BIOL 121 (2011) Fall Exam 3 + Key

9 biol 121

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Unformatted text preview: you lost 1 point. b) You isolate a mutant E. coli that, when growing on lactose, produces more beta- galactosidase than does the wild- type strain. You also find that the rate of transcription of the lac operon (number of mRNA molecules produced per second) is the same for the mutant and wild- type strains. List three possible explanations for these observations. (6 pts) Answer: The beta- galactosidase protein could have a shorter half- life in the wildtype strain. The lac mRNA could have a shorter half- life in the wildtype strain. The lacZ gene may be translated less efficiently in the wildtype strain GRADER NOTE: Each of the three possibilities was worth 2 points, totaling to 6 points. There could be a few possibilities, but some reasonable answers could have been related to degradation levels, and post-transcriptional and/or post-translational modifications. For example, one could have mentioned microRNA regulation. No credit was given if there was any mention of an effect that may have effected transcription rate in any way or if the explanation was highly improbable. c) You engineer a new strain of E. coli so that the lacI gene, which encodes lac repressor, is now in an operon with lacZ, lacY, and lacA (i.e. all four genes are transcribed on a single mRNA). Will 8 BIOL 121 NAME: Exam 3 12/5/2011 these engineered E. coli cells increase the synthesis of beta- galactosidase when they are shifted from growth on glucose to growth on lactose? (Briefly explain your reasoning.) (6 pts) Answer: The synthesis of beta- galactosidase will increase when cells ar...
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