3. Describe the “logic circuit” of the Lac operon. Which proteins are bound or not to DNA in each case?
a. Glucose low, lactose low.
b. Glucose high, lactose low.
c. Glucose low, lactose high.
d. Glucose high, lactose high
Lac operon is a catabolic inducible
operon.
It is expressed only in the presence of lactose provided that
glucose is absent.
Cis-elements = Promoter and operato
= Cannot be complemented
Trans-factors = Diffusible products = Ex: Repressor: Can be
complemented
In the presence of lactose, lac operon cannot bind to the operator
and hence transcription can occur.
However, glucose plays a major regulatory role to ensure that Lac
operon is not expressed in the presence of glucose.
In the presence of glucose, the adenylate cycle is inhibited. SO,
it cannot produce cAMP.
In the absence of glucose, adenylate cycle can produce cAMP which
forms an activator complex with CAP and mediates the
transcription.
a. Glucose low, lactose low.
Repressor bound at the operator
b. Glucose high, lactose low.
CAP not bound at its respective site.
Repressor bound at the operator
c. Glucose low, lactose high.
CAP bound at its respective site.
Repressor not bound at the operator
d. Glucose high, lactose high
CAP not bound at its respective site.
Repressor not bound at the operator
3. Describe the “logic circuit” of the Lac operon. Which proteins are bound or not to...
Quiz 10 1. (2 points) Which of the following conditions would lead to the highest levels of lac operon expression? a) High lactose, high glucose b) High lactose, low glucose c) Low lactose, high glucose d) Low lactose, low glucose e) None of the above would have any lac operon expression 2. (2 points) Which of the following is true concerning molecular genetics? a) tRNA carries amino acids into the nucleus in eukaryotic cells b) DNA polymerase moves towards the...
3. The CAP activator protein and the Lac repressor both control the Lac operon (see Figure 28-14). Fill out the table below with No expression, Low/Medium expression, or High expression to summarize when the Lac operon will be expressed in each of the three E. coli strains in the table. An example has been done for you. RNA polymerase- binding site (promoter) CAP binding site start site for RNA synthesis operator Lacz gene -80 -40 14080 nucleotide pairs Figure 08-14...
a) For the lac operon, will the repressor or RNA polymerase be bound to the operon in this situation? Draw what will be happening on the operon below. PROMOTER OPERATOR Lactose Enzyme 1 Lsctose Enzyme2 Lactose Enzyme 3 NO b) Will transcription occur? c) Describe what is happening (with vocabulary words). YES 2. Bobby Joe is fasting today, how will the E. coli in her stomach respond to the lack of Tryptophan? a) For the trp operon, will the repressor...
Imagine you are carrying out research on the lac
operon. You isolate six mutations in the lac operon by
measuring the amount of beta-galactosidase made in mutant cell line
under three different conditions: no lactose/no glucose; lactose
only; and lactose/glucose. Your results are shown in the table.
Strain
No Lactose, No Glucose
Lactose
Lactose, Glucose
Wild-type
None
High
Low
Mutant 1
None
None
None
Mutant 2
None
None
None
Mutant 3
None
Low
Low
Mutant 4
None
Low
Low
Mutant...
A mutation occurs in the operator of the Lac Operon. Because of this mutation, the Lac Repressor is unable to bind to the operator. If a bacterial cell contained this mutation, would the Lac operon be transcribed at a high rate (be on) or off under the following conditions: Write on or off in the blank next to each of the conditions. + glucose + lactose ________ + glucose - lactose ________ - glucose + lactose ________ - glucose -...
You have systematically mutagenized the lac operon in E. coli to produce a mutation that disrupts the function of each of the following elements: a. the promoter for LacI (P(I)) b. the LacI gene c. CRP binding site d. the promoter for the lac operon (P(lac)) e. the operator sequence f. a mutation in lacZ that disrupts the coding region but does not disrupt transcription g. a mutation in lacZ that blocks transcription For each of the above mutations, what...
In E coli the lac operon will express enzymes for the digestion of (Glucose/Lactose) when it is present, but if both the sugar mentioned before and (Glucose/ Lactose) are present the lac operon is repressed, resulting in the (Glucose/ Lactose) being used first. If there are high levels of cAMP, this means (Glucose/Lactose) levels are low, this results in a (Represser/Promoter) being activated and (Decreasing/Increasing) transcription of the lac operon.
1) The lac operon is… a) Positive repressible b) Both negative inducible and positive repressible c) Positive inducible d) Negative inducible 2) An activator regulatory protein… a) Is involved in negative regulatory control b) Is a cis acting regulatory element c) Recruits RNA polymerase to the promoter d) Prevents RNA polymerase from binding the promoter 3) For the lac operon, the presence of the substrate (lactose) activates the repressor. True or False? a) true b) false 4) cAMP… a) Activates...
5. Briefly describe positive control in the lac operon when glucose is absent and lactose is present in high amounts.
for
1-5 define those
The Lac operon is an inducible set of genes found in bacteria cells that helps the bacteria to metabolize the disaccharide lactose. When it is turned on it produces proteins that pump lactose into the bacteria cell and break it down into glucose and galactose, which can then be used by the bacteria as a source of energy The two figures below show the Lac Operon along with the lacl gene (which regulates the Lac operon...