Mitochondrial-encoded genes vs Nuclear-encoded mitochondrial proteins
How to tell Mitochondrial-encoded genes and Nuclear-encoded mitochondrial proteins apart when a board question makes them look alike.
Mitochondrial-encoded disease follows maternal heteroplasmy; nuclear-encoded mitochondrial disease follows Mendelian inheritance and import targeting.
Side by side
Mitochondrial-encoded genes are maternally inherited mtDNA genes encoding 13 oxidative phosphorylation proteins, 22 tRNAs, and 2 rRNAs, with heteroplasmy and high mutation rate.
Most mitochondrial proteins are nuclear encoded, inherited by Mendelian patterns, translated in cytosol, and imported into mitochondria.
Mitochondrial DNA is circular, lacks protective histones, has limited repair, and is passed through oocyte cytoplasm.
Nuclear genes encode most respiratory chain subunits, assembly factors, replication proteins, and metabolic enzymes targeted to mitochondria.
Maternal-only transmission, heteroplasmy, and mtDNA mutation support mitochondrial-encoded disease.
Autosomal or X-linked pedigree with mitochondrial dysfunction supports nuclear-encoded mitochondrial protein disease.
The trap
A mitochondrial phenotype does not prove mitochondrial DNA inheritance because many mitochondrial proteins come from nuclear genes.
The repair move
For mitochondrial disease, separate organelle location from inheritance of the mutated gene.
Try a free question
CoreA 22-year-old man develops sudden bilateral painless central vision loss over weeks, with optic disc edema and telangiectasias on funduscopy. His mother and two maternal uncles had similar vision loss. Genetic testing reveals a point mutation in MT-ND4 (mtDNA-encoded subunit of complex I of the electron transport chain). Which inheritance pattern fits?
Show answer and explanation
Answer: A. Mitochondrial inheritance. Leber hereditary optic neuropathy (LHON) is caused by mtDNA mutations in respiratory complex I subunits (most commonly MT-ND4, MT-ND1, MT-ND6). Maternal-only transmission, variable penetrance (males more often affected), and heteroplasmy explain the family pattern.
Why the other choices are tempting
- B. Autosomal dominant inheritance allows father-to-son transmission, which is not seen here.
- C. Autosomal recessive requires carrier parents; the maternal-line pattern fits mitochondrial inheritance.
- D. X-linked recessive has carrier mothers and affected sons but lacks maternal-only transmission with daughters at risk.
- E. X-linked dominant has affected fathers transmitting to all daughters, not the pattern here.
Flashcards
Tap a card to flip it.
What clue supports Mitochondrial-encoded genes?
Choose Mitochondrial-encoded genes when the stem gives this pattern: Mitochondrial-encoded genes are inherited maternally, reside in mitochondrial DNA, and encode a small subset of oxidative phosphorylation proteins plus mitochondrial rRNAs and tRNAs.
What clue supports Nuclear-encoded mitochondrial proteins?
Choose Nuclear-encoded mitochondrial proteins when the stem gives this contrasting pattern: Most mitochondrial proteins are nuclear encoded, inherited by Mendelian patterns, translated in cytosol, and imported into mitochondria.
Quick answers
What is the fastest way to tell Mitochondrial-encoded genes from Nuclear-encoded mitochondrial proteins?
Mitochondrial-encoded disease follows maternal heteroplasmy; nuclear-encoded mitochondrial disease follows Mendelian inheritance and import targeting.
What is the key clue for Mitochondrial-encoded genes?
Mitochondrial-encoded genes are maternally inherited mtDNA genes encoding 13 oxidative phosphorylation proteins, 22 tRNAs, and 2 rRNAs, with heteroplasmy and high mutation rate.
What is the key clue for Nuclear-encoded mitochondrial proteins?
Most mitochondrial proteins are nuclear encoded, inherited by Mendelian patterns, translated in cytosol, and imported into mitochondria.
What is the common trap with Mitochondrial-encoded genes vs Nuclear-encoded mitochondrial proteins?
A mitochondrial phenotype does not prove mitochondrial DNA inheritance because many mitochondrial proteins come from nuclear genes.