Mitochondrial DNA (mtDNA) is a circular DNA molecule found in yeast mitochondria. In a particular strain of Saccharomyces cerevisiae, it is 85,800 base pairs long and contains protein-coding genes as well as non-coding control regions.
Researchers investigated whether a single nucleotide mutation in a non-coding control region of mtDNA affected cellular tolerance to oxidative stress (induced by hydrogen peroxide, H2O2\text{H}_2\text{O}_2H2O2).
- Strain T had Thymine at nucleotide position 8,420.
- Strain C had a mutation resulting in Cytosine at nucleotide position 8,420.
The control regions of both Strain T and Strain C were the same length.
Name the type of gene mutation that is most likely to have occurred at nucleotide position 8,420.
Strain T and Strain C were exposed to a 48-hour oxidative stress treatment using hydrogen peroxide. The scientists measured:
- Oxygen consumption rate (JO2J_{\text{O}_2}JO2), which indicates the rate of aerobic respiration.
- Cox1 protein abundance (a mitochondrially encoded polypeptide essential for the respiratory electron transport chain).
They calculated the percentage decrease in these measurements for both groups at the end of the 48 hours compared to the start of the treatment.
Figure 1 and Figure 2 show their results.
A student concluded from Figure 1 and Figure 2 that oxidative stress has a more severe damaging impact on aerobic respiration and mitochondrial function in Strain C than in Strain T.
Evaluate the student's conclusion.
The mtDNA control region is non-coding but initiates both mtDNA replication and the transcription of mitochondrial messenger RNA (mRNA).
Use this information to suggest two reasons why the mutation at position 8,420 in Strain C could lead to the larger decrease in Cox1 protein level seen in Figure 2.