QUESTION 1: How will transcription of the lac operon be affected when you add la
ID: 224837 • Letter: Q
Question
QUESTION 1: How will transcription of the lac operon be affected when you add lactose to the media of lacIsmutant E. coli?
A. No change, and transcription of lac operon will continue at a high level
B. No change, and transcription of lac operon will continue to be repressed
C. increase in lac operon transcription, much higher than before lactose was added
D. Small increase in lac operon transcription, just a little higher than before lactose was added
QUESTION 2: Same question as above, but this time the mutant is lacO-(an inactivating mutation in the lac operator sequence).
A. No change, and transcription of the lac operon will continue at a high level
B. No change, and transcription of the lac operon will continue to be repressed
C. Large increase in lac operon transcription, much higher than before lactose was added
D. Small increase in lac operon transcription, just a little higher than before lactose was added
QUESTION 3: Which of the following is true for a eukaryotic gene?
A. An enhancer DNA element can influence a gene's expression in a tissue-specific manner, while the promoter DNA element is not tissue-type specific.
B. An enhancer DNA element is not bound by proteins, while a promoter DNA element is.
C. In the presence of the promoter, but no enhancer DNA elements, there will be absolutely no transcription of a gene.
D. There is usually only one enhancer DNA element per gene.
A. No change, and transcription of lac operon will continue at a high level
B. No change, and transcription of lac operon will continue to be repressed
C. increase in lac operon transcription, much higher than before lactose was added
D. Small increase in lac operon transcription, just a little higher than before lactose was added
Explanation / Answer
QUESTION 1: How will transcription of the lac operon be affected when you add lactose to the media of lacIs mutant E. coli?
ANSWER: B. No change, and transcription of lac operon will continue to be repressed
LacI is a Repressor i.e the gene encoding for the lac repressor protein- in the absence of lactose the repressor protein binds to the operator and blocks binding of RNA polymerase at promoter.
lacIs be can be identified as a Superrepressor i.e repressor cannot be inactivated by inducer (Lactose).
QUESTION 2: Same question as above, but this time the mutant is lacO- (an inactivating mutation in the lac operator sequence).
ANSWER: A. No change, and transcription of the lac operon will continue at a high level
lacO can be defined as the binding site for repressor. The operator deflects any repressor and transcription occurs whether lactose is around to not. Th transcription of lac operon will be carried at the same pace.
QUESTION 3: Which of the following is true for a eukaryotic gene?
Answer: A. An enhancer DNA element can influence a gene's expression in a tissue-specific manner, while the promoter DNA element is not tissue-type specific.