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What role do insulator sequences play in the regulation of eukaryotic transcription?

A

They block communication between enhancers and nontargeted promoters
B

They block binding of transcription factors to cis-acting promoter elements
C

They block binding of transcription repressors to cis-acting promoter elements
D

They block binding of transcription factors to enhancers
E

They block binding of transcription factors to silencers

What would be the effect of a mutation in the lacI gene that prevented the repressor from binding to lactose?

A

The lac Z, Y, and A genes would not be expressed.
B

The lac Z, Y, and A genes would be expressed constitutively
C

The lac Z, Y, and A genes would be repressed by lactose.
D

The lac Z, Y, and A genes would be induced by lactose.
E

The lac Z and Y genes would be repressed but not the lac A gene.

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Reid Wolff
Reid WolffLv2
28 Sep 2019
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Related questions

1) In the wildtype (the DNA sequence most commonly found in nature) lac operon, transcription is severely down-regulated. A mutation in lacI that causes an early stop codon in the sequence (called a lacI - strain) results in an operon that has high levels of transcription of the polycistronic m-RNA. What type of regulatory protein is the LacI protein (hint: we covered this type of protein in lecture)?

The Lac regulatory protein is called a repressor. (is this correct)

2) If a bacterium with a wildtype lac operon is grown in the presence of lactose, high levels of transcription result for a while, however, eventually transcription is again down-regulated. If, on the other hand, the sugar IPTG is present (instead of lactose), transcription levels are high and remain high. What function do IPTG and lactose share? How are they differently affected by the operon product? (need help with this question)

Lactose and IPTG affected by the operon are both inducers of the Lac-Operon. (is this correct)

3) What is “epigenetics”? What forms of gene regulation are usually involved in epigenetic control of a trait? Why do we have such a limited understanding of epigenetic processes? (need help with this question)

Epigenetics is the study of phenotype changes that do not change the DNA sequence. Genes can be turned on and off based on environment situations of past generations, (parents or even grandparents) were exposed. Examples of some environmental factors could be diet, stress, smoking, drinking alcohol, and diseases. Histone modification and methylation are usually involved in epigenetic control of a trait. (is this correct)

18) In your research on gene regulation in E. coli, you produce 2 mutant strains with the same phenotype: they can grow on lactose but not on glucose. To investigate these 2 mutants further, you perform a complementation test using them and discover that the diploid combination strain can grow on glucose or lactose. From this, you can deduce that:

a.)Both mutants have a mutation in the same gene

b.)The 2 mutants have mutations in different genes
c.)Glucose and lactose metabolic pathways in E. coli utilize at least one shared gene in common
d.)At least 2 different genes are required for glucose metabolism in E. coli
e.) b) and d)

19. In your research on the lac operon, you produce a unique regulatory mutatant strain of E. Coli where the lac l gene's repressor protein binding site for the operator is normal (wild-type) but its lactose binding site no longer binds lactose. The expected phenotype of this mutant will be:

a. inability to grow on lactose only medium

b. ability to grow on lactose only medium

c. blue colony color when grown on glycerol plus x-gal medium

d. blue colony oclor when grown on lactose plus x-gal medium

e. b & d

20.

20) In your research on the lac operon, you create a diploid E.coli strain with the following genotype (+) = wild type gene, (-) = mutant gene.

I- /O+ /Z- /Y+

I+ /Oc /Z+ /Y+
Can this diploid mutant grow on medium containing lactose as the only carbon source?

a) Yes

b) No

c) Maybe, it depends on if the Oc mutation is dominant or recessive

The map of the lac operon is POZY. The promoter (P) region is thestart site of transcription through the binding of the DNApolymerase molecule before actual mRNA production. Mutationallyaltered promoters (P -) apparently cannot bind the RNA polymerasemolecule. Certain predictions can be made about the effect of P -mutations. Use your predictions and your knowledge of the lactosesystem to complete the following table. Insert a “+” where andenzyme is produced and a “-” where no enzyme is produced. The firstone has been done as an example.

ß-Galactosidase Permease
Genotype No lactose Lactose No lactose Lactose

a. I- P+ OC Z+ Y- / I+ P+ O+ Z- Y+

b. I+ P- OC Z- Y+ / I- P+ OC Z+ Y-

e. I- P+ OC Z+ Y- / I- P+ O+ Z- Y+

f. I- P- O+ Z+ Y+ / I- P+ OC Z+ Y-

Could you guys explain one of them? (a, b, e, f)



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