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BIO3170 > Lecture 15: Transcriptional Regulation (Lac Operon, Trp Operon and Eukaryotic Transcriptional Control) > Flashcards

Lecture 15: Transcriptional Regulation (Lac Operon, Trp Operon and Eukaryotic Transcriptional Control) Flashcards

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1
Q

What is the major mechanism for controlling production of protein encoded by a gene

A

transcription

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2
Q

Fill in the blank: Transcription of a gene can be ___ or _____

A

repressed; activated

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3
Q

How is a gene repressed or activated when it comes to specifically transcription

A

repressed –> little to no mRNA synthesized
activated –> a lot of mRNA is synthesized

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4
Q

The most important process that affects protein concentrations in the cell

A

transcription

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5
Q

How are genes regulated in a single cell organism

A

–> regulated to adjust to changes in nutritional and physical environment
–> cell only produces proteins required for survival and proliferation under specific environment

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6
Q

How are genes regulated in a multicellular organism

A

–> genes are regulated to have coordination during embryonic development and tissue differentiation
–> there is diversity in transcriptional regulation and gene regulation

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6
Q

How are genes regulated in a multicellular organism

A

–> genes are regulated to have coordination during embryonic development and tissue differentiation
–> there is diversity in transcriptional regulation and gene regulation

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7
Q

What is an operon

A

a specific gene and its regulatory components

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8
Q

Fill in the blank: the lac operon encodes ___ enzymes required for the _____ of ____

A

3; catabolism; lactose

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9
Q

Fill in the blank: some organism use ___ as a food source hence the need for the lac operon

A

lactose

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10
Q

Fill in the blank: the trp operon encodes __ enzymes required for ___ of ____

A

5; biosynthesis; tryptophan

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11
Q

What is tryptophan

A

an amino acid

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12
Q

To initiate transcription in E.coli, RNA polymerase must associate with …

A

a sigma factor, most commonly sigma 70

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13
Q

Transcription of operons and isolated genes is controlled by the interactions by what three things

A

RNA polymerase and specific repressor and activator proteins

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14
Q

What are the names of the three genes in the lac operon

A

lacZ, lacY, and lacA (in that specific order read left to right in operon)

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15
Q

What are the names of the three genes in the lac operon

A

lacZ, lacY, and lacA (in that specific order read left to right in operon)

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16
Q

What are the control elements of the lac operon

A
  1. CAP site (for activator protein)
  2. Promoter
  3. Operator
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17
Q

What is an operator

A

region in gene where repressor protein can bind –> prevents RNA polymerase from binding

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18
Q

What binds on the promoter region

A

sigma factor (specifically sigma 70 for lac operon)

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19
Q

If there is a high concentration of lactose in a cell with the lac operon what is the lac repressor bound to?

A

lac repressor is bound to lactose –> if there are high concentrations of lactose in the cell you want the lac operon to be activate so enzymes that breakdown lactose (as a source of energy can be transcribed)

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20
Q

If there is a low concentration of lactose in the cell with the lac operon what is the lac repressor bound to?

A

lac repressor is bound to the operator and blocks the start site of transcription –> when there is no lactose you do not want to be breaking down any lactose you have

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21
Q

What does lacI code for in the lac operon

A

lacI –> codes for the lac repressor
note: lacI is transcribed from its own promoter

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21
Q

What does lacI code for in the lac operon

A

lacI –> codes for the lac repressor
note: lacI is transcribed from its own promoter

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22
Q

Fill in the blank: transcription of the lac operon is ___ when lactose is absent

A

repressed

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23
T or F: when there is little/ no lactose in the cell, the lac operon is bound to the promoter
F when there is little/no lactose in the cell, the lac operon is bound to the operator
24
Which operator does the lac operon bind to? What is the purpose of it binding there
--> lac repressor binds to O1 (main operator) and O2 and O3 (secondary operator --> the purpose of it binding to the operator -- prevents RNA polymerase from binding to promoter (no transcription
25
What is the active cue in a cell that lactose is present and being metabolized as a food source
allolactose
26
Fill in the blank: when lactose is present, the lac repressor binds to ____ changing ____ and releasing it from the ____ _____
allolactose; its conformation; operator sequence
27
What is the protein that lacZ encodes and what does it do
--> beta-galactosidase --> metabolize lactose into allolactose
28
Fill in the blank: when lactose is considered present it is actually ____
allolactose
29
When the lac repressor is removed from the operator what happens to the transcription of the lac operon
it is de-repressed
30
What does de-repressed mean when it comes to transcription
transcription is occurring but is happening at low levels
31
T or F: activation of an operon and de-repression are the same thing
F de-repression = transcription is occurring but is happening at low levels activation = transcription is fully functioning at normal levels
32
How is the lac operon activated?
--> after the lac repressor is removed from the operator sequence (lactose is present and it binds it allolactose) --> when glucose levels are low e.coli (prokaryote) synthesizes cAMP --> cAMP binds to and makes active CAP (a transcriptional activator protein) which in turn binds to the CAP site
33
Fill in the blank: ___ is a better energy source than lactose and other complex sugars
glucose
34
What does CAP stand for
catabolite activator protein side note: also known as CRP (cAMP receptor protein)
35
Fill in the blank: ____ interacts with RNA polymerase and greatly stimulates the rate of transcription initiation
CAP-cAMP
36
T or F: the activation of the lac operon via cAMP happens after de-repression of the lac operon
F Parallel to de-repression, the activation via cAMP occurs
37
T or F: the activation of the lac operon via cAMP happens after de-repression of the lac operon
F Parallel to de-repression, the activation via cAMP occurs
38
What are the conditions for the de-repression and activation of the lac operon
1. lactose (allolactose) is present so lac repressor is removed from operator 2. there is little glucose so cAMP can be synthesized --> binds to CAP protein and then activates operon when it binds to CAP site
39
If lactose is present and there are high glucose levels in the cell, what is the transcription level of the lac operon
low levels why? high glucose = no cAMP being produced = no activation of lac operon so the operon remains de-repressed
40
What does catabolite repression mean in the context of the lac operon
its about how the catabolites produced by the breakdown of glucose prevent production of cAMP --> high glucose = little cAMP = no binding to CAP = no activation of lac operon
41
What is a regulon
a network of operons that allows for the regulation of multiple genes in response to the environment --> these networks of operons with a common regulator --> allows coordinated shifts in cellular function that can require hundred of genes