Bio midterm 2 Lac Operon notes

are glucose and lactose levels high or unavailable in this scenario?

Glucose is unavailable, Lactose is high

are glucose and lactose levels high or unavailable in this scenario?

Glucose is high, Lactose is unavailable

are glucose and lactose levels high or unavailable in this scenario?

glucose is unavailable, lactose is unavailable

are glucose and lactose levels high or unavailable in this scenario?

Glucose is high, lactose is high

For ecoli transcription the wild type is given glucose how does that effect the ara operon and the lac operon transcription

Glucose decreases AC which decreases cAMP which in turn means that the ara and lac operon will not transcribed

For ecoli transcription the wild type is given glucose and cAMP; how does that effect the ara operon and the lac operon transcription

cAMP activates both the lac and ara operon

For ecoli transcription the cya- phenotype is given cAMP how does that effect the ara operon and the lac operon transcription

cya- doesnt have AC so glycose is down and the lac and ara operon are trascribed

In a LacI⁺ / LacI⁻ merodiploid strain (one chromosome has LacI⁺, the other LacI⁻), lactose is absent — will the lac structural genes be repressed or constitutively expressed?

The structural genes will be repressed, because its a transacting gene so the lacI+ works for both strains and the gene will be repressed

In E. coli, if glucose is low and lactose is high, what happens to cAMP levels and how does that affect lac operon expression? What enzyme would you expect to be produced in high quantities?

cAMP will be high which will cause the lac operon to be on and create beta galactosidase

An E. coli cell is given both glucose and lactose. A researcher then adds exogenous cAMP to the culture. How does beta-galactosidase production change compared to the cell without added cAMP, and why?

The cAMP would could for the CAP protein and cause the lac operon to be on and create beta galactosidase

A mutation results in a LacI⁻ genotype. How does this affect lac operon transcription when lactose is absent, and is this mutation cis-acting or trans-acting?

LacI- means that the lac operon will be on nomatter what, so a lack of lactose doesnt effect the lac operon transcription and it is Transacting

Compare the roles of LacZ, LacY, and LacA in lactose metabolism. Which two are considered the primary structural genes?

LacY and Lac Z are the primary structural genes because they incode for beta galactosidase in lac z and in lac y they incode for lactose permease which is the primary structure of the gene, Lac A incodes for an enzyme that gets rid of the waste which isnt apart of the primary structure of the gene.

A LacOᶜ mutation is introduced into an E. coli cell. How does this affect transcription of the structural genes regardless of lactose levels, and why can't a second wild-type operator on another DNA strand rescue this phenotype?

LacOᶜ mutation means that the operator cant bind to the resistor, which means that lac operon is constantly expressed, the mutation is also cis so it cannot change strands

What is the difference between a constitutive and inducible mutation in the context of the lac operon?

constitutive mutations means that the lac operon is always on, inducible means that the lac operon can be turned on or off depending on the amount of lactose in the system

A wild-type E. coli cell has glucose present and lactose absent. Predict the level of beta-galactosidase produced?

very little to no beta galactosidase produced

On e coli mutants which result in uniducible phenotype for beta galactosidase

Lac Z-: cant produce beta galactosidase so the amount of beta galactosidase doesnt change with the amount of lactose, LacY-: same thing as before it stops lactose from entering the cell so it cannot be induced, LacI^S the reducer is always on so its not inducible

In ecoli the genotype of the chromosome is lacZ- and lacI- and the genotype of the F’ plasmid is LacZ+ LacI+ is beta galactosidase inducible, uninducible or constitutive?

Inducible: LacZ and lacI are transacting so they will lead to a wildtype phenotype and thus make it inducible

In ecoli the genotype of the chromosome is lacZ- and lacI- and the genotype of the F’ plasmid is LacZ+ LacI^S is beta galactosidase inducible, uninducible or constitutive?

Uninducible: The LacI^S means that the reducer is always on

In ecoli the genotype of the chromosome is lacZ- and lacI- and the genotype of the F’ plasmid is LacZ+ LacI- is beta galactosidase inducible, uninducible or constitutive?

Constitutive: The lac I which codes for the repressor is always off, so it is constitutive

In ecoli the genotype of the chromosome is lacZ- and lacI- and the genotype of the F’ plasmid is O^C LacZ+ LacI+ is beta galactosidase inducible, uninducible or constitutive?

constitutive: O^C means that the repressor cant bind to operator, which means that the gene is always being transcribed for

In ecoli the genotype of the chromosome is lacZ+ and lacI+ and the genotype of the F’ plasmid is none, is beta galactosidase inducible, uninducible or constitutive?

Inducible: This is the wildtype phenotype

In ecoli the genotype of the chromosome is lacZ+ and lacI+ and the genotype of the F’ plasmid is LacZ+ LacI+ is beta galactosidase inducible, uninducible or constitutive?

Inducible: wildtype phenotype

In ecoli the genotype of the chromosome is lacZ+ and lacI+ and the genotype of the F’ plasmid is LacZ+ LacI^S is beta galactosidase inducible, uninducible or constitutive?

Uninducible: The LacI^S means that the reducer is always on

In ecoli the genotype of the chromosome is lacZ+ and lacI+ and the genotype of the F’ plasmid is LacZ+ LacI- is beta galactosidase inducible, uninducible or constitutive?

inducible: lacI+ is transacting so they will lead to a wildtype phenotype and thus make it inducible

In ecoli the genotype of the chromosome is lacZ+ and lacI+ and the genotype of the F’ plasmid is LacZ+ LacI+,O^c is beta galactosidase inducible, uninducible or constitutive?

constitutive: O^C means that the repressor cant bind to operator, which means that the gene is always being transcribed for