Biology 1002B Lecture Notes - Lecture 17: Nuclear Membrane, Dicer, Rna Interference

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periwinklefrog466

12 Apr 2017

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X-gal is a substrate with galactoside bond that, when cut by galactosidease, turns the cell blue. Xgal is transported across the cell membrane the same way that lactose is but it does not bind the lac repressor. Assume you have a mutant that is deleted for the entire lac operator. What color will your cells be when grown in xgal and glucose: white (no blue, light blue, dark blue. If galactosidease is present, it will digest glucose and make the cell turn blue ( a lot of galactosidease= more blue) Mutant will make galactosidease: no operator, so no place for repressor to bind- no way to stop transcription, therefore will make lots of galactosidease (more blue) However there is glucose: decreases expression of operon. Deleting operator won"t turn it off- it leaves it on. Implications of having message protected in nucleus allows more regulation control.

Related Questions

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

salmonporpoise696

For this question, focus on four parts:

I, the gene that produces the repressor protein;

P, the promoter region where RNA polymerase binds to initiate transcription;

O, the Operator site, where the repressor binds. When the repressor binds, it prevents transcription; and

ZYA, the three structural genes, all of which are required for the successful utilization of lactose as a food source.

In the left column of the table below, we indicate the genetic composition at the lac operon of particular strains of E. coli cells. A "+" (plus sign) following the letter indicates the wild-type allele (or normally functioning version of the gene). For I, P, and ZYA, a "-" (negative sign) following the letter indicates the mutant allele (or non-functional version of the gene). For the O allele, a "C" indicates the mutant or constitutive allele. It is not functional in that the repressor cannot bind, but it is functional in that transcription can still occur.

Given the conditions stated in each column, please indicate for each genotype whether lac mRNA is produced and at what level by typing in one of the following words in each cell in the table:

"Abundant"

"Minimal"

"None"

The completely wild-type genotype has already been filled in.

	Cellular conditions:
Genotype	Glucose present (low cAMP) and no lactose	Glucose present (low cAMP) and lactose present	No glucose (high cAMP) and lactose present
*I⁺ P⁺ O⁺ ZYA⁺*	None	Minimal	Abundant
*I^- P⁺ O⁺ ZYA⁺*
*I⁺ P^- O⁺ ZYA⁺*
*I⁺ P⁺ O^c ZYA⁺*
*I⁺ P⁺ O⁺ ZYA^-*

champagneyak301

Are my answers correct?

1. 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?

Lactose and IPTG are both inducers of the Lac-Operon. Lactose is a substance that the enzyme will react with (substrate), which is split or cleaved by the Beta-galactosidase. When you add lactose expressions level of lac operon will increase but as lactose is used by the beta-galactosidase expression levels of lac operon will decrease.

IPTG is a chemical cannot be split or cleaved by beta-galactosidase. The expression level of lac operon will remain the same.

Or Lactose can be easily broken down but IPTG cannot be broken down. What does expressions level mean?

2. If a lacI - bacterium is grown in the presence of the sugar X-gal, a blue dye appears; however, the concentration of X-gal decreases over time. What has happened to the X-gal?

If a lacI - bacterium is grown in the presence of the sugar X-gal, the Lacl is mutant or the gene is damaged which alters the genetic message carried by that gene. The LacI gene produces the repressor protein which switches off the operon, but since it is damaged no repressor protein is produced and the operon is switched on. The Lacl is transcribed into beta-galactosidase (lactose) The enzyme beta-galactosidase (lactose) splits or separates the X-gal which will result in decreased concentration of X-gal with time.

3. If a wildtype bacterium is grown in the presence of the sugar X-gal, transcription of the polycistronic m-RNA does not occur. What is X-gal unable to do? Without adding lactose (or genetically modifying the bacteria), how could you fix this problem

X-gal cannot form lactose, the repressor remains off and beta-galactosidase is not formed. This can be fixed by adding IPTG which can switch on the operon

Biology 1002B Lecture Notes - Lecture 17: Nuclear Membrane, Dicer, Rna Interference

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