Q8 - Dominant-Negative Effects in Receptor Tyrosine Kinase Mutants

Theoretical 2 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Two different mutant forms of a gene that encodes a cell surface receptor tyrosine kinase (RTK) are separately inserted into vectors. One mutant encodes a protein with a non-functional kinase domain, and the other lacks a functional ligand binding domain. Each vector is separately introduced into normal cells that can express wild type RTK from their endogenous genes. It is known that the cells used have a high capacity for RTK receptors on their surface, that ligands bind to monomeric forms of receptor proteins and that heterodimeric receptors are inactive in signalling. The diagrams below depict four cell types identified. Each diagram shows the only receptor forms observed on the respective cell types in the ratio that they were observed. The experiments were performed under non-saturating concentrations of ligand.

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. In type 1 cells, the mutant receptor with the non-functional kinase domain will interfere with signalling by the cells' normal RTK.

B. In type 2 cells, the mutant RTK lacking functional ligand binding domain will be inactive for signalling, but will not interfere with normal signalling mediated by the cells' own receptor tyrosine kinases.

C. Equal levels of signalling will be achieved by type 3 and type 4 cells.

D. The effects of mutant RTKs of cell type 2 and cell type 3 on levels of signalling by the cells' own normal RTKs will be the same.

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Question reproduced from IBO 2018, 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)