SAT Subject Biology Practice Question 462: Answer and Explanation
12. Questions below refers to the following experiment involving human liver cells.
Aspartate aminotransferase (AAT) is an enzyme produced in liver cells that catalyzes an important step in the metabolism of amino acids. The production of AAT is dependent upon various hormonal stimuli. Human liver cells were cultured; half the cultured cells were used to measure the amount of AAT mRNA present, and half were used to measure the amount of AAT present. Measurements were taken at five-minute intervals following hormonal stimulation of the cells.
Figure 1 shows the results of this experiment.
The experiment was repeated, this time adding an inhibitor of protein synthesis along with the hormone.
Figure 2 shows the results of this experiment.
A. mRNA production does not require an enzyme
B. mRNA is not a protein
C. the enzyme needed to make mRNA is not a protein
D. the enzyme needed to make mRNA still needs to be translated
E. the enzyme needed to make mRNA is already present in the cell
Correct Answer: E
E An inhibitor of protein synthesis will affect the production of new proteins only, not previously existing proteins. Because the enzyme needed to make the mRNA is already present, it is available to transcribe the AAT mRNA. Choices A and C are contradicted by the question, which states that mRNA production is run by an enzyme and that the enzyme is a protein. Choice B is true; however, the enzyme needed to make mRNA is a protein, and this is what the question is asking about. Don't fall into the temptation trap-be sure you know what the question is asking before you choose an answer! Choice D is false-if this enzyme still needed to be translated, no mRNA production could occur and the figure shows that mRNA production is occurring.