Tryptophan synthase is one of the enzymes synthesized from the trp mRNA. In wildâtype E. coli, the trp mRNA has a short halfâlife, but the tryptophan synthase halfâlife is much longer. To investigate how changes to the stability of the enzyme or its mRNA affect enzyme activity, two strains of E. coli were engineered. Strain A stabilizes the trp mRNA and strain B rapidly degrades tryptophan synthase. The wildâtype, A, and B strains were grown in a medium with glucose as the sole carbon source. After several generations, tryptophan was added to all three cultures and tryptophan synthase activity was measured periodically.

Select the statements that describe the expected change in tryptophan synthase activity after the addition of tryptophan
Note: Evaluate each condition as a simple model, where changes in the stability of trp mRNA or tryptophan synthase do not elicit secondary effects in the cells

A. In the wild-type strain, trp mRNA is unstable and will be degraded rapidly. As the cells continue to divide, trýptophan synthase will be diluted out and enzyme activity per cell will decrease
B. In strain A, the trp mRNA is stable and tryptophan synthase will continue to be synthesized However, as the cultures grow the tryptophan synthase will be diluted and the amount of enzyme activity will slowly decrease
C. In the wild-type strain, the trp mRNA is degraded rapidly. However, since the tryptophan synthase is stable, the enzyme activity per cell will remain unchanged as the cells divide
D. In strain A, the trp mRNA is stable but the presence of tryptophan in the medium will cause the degradation of tryptophan synthase and abruptly decrease enzyme activity
E. In strain B, since both the trp mRNA and tryptophan synthase are rapidly degraded, the enzymee activity will drastically decrease.