All are true about human mitochondrial DNA except
**Core Concept**
Mitochondrial DNA (mtDNA) is a double-stranded circular DNA molecule found in the mitochondria, often referred to as the "powerhouse" of the cell. mtDNA is inherited maternally, as only egg cells contribute mitochondria to the fertilized egg. It encodes for 13 proteins essential for the electron transport chain, which generates ATP during oxidative phosphorylation.
**Why the Correct Answer is Right**
The correct answer will be an option that contradicts the established facts about human mtDNA. Each of the options given will be analyzed below.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because mtDNA is indeed encoded for 13 of the 22 proteins involved in the electron transport chain. However, the majority of the proteins involved in the electron transport chain are encoded by the nuclear DNA and synthesized in the cytosol.
**Option B:** This option is incorrect because mtDNA does indeed exhibit genetic drift, which is the random change in the frequency of a gene variant in a population over time. This phenomenon is a characteristic feature of mtDNA due to its maternal inheritance pattern.
**Option C:** This option is incorrect because mtDNA does indeed exhibit a high rate of mutation due to its lack of histone protection and exposure to reactive oxygen species. This high mutation rate can lead to various diseases, including neurodegenerative disorders.
**Option D:** This option is incorrect because mtDNA does indeed have a distinct genetic code compared to nuclear DNA. The genetic code used by mtDNA is similar to, but not identical to, the standard genetic code used by nuclear DNA.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that mtDNA mutations can lead to a range of disorders, known as mitochondrial myopathies, which affect the muscles and nervous system. These disorders are often characterized by exercise intolerance, muscle weakness, and other systemic symptoms.
**Correct Answer:** A. mtDNA is encoded for 13 proteins essential for the electron transport chain, but the majority of the proteins involved in the electron transport chain are encoded by the nuclear DNA and synthesized in the cytosol.