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Answers-to-Lecture-Q_40924 - Answers to Lecture Questions...

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Unformatted text preview: Answers to Lecture Questions from 2‐22‐10 & 2‐24‐10 Lectures (Question numbers below match those in the VNET document, “1362 CH 17‐20 Questions to be covered during lecture”) 1. Carry out the following transcription and translation problem: 4. E. coli is cultured on a growth medium containing both tryptophan and lactose. In these cells: A. Is transcription of the trp operon occurring? No, not necessary to transcribe trp operon since tryptophan is supplied to the cells in the growth medium. B. Is the lactose repressor active or inactive? Inactive; in order for cells to use the supplied lactose, lac operon must be transcribed to synthesize the enzymes for lactose utilization. C. What happens once the cells use up the tryptophan? Cells will need to make their own tryptophan once it is used up, thus the repressor will become inactivated, and transcription of trp operon will occur. 2 5. A bacterial species has been found to synthesize three enzymes for the production of substance X: A → B → C → X When these cells are cultured in growth medium containing substance X, the 3 enzymes are not detected. How would one characterize the substance X operon? A. Inducible B. Repressible C. Neither A or B Answer: Repressible; the presence of “X” represses (prevents) transcription of “X” operon structural genes (which is why the enzymes of the pathway are not detected). Similar to question #9: Which level of gene expression is not correctly matched? A. B. C. D. E. Answer: “A”; transcriptional control determines whether or not a transcript will be made; post‐ transcriptional control involves mechanisms using the synthesized transcript, such as mRNA degradation due to removal of 5’ cap or 3’ polyA tail or splicing. Transcriptional: mRNA is degraded Post‐transcriptional: splicing exons together Translational: affect ribosome function Post‐translational: protein is modified Transcriptional: lac repressor binds operator ...
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