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← Theoretical A

Q25 — Mitochondrial RNase P Mutations and COXPD54

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Pedigree Analysis & Human Genetic Disorders Mitochondria & Chloroplasts: Structure & Endosymbiotic Origin

Mitochondrial RNase P is an endonuclease composed of three subunits (Figure 1B). Mutations in this enzyme are often associated with the development of combined oxidative phosphorylation deficiency syndrome (COXPD54) in humans. The figures below show various information regarding RNase P and its mutations.

Pedigrees A1 and A2 for two families with COXPD54, a diagram of the three RNase P subunits (TRMT10C, SDR5C1, PRORP) with mitochondrial targeting sequences marked, and a multi-species alignment of the RNase peptide segment with mutation positions X, Y, and Z highlighted in orange. Figure 1. A1 & A2 are pedigrees of two families showing distinct missense mutations resulting in the COXPD54 syndrome in shaded individuals; mutation X for A1 and mutation Y for A2. B RNase P subunits; (MTS - mitochondrial targeting sequence). C Alignment results of the RNase peptide segment across various organisms. Positions affected by the mutations are highlighted in orange boxes. The mutations leading to COXPD54 syndrome are Tyr (Y) → His (H) in position X; Thr (T) → Ala (A) in position Y; Ala (A) → Val (V) in position Z.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Within the primary structure, it can be assumed that the mutation at position X is located closer to the active site of the enzyme than the mutation at position Z.
B. Mutation at position Y involves transversion (purine to pyrimidine change).
C. All of the RNase P subunits assemble within the cytoplasm before being transported into the mitochondrion.
D. Knowing that individual II-3 (A1) is the carrier of mutation at position X, the probability of the couple II-3 (A1) and II-2 (A2) having a child with the syndrome is 1/6. (Assume Mendelian inheritance.)
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Question reproduced from IBO 2024, Theoretical Exam Part A, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)