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← Theoretical 2

Q57 — PIP2/PIP3 Signaling in T Cells — PTEN and Antigen Dose

Theoretical 2 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Immune Physiology Cell Signaling & Communication

After the antigen binds to the receptors on T cells, phosphatidylinositol-4-phosphate (PIP1) is phosphorylated to yield PIP2, which is then phosphorylated again resulting in PIP3. Both new lipid compounds are crucial messengers of the immune response. Results of a cell culture experiment to analyze this process are shown on the plots. Each trace is a time series for PIP2 or PIP3. There are four experimental groups in total: (1) stimulated with low dosage of the antigen; (2) stimulated with low dosage of antigen, while adding SF1670 (the inhibitor of enzyme PTEN, which is a key enzyme involved in lipid signaling); (3) stimulated with high dosage of antigen; (4) stimulated with high dosage of antigen, while adding SF1670.

Figure. Left plot: experimentally measured PIP2 concentration vs time. Right plot: PIP3 concentration vs time. Blue = low dosage stimulation, red = high dosage. Solid lines = no SF1670; dotted lines = SF1670 (PTEN inhibited) used. Figure. PIP2 (left) and PIP3 (right) concentration over time under four experimental conditions.

Determine whether the following statement are true or false:

A. PIP2 concentration quickly returns to initial levels even when the antigen is still present; thus, it cannot mediate long-term changes in cell fate
B. Presence of PTEN activity reliably increases the concentration ratio of PIP2 to PIP3
C. Concentration ratio of PIP2 to PIP3 contains information on the strength of the antigen.
D. Since antigen binding mediates production of PIP2, more antigen binding will result in more PIP2 under intact PTEN
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Question reproduced from IBO 2022, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)