1. A simplified model of a signaling pathway activated by the binding of 20E to its receptor, DopEcR

Question (a)

(a)

C.

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Question (i)

(i)

The scientists studied some moths with a mutation in the gene encoding the G protein. The mutation prevents GTP from displacing the GDP bound to the G protein. Based on Figure 1, predict the effect of this mutation on the oriented activity in male moths exposed to the pheromone.

Expression of the gene encoding DopEcR is low in the male moths during their first few days as adults, when they are sexually immature. Gene expression rapidly increases as the moths reach sexual maturity. The scientists claim that this increase in gene expression increases the likelihood of males finding females with whom to mate.

[ 1 ]

Question (b)

(b)

D.

[ 1 ]

Question (i)

(i)

Based on Figure 1, explain how an inhibitor of the DopEcR pathway might serve as an effective chemical to protect crops from moth damage.

[ 1 ]
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