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General Biology 1 > Expression Regulation > Flashcards

Expression Regulation Flashcards

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1
Q

In what cells of your body is the lac operon?

A

None. It is in the E. Coli bacterias of your intestine only.

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2
Q

Why is the lac operon gene usually turned off?

A

It is more efficient to break down glucose than to break down lactose. However, when lactose is present and no glucose is there, the lac operon is activated to break down the lactose into glucose and galactose.

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3
Q

What are the two conditions for the lac operon gene to be expressed?

A

Glucose must be low or absent and lactose must be present

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4
Q

What is the inducer of the lac operon gene?

A

Allolactose

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5
Q

How can lactose induce the lac operon gene?

A

The lactose will bind to the repressor to change its shape and make it fall of the operator. Hence, RNA polymerase can bind to the promoter of the lac operon and transcription can proceed for the expression of the lac operon gene.

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6
Q

If the lac Operon is induced, does it necessarily proceed to expressing the lac operon gene?

A

No. Before it is induced, the lac Operon also needs to be activated by the CAP protein, which binds to the DNA to enhance transcription as if it was a transcription factor. CAP (Catabolite activator protein) is activated by attachment of the cAMP. Concentration of cAMP increases when glucose is lower. All of this is needed above from the presence of lactose, which induces the expression of lac operon by having the repressor fall of the operator.

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7
Q

What are the structural genes of the lac operon?

A

lacZ, lacY, lacA

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8
Q

What are the regulatory elements of the lac operon?

A

Plac, O, lacI

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9
Q

What is the lacZ structural gene?

A

It codes for beta-galactosidase, the enzyme required to break down lactose into glucose + galactose

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10
Q

What is the lacY structural gene?

A

It codes for permease, the enzyme that is required to bridge the environment with the cell by transporting the lactose molecules inside the cell for them to be broken down.

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11
Q

What is the lacA structural gene?

A

(Not evaluated in the course) It codes for transacetylase, which catalyzes the addition of acetyl group to many galactosides

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12
Q

What is the Plac regulatory element?

A

It is the promoter of the lac operon gene. It is the place where RNA polymerase needs to bind just before the operator.

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13
Q

What is O, the operator, regulatory element?

A

It is a sequence of DNA where the repressor protein binds to prevent the transcription of the lac operon gene. Attachment site of repressor.

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14
Q

What is the lacI regulatory element?

A

It is the gene that codes for the repressor protein, which binds to the operator and can only be removed in the presence of lactose. It is a constitutive gene, which is always expressed. The only way for it to have no effect is if lactose is present enough to have the repressor fall off.

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15
Q

What is the Pi regulatory element?

A

It is the promoter of the lacI gene. In short, it initiates the transcription of the repressor protein.

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16
Q

Is beta-galactosidase present if lactose is unavailable?

A

No. Without lactose, the repressor cannot fall off the operator and transcription is blocked.

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17
Q

Is beta-galactosidase present if lactose is available but not glucose?

A

Yes. CAP can act as help the RNA polymerase start transcription at the Plac site and lactose induces gene expression by modifying the shape of the repressor to make it fall of the operator.

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18
Q

Is beta-galactosidase present if lactose and glucose are available? Whether there is a mutation or not.

A

No. Glucose being present decreases the concentration of cAMP, which cannot activate CAP, which cannot help RNA polymerase to start transcription of the gene. Regardless of if the other genes of the operon are functional or not.

19
Q

Is beta-galactosidase present if the I gene promoter is non-functional and lactose is not available?

A

Yes. The I gene cannot code for the repressor, so it cannot block transcription even if lactose is not available.

20
Q

Is beta-galactosidase present if the I gene promoter is non-functional and lactose is available?

A

Yes. Everything happens like usual except that repressor does not fall off the operator… it was never produced!

21
Q

Is beta-galactosidase present if the repressor protein is not functional?

A

Yes. Whether lactose is there or not, if the repressor cannot block transcription of the lac operon gene, then it will be produced!

22
Q

Is beta-galactosidase present if the operon promoter is not functional?

A

NO. Whether lactose is there or not, if the promoter does not work, RNA polymerase cannot initiate the transcription of the lac operon.

