(a) A stomach cell line growing in nutrient broth has a mutation in the gene encoding a particular type of tRNA. Assuming the mutation is not lethal to the cells, explain why the amount of SIRT3 mRNA in this cell line is identical to the amount produced by a normal stomach (NS) cell line but the amount of SIRT3 protein is less than in the NS cells. (b) Identify a dependent variable in the researchers' experiment shown in Figure 3. Justify the analysis of normal stomach cells (NS) in the experiments shown in Figure 3. Based on the data in Figures 1 and 3, describe the relationship between SIRT3 expression and glucose uptake. Calculate the percent change in lactic acid production by SC-1 cells compared with SC+RNA cells.
(c) Researchers analyzing regulation of SIRT3 gene expression engineer a SIRT3 gene that is identical to the normal gene except that the normal SIRT3 gene promoter is replaced by the promoter for a gene encoding a protein typically found only in human nerve cells. The researchers introduce this gene into normal human stomach cells to determine how much SIRT3 mRNA AND protein will be expressed from the engineered SIRT3 gene in the stomach cells. Predict the results of this experiment. The researchers claim that metabolic activity increases in cancerous cells. Provide reasoning based on the data provided to justify the claim. Based on the information provided, predict the cause of a decrease in CO2 production by the three groups of cancer cells (SC-1, SC+plasmid, and SC+RNA) treated with the compound that blocks the electron transport chain compared with the same groups of cells not treated with the compound.

(d) Based on the data provided, explain how testing for SIRT3 gene expression in samples of stomach cells might be used by physicians to predict which individuals have an increased risk of developing stomach cancer. Human stomach cells have plasma membrane receptors for the binding of certain extracellular signaling molecules such as growth factors. Explain why the irreversible binding of chemicals that mimic the growth factors will most likely change the normal cells into cancer cells.