The following table lists several genotypes associated with the lac operon in E.

Question

The following table lists several genotypes associated with the lac operon in E. coli. For each, indicate with a "+" or a "-" whether ?-galactosidase would be expected to be produced at induced levels. (Assume that glucose is not present in the medium.)

I+ = wild-type repressor
I- = mutant repressor (unable to bind to the operator)
Is = mutant repressor (insensitive to lactose)
O+ = wild-type operator
Oc = constitutive operator (insensitive to repressor)

For the genotype,

which of the following should be entered into the chart?

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Part B

For the genotype,

which of the following should be entered into the chart?For the genotype,

which of the following should be entered into the chart?

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Part C

For the genotype,

which of the following should be entered into the chart?For the genotype,

which of the following should be entered into the chart?

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Part D

For the genotype,

which of the following should be entered into the chart?For the genotype,

which of the following should be entered into the chart?

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Genotype No Lactose Lactose I + O+ Z+/ F' I - O+ Z+ I - Oc Z+/ F'I - O+ Z- I s Oc Z+/ F'I + O+ Z+ I - O+ Z+/ F' I - O+ Z+

Explanation / Answer

LAC OPERON;

LACTOSE OPERON ,IS A REQUIRED FOR THE TRANSPORT AND METABOLISM OF LACTOSE IN E.COLI.

LAC OPERON CONSISTS OF 3GENES ,The lac operon consists of three structural gene, and a promoter a terminator , regulator, and an operator.. The three structural genes are: lacZ, lacY, and lacA.

LAC OPERON MAKES PROTIENS ONLY IF THE LACTOSE IS AVILABLE IE., SUBSTRATE

LacI mutants areconstitutive, meaning that they always express ?galactosidase at high levels regardlessof whether there is an inducer present or not.LacILacILacI mutants have apparently lost acomponent of the machinery the cell uses to turn off ?galactosidase expression.{ LAC i IS INDUCED MUTANT}. I- AND Oc is a mutnants .

ANSWER ;

GENOTYPE; I + O+ Z+/ F' I - O+ Z+ ,

-,+  beta gal is made w hen there is lactose

GENOTYPE; I - Oc Z+/ F'I - O+ Z-

+ ,+ WHERE THE beta -GAL IS MADE ALL THE TIME , BACAUSE THE OPERATOR CANNOT BIND TO REPRESSOR ,AS THERE IS MUTATION IN THE OPERATOR GENE.

GENOTYPE; I s Oc Z+/ F'I + O+ Z+

-, -  where the gene is regulated

GENOTYPE ;I - O+ Z+/ F' I - O+ Z+

-,+,WHERE OPERATOR IS PRESENT.

Genotype No Lactose Lactose I + O+ Z+/ F' I - O+ Z+ -    + I - Oc Z+/ F'I - O+ Z-    +     + I s Oc Z+/ F'I + O+ Z+    -    -                I - O+ Z+/ F' I - O+ Z+      -    +

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