Concept explainers
a)
Interpretation: The effect on lac operon on deleting the gene encoding the lac repressor is to be determined.
Concept Introduction: E. Coli contains of lac operon, which is involved in lactose
a)
Answer to Problem 1P
In the absence of lac repressor gene, beta-galactosidase, lac permease, and thiogalactosidase transacetylase will be expressed by the cell.
Explanation of Solution
The function of lac repressor is to sense the lactose. It blocks the operon transcription in the absence of lactose. Lac operon consists of a promoter, lac repressor, terminator, lac promoter, lac operator, lac Z, lac Y, and lac A. The function of lac Z is to express beta-galactosidase, lac Y is to express beta-galactosidase permease, and lac A is to express galactosidase acetyltransferase. So, when lac repressor in gene is absent, then even in the absence of lactose, all the above proteins are expressed.
b)
Interpretation: The effect on lac operon on deleting the gene encoding the lac operator.
Concept Introduction: E. Coli contains lac operon, which is involved in lactose metabolism. It can be expressed in the presence of lactose and absence of glucose. The two regulators of lac operons are the lac repressor and the CAP. The function of these two regulators is to turn ‘on’ and ‘off’ the operon in response to glucose and lactose.
b)
Answer to Problem 1P
In the absence of lac operator gene, beta-galactosidase, beta-galactosidasepermease, and thiogalactosidase transacetylase will be expressed by the cell.
Explanation of Solution
The function of the lac operator is to express lac operon in the presence of lactose. Lac operon consists of a promoter, lac repressor, terminator, lac promoter, lac operator, lac Z, lac Y, and lac A. The function of lac Z is to express beta-galactosidase, lac Y is to express beta-galactosidase permease, and lac A is to express galactosidase acetyltransferase. So, when the lac operator gene is absent, then even in the absence of lactose, all the above proteins are expressed.
c)
Interpretation: The effect on lac operon on deleting the gene encoding the CAP.
Concept Introduction:E. Coli contains lac operon, which is involved in lactose metabolism. It can be expressed in the presence of lactose and absence of glucose. The two regulators of lac operons are the lac repressor and the CAP. The function of these two regulators is to turn ‘on’ and ‘off’ the operon in response to glucose and lactose.
c)
Answer to Problem 1P
If gene encoding CAP is absent, then even in the low glucose levels, the levels of beta-galactosidase and arabinose isomerase will remain low.
Explanation of Solution
Catabolite activator protein (CAP) senses the presence or absence of glucose. When glucose levels are low, then the operon transcription gets activated. At low glucose concentrations, cAMP is produced, which gets bind to CAP. After this, CAP binds to DNA and helps RNA pol bin to the lac operator, leading to the transcription process.
So, when the CAP gene is absent, then it cannot bind to RNA pol, and transcription of lac operator will not occur.
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