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Unformatted text preview: Name: TF Name: 1 LS1a Problem Set #10 and Lab #9 Post-Lab Question Both assignments due Monday 12/15 at noon in your TFs drop box on the 2 nd floor of the Science Center (100 problem set points + 30 lab points) Lab 9 post-lab question (30 points) : 1) Briefly summarize the results you obtained for each strain of bacteria tested in the lac operon lab. Based on your results, what is the identity of each strain? (10 points for recording results) Expected results: Strain 10 lacI- Strain 20 lacZ- Strain 30 lacY- Strain 40 wt Media A (glycerol) Yellow Clear Clear Clear Media B (lactose) Yellow Clear Clear Yellow Media C (glycerol/TMG) Yellow Clear Yellow Yellow Media D (glucose/lactose) Yellow Clear Clear Clear (20 points for explanation) Strain 10 produces -galactosidase at all times regardless of the presence or absence of lactose and glucose. This suggest that no activation is required nor any repression is observed indicative of the lac repressor (lacI) mutation. Strain 20 never produces any -galactosidase. The simplest explanation for this result is that the lacZ gene is defective. Strain 30 is unable to produce any -galactosidase except when TMG is present. These bacteria are unable to respond to lactose present in the media. Since TMG can induce lac operon expression independently from the lac permease, it is most probable that this strain has the lac permease (lacY) mutation. Strain 40 does not produce -galactosidase when grown on glycerol (no positive induction) or on glucose/lactose (repression from glucose). However it does produce - galactosidase when TMG is in the media or when only lactose is present. Therefore lactose is able to enter the cell, indicative that the lac permease is functioning, and given the possibilities this strain should be wildtype. Name: TF Name: 2 LS1a Problem Set #10 Due Monday 12/15 at noon in your TFs drop box on the 2 nd floor of the Science Center 1. (24 points) The transcription of the lacZ gene in E. coli bacteria is regulated in part by the binding of the lac repressor protein to the lac promoter. When bacteria are grown in media containing only glucose and no lactose, no -galactosidase enzyme is produced. When bacteria are grown in media containing only lactose, increased levels of -galactosidase enzyme are made....
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This document was uploaded on 03/23/2011.
- Spring '11