A Level Biology Practice Exam

Where is mitochondrial DNA found?

1. In the nucleus

2. In the cytoplasm

3. Within the matrix of mitochondria

4. In the cell membrane

The correct answer is: Within the matrix of mitochondria

Mitochondrial DNA is indeed found within the matrix of mitochondria. Mitochondria are the powerhouses of the cell, and they contain their own DNA, which is distinct from the nuclear DNA found in the cell's nucleus. This DNA is circular and resembles bacterial DNA, supporting the endosymbiotic theory, which suggests that mitochondria were once independent prokaryotes that became incorporated into eukaryotic cells. The matrix of mitochondria is the innermost compartment, where various metabolic processes occur, including the citric acid cycle and oxidative phosphorylation. This environment is optimized for the functions of mitochondrial DNA, such as encoding proteins essential for ATP production and other mitochondrial functions. Other locations mentioned, like the nucleus or cytoplasm, do not contain mitochondrial DNA. The cell membrane is also unrelated to the storage of genetic material.