For the E. coli lac operon, write the partial diploid genotype (for O,Z and Y) f
ID: 68831 • Letter: F
Question
For the E. coli lac operon, write the partial diploid genotype (for O,Z and Y) for a bacterial strain with an F prime plasmid that will produce beta-galactosidase constitutively and permease inducibly. Assume that the recipient carries a wild-type I+ gene and that the F prime carries the wild-type O+ and no copy of the I gene. Use the following symbols exactly as shown for the genetic elements (O is "oh" not "zero": O+, O(c), Z+, Z-, Y+, Y-. Your answer should be a string of symbols in the order OZY. First describe the endogenote (recipient genotype), next describe the exogenote (F prime). (e.g. O+Z+Y+)
20-a. [1pt]
The endogenote:
Answer:
20-b. [1pt]
The exogenote:
Answer:
20-c. [3pt]
You have recovered a strain of E. coli with a null mutation of the gene for catabolite activator protein (CAP). Which of the following do you expect to be true regarding the expression of a completely wild-type operon? If the first two are true and the remainder false, enter TTFFFF.
Both beta-gal and permease will be made constitutively.
CAP protein will be bound irreversibly to the lac promoter.
Other operons coding for enzymes of degradative pathways for other sugars (e.g. maltose, arabinose, etc.) will be effectively non-inducible?
The lac repressor will be unable to bind to the operator when lactose is absent.
The lac repressor will be unable to bind to the operator when lactose is present.
cAMP alone will bind to the CAP binding site at the lac promoter.
Answer:
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Explanation / Answer
1.The partial diploid genotype for a bacterial strain with an F prime plasmid that will produce beta-galactosidase constitutively and permease inducibly is :
I+ Oc Z+ Y- /I-O+ Z+ Y+
2. During low concentration of glucose, cAMP levels increase in the cell. This activates catabolite activator protein ( CAP, a transcriptional activator) bind to cAMP to induce transcription of lac operon. CAP induce transcription of lac operon in absence of glucose. For the expression of lac operon glucose must be in low concentration and lactose must be present, since lactose is converted to glucose and galactose by beta galactosidase.
a.Both beta-gal and permease will be made constitutively.
CAP protein will be bound irreversibly to the lac promoter.
b
c.
d. False. When lactose is absent, expression of lac operon donot occur as lactose couldnot bind to repressor to prevent transcription.
e. True. When lactose is present in the cell, it binds to repressor , then repressor cannot bind to operator. RNA polymerase binds to promoter and lac operon expression occurs.
f. False . cAMP donot bind to CAP binding site of promoter.