Percentage of mitochondrial DNA out of total cellular DNA is?

**Core Concept**
Mitochondrial DNA (mtDNA) is a separate entity from nuclear DNA (nDNA) and plays a crucial role in the synthesis of proteins essential for energy production in cells. The proportion of mtDNA to total cellular DNA is a critical aspect of mitochondrial biology.

**Why the Correct Answer is Right**
Mitochondrial DNA constitutes a small fraction of the total cellular DNA, approximately 1-2% in humans. This is because mtDNA is a circular, double-stranded molecule of approximately 16,500 base pairs, whereas the human genome has a total of approximately 3.2 billion base pairs of DNA. The low percentage of mtDNA is due to the limited number of mitochondria in a typical cell, despite the high energy demands of cells, especially in tissues with high metabolic rates such as the brain and muscle.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the actual percentage of mtDNA is not around 10-20%. While it is true that mtDNA is a small fraction of the total cellular DNA, the specific percentage is lower than this range.
**Option B:** This option is incorrect because the actual percentage of mtDNA is not around 5%. While it is true that mtDNA is a small fraction of the total cellular DNA, the specific percentage is lower than this value.
**Option C:** This option is incorrect because the actual percentage of mtDNA is not around 50%. This value is grossly overestimated and does not accurately reflect the proportion of mtDNA to total cellular DNA.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that mitochondrial DNA mutations can lead to a range of diseases, including neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease. Understanding the proportion of mtDNA to total cellular DNA is crucial for appreciating the significance of mitochondrial dysfunction in various clinical contexts.

**Correct Answer:** C. 1-2%.