BIOL 2117 Exam 3 Questions and Answers

What types of enzymes are typically constitutively expressed? Ans- enzymes in constant demand In an experiment exploring the expression of DNA repair enzymes, phage exposed to UV light had low infectivity, but when both phage and host cell E. coli were exposed to UV light, normal levels of infectivity resulted. From these data we can infer Ans- host cell genes were used to repair phage DNA The lacZ gene was used in an experiment testing for the expression of gene X. About half the resulting colonies were blue when grown on agar supplemented with X-Gal and about half were white. This means Ans- the blue colonies expressed gene X and the white colonies did not How are alternative sigma factors different from regulons? Ans- Alternative sigma factors are coordinated regulons; many different regulons initiated by separate, but related activators, but operating simultaneously. Attenuation is not a viable mechanism to regulate eukaryal gene expression of the trp operon because Ans- transcription and translation are physically separated in eukaryal cells Attenuation works as a gene regulation mechanism in prokaryal cells because Ans- single stranded mRNA is able to fold and form complementary double stranded regions Attenuation is not a viable mechanism to regulate eukaryal gene expression of the trp operon because Ans- positive control because the interaction between AHL (autoinducer) and LuxR regulator results in greater binding and expression of luxR. In experiments with the