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Regulation of Gene Expression > Regulation of Gene Expression > Flashcards

Regulation of Gene Expression Flashcards

1
Q

What are inducible genes? What are repressible genes?

A

Inducible genes: genes that are normally OFF; can be turned ON

Repressible genes; genes that are normally ON; can be turned OFF

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2
Q

What are constitutive genes?

A

“House-keeping” genes that are more or less constant.

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3
Q

What levels of control are there?

A

Transcriptional and Translational

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4
Q

How are the 1000-fold differences in mRNA product of constitutive genes accounted for?

A

Differences in promoter sequence.

NOTE: If the consensus sequence the promoters are a part of deviate from the norm too much, promoter function is reduced.

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5
Q

List the regulation factor types and their mechanism of action.

A

Specificity: Alter the RNA Polymerase’s specificity for promoter sequences. (Bacteria - sigma factors; Eukaryotes - TBP Protein)

Repressor: block RNA pol from attaching to promoter (aka negative regulation)

Activator: enhance RNA pol-promoter interaction (aka positive regulation)

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6
Q

What two regions do different sigma factors recognize on different sequences?

A

-10 and -35

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7
Q

What are the signal molecules that act on repressors?

A

Co-repressor: enhances binding of repressor to operator

inducer: reduces binding of repressor to operator

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8
Q

What are the signal molecules that act on activators?

A

Co-activator: enhances binding of activator to promoter

repressor: reduces binding of activator to promoter

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9
Q

What are operons? What are some examples?

A

A promoter region found only in bacteria that contains a binding site for RNA Polymerase as well as neighboring binding sites for activators and repressors.

Ex. trp operon, lac operon

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10
Q

What are the products of operons?

A

polycistronic mRNA

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11
Q

What are the gene components of the lac operon?

A

lacZ - codes for beta-galactosidase
lacY - codes for lactose permease
lacI - codes for constitutively expressed repressor

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12
Q

How does allolactose participate in the lac operon?

A

It is an inducer; it binds to the repressor and pulls it off of the operon.

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13
Q

What does the lac operon need to function?

A

CRP (cAMP Responsive Protein) aka CAP (Catabolite Activator Protein)

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14
Q

What does CRP/CAP require to function? (it’s in the name)

A

cAMP

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15
Q

List the effects of glucose AND lactose on the lac operon.

A

If glucose is in the cell, lac operon will not function, regardless of whether lactose is present or not. Glucose inhibits adenylyl cyclase, preventing cAMP from binding to CRP/CAP.

If lactose (or allolactose) is present and glucose is not, lactose will remove the lac repressor and CRP/CAP will bind to the lac operon, activating it. (THIS IS THE ONLY CONDITION UNDER WHICH THE LAC OPERON IS ACTIVATED)

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16
Q

What is the regulation of the trp operon?

A

A 15 bp region that acts as a repressor for the operon.

17
Q

What is required for the effective regulation of the trp operon?

A

2 trp molecules act as co-repressors. The repressor will not bind as effectively to the operator without the trp molecules.

18
Q

How much does a high concentration of tryptophan affect the expression of the trp operon?

A

Reduced by a factor of 70

19
Q

What is the total reduction of expression if attenuation is taken into account?

A

700-fold

20
Q

in eukaryotic genes, how many regulatory sites are there, and where are they located?

A

5 regulatory sites; 1000s of bp upstream/downstream of TX site

21
Q

What is attenuation? What is the attenuator structure?

A

The inhibition of gene expression via premature termination.

The 3:4 hairpin loop.

22
Q

When does attenuation occur in the expression of the trp operon? What is the mechanism of expression in relation to trp?

A

Attenuation occurs when the concentration of tryptophan in the cell is high. There are 2 trp slots on the leader sequence, and the concentration of trp in the cell will affect how quickly the ribosome will be able to advance on the mRNA, which will determine whether attenuation occurs or not.

23
Q

What are the structures formed by the trp operon with or without attenuation?

A

Without attenuation (low trp concentration): 2:3 hairpin loop

With attenuation (high trp concentration: 3:4 hairpin loop.

24
Q

What are the 2 types of chromatin-remodeling enzymes? What are the enzymes of each category?

A

Core histone modifiers: HATs and HDACs

nucleosome remodelers/repositioners/removers: SWI/SNF complexes

25
Q

What are some diseases caused by mutation to chromatin-remodeling enzymes?

A

Rubinstein-Taybi Syndrome - mutation in proteins with HAT activity

OMIM - mutation in protein in SWI/SNF family

26
Q

What are the functions of the histone core modifiers?

A

HATs - Histone Acetyl Transferases: add acetyl groups to H3 and H4 to encourage histone to open up, allowing transcription to take place.

HDACs - Histone Deacetylases

27
Q

What are cis-acting genes? What are examples of cis-acting genes?

A

Regulatory elements the are on the same chromosome as the transcribed gene.

Enhancers and Insulators.

28
Q

What are trans-acting genes?

A

Genes that code for Activator/Repressor genes that diffuse to site of action.

Note: cis-acting enhancers 1000s of bps away from TX start site will act on the initiation complex via DNA looping and trans-acting activator proteins.

29
Q

What is the function of an insulator?

A

Limits the action range of enhancers. If the insulator element lies between the enhancer and the target gene, the target gene will not be expressed.

30
Q

Explain what a barrier sequence is.

A

A sequence that stops heterochromatin from ‘spreading’ back into the active site of transcription.

31
Q

List the requirements for RNA Pol II to bind to a promoter.

A
  1. Basal transcription factors (TFIIX)
  2. DNA-binding transactivators that bind to enhancers
  3. Co-activators that act indirectly: bridge gap between DNA-binding transactivators and Pol II complex
32
Q

What are examples of co-activators that assist in RNA Pol II binding to a promoter? What remodeling attribute do many of them have?

A

TFIID, Mediator

Many co-activators have HAT activity or bind to acetylated Lys residues.

Regulation of Gene Expression (1 decks)

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