A mutant strain of E coi is found that produces both 9alactosadase and permease
ID: 198578 • Letter: A
Question
A mutant strain of E coi is found that produces both 9alactosadase and permease constitutively (Select all that apply: hint" There are two correct answers. What are the MOST likely mutations in this stra locr lacP mutation in CRP-cAMP bndng ste lacZ and lacY QUESTION 18 Which of the following genotypes produces functional lactose permease constitutively? QUESTION 19 in the lactose operon of E co, the lacp-mutation never produces the structural genes produces the structural genes only in the presence of the inducer produces the structural genes only in the absence of the inducer produces the structural genes al the time Clck Sove AS Anivers to lov. Or ve 0nd Submit to av.ro subrrExplanation / Answer
lacOc and lacI- mutation cause constitutive expression of -galactosidase and permease activity.
In Lac operon, lacOc indicates a constitutive mutation that inactivates the operator site. lacI- mutant generates no repressor molecule. At normal condition, in the absence of the inducers (allolactose), repressor protein (lacI) is produced and bind to the operator site, therefore, prevent transcription of lacZ, which encodes of -galactosidase, lacY that encodes permease and lacA encodes -galactoside transacetylase, by RNA polymerase. In the presence of lacOc mutant, as no operator site is present that can be blocked by the any present repressor molecule, so that the constitutive expression of -galactosidase, and permease occurs. In the presence of an inducer, inducer binds to the repressor molecule and causes conformational changes in the repressor, which leads to its removal from the operator site. But in the absence of the repressor molecule that is in case of lacI- mutant, operator site remains free in both the absence and presence of inducer molecule, which drives constitutive expression of -galactosidase, and permease encoding gene.
18. Question 18 is too hazy to read. The two options (III & IV) I-P+O+Z-Y+ and I-P+O+Z+Y+ genetypes are responsible for constitutive expression of permease.
In case of I-P+O+Z-Y+ genotype, only permease (no -galactosidase) is constitutively produced due to the complete absence of repressor molecule (lacI-) and the constitutive mutation of lacZ-, which encodes galactosidase. In case of I-P+O+Z+Y+, both permease and -galactosidase are constitutively produced in the absence of repressor molecule.
19. In the lactose operon in E.Coli, lacP- mutation never produces structural genes.
lacP- mutation inactivate the promoter site, where RNA Polymerase binds to transcribe the structural gene such as LacZ, LacY and LacA. Thus, in the absence of promoter site, RNA polymerase cannot transcribe the structural genes.
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