Advanced Placement (AP) Biology Practice Exam

What role does the mitochondria play in terms of extranuclear genes?

1. It replicates nuclear DNA

2. It contains maternal extranuclear genes

3. It synthesizes proteins

4. It regulates gene expression

The correct answer is: It contains maternal extranuclear genes

Mitochondria are unique organelles within eukaryotic cells that possess their own set of DNA, known as mitochondrial DNA (mtDNA). This DNA is inherited maternally, meaning that it is passed down from mother to offspring. The presence of maternal extranuclear genes within mitochondria is significant because it contributes to certain traits and functions that are distinct from those governed by nuclear DNA. Mitochondrial DNA encodes for essential proteins involved in the processes of cellular respiration and energy production, but its most crucial role in the context of extranuclear genes lies in its inheritance pattern. Since this DNA is inherited exclusively from the mother, it can provide insights into maternal lineages and even evolutionary relationships among species. While the mitochondria do play a role in protein synthesis—specifically, they synthesize some of their own proteins using both their DNA and the cell's ribosomes—the primary focus in this context pertains to the genetic information they carry rather than the proteins themselves. Thus, the emphasis on maternal extranuclear genes accurately captures the unique genetic contribution of mitochondria in the cell.