23
Q

Is beta-galactosidase present if the operator is mutated?

A

Yes. Whether lactose is present of not, if the operator is not functional, the repressor cannot block transcription when lactose is not there.

24
Q

Is beta-galactosidase present if the Z gene is mutated?

A

No. The function of this gene is to produce beta-galactosidase.

25
Q

Is beta-galactosidase present if the Y gene is mutated?

A

No. Whether lactose is available or not in the environment, the Y gene cannot make permease and ensure the transport of lactose to the cell for it to act on the repressor and initiate transcription.

26
Q

Is beta-galactosidase present if the crp gene is mutated (codes for CAP)?

A

No. If CAP cannot be produced, it cannot bind near RNA polymerase to initiate transcription, regardless of if there is lactose of not.

27
Q

Is beta-galactosidase present if the CAP binding site is not functional?

A

No. If CAP cannot bind, it cannot help RNA polymerase to do the job. Hence, transcription cannot start. CAP is the activator of the Lac Operon.

28
Q

What is the difference between constitutive genes and regulated genes?

A

Constitutive genes are always transcribed and regulated genes do not always need to be transcribed to save space and energy (most of our genes).

29
Q

What are inducible genes?

A

They react to specific conditions and are thus expressed. Like lac Operon when lactose is present.

30
Q

What are temporally regulated genes?

A

Genes that are active only at certain times in the life cycle

31
Q

What are tissue specific genes?

A

They are genes that are activated in specific tissues as a result of differentiation.

32
Q

What are transcriptional regulations?

A

Regulations that affect the production of mRNA like changes in chromatin structure, DNA methylation, copying of the genes and transcription factors (enhancers, activators, repressors)

33
Q

What are post-transcriptional regulations?

A

Regulations that change the mRNA itself in the processing of pre-mRNA for example like alternative splicing and RNA interference.

34
Q

What is translational control?

A

Regulation that affects the translation process so as to modify the efficiency of the mRNA like translational repression or the adjustment of the poly-A tail.

35
Q

What is a post-translational control?

A

They are modifications to the polypeptide chain that can activate a protein like folding, removing segments (proteolytic processing), phosphorylation (remove phosphate group) and glycosylation (add sugars).

36
Q

Explain the effects of chromatin remodelling.

A

It can turn a gene on or off by allowing the RNA polymerase to reach or not the genes and find the promoter on the histones in the DNA. Euchromatin is relaxed chromatin that allows gene expression whereas heterochromatin prevents genes from being expressed.

37
Q

What does it mean to turn off a gene?

A

It means that you are silencing it, preventing proteins from being produced in the end. RNAi allows transcription, but does not allow translation to occur. Even if there is transcription, the gene is silenced.

38
Q

Explain the regulation happening with many copies of a gene.

A

When you have more copies of a gene, you can express it more and thus create some phenotypic variations. (rRNA genes produce more rRNA and the size of the brain of humans compared to the one of primates = gene DUF1220)

39
Q

Explain the regulation by transcription factors.

A

It can turn genes on or off and also increase the expression of a gene. Activators turn gene on by binding to the DNA near the promoter. They can also bind to enhancers, area near the gene. Repressors can turn genes off by binding to the promoter near the DNA.

40
Q

Explain DNA methylation.

A

It can turn a gene on or off by adding a methyl group to cytosine. Heavy methylation in the promoter region or anywhere can turn off a gene. It can be imprinted in the following generations.

41
Q

Explain alternative splicing.

A

It regulates expression by changing the outcome of the process. By cleaving different introns from the pre-mRNA alternative splicing allows for a different polypeptide chain.

42
Q

Explain RNAi (RNA interference)

A

It can turn a gene off or decrease the expression by creating a ds RNA. These cannot be translated. Small micro miRNA or siRNA binds near mRNA to prevent translation and cleave the mRNA. It may be produced in high levels of mRNA.

43
Q

Explain translational repression.

A

RNA-binding proteins attach to mRNA and decrease the rate of translation.

44
Q

Explain the adjustment of the polyA-tail.

A

If the polyA-tail is increased in length, it increases translation because it is more resistant (and vv).

General Biology 1 (17 decks)

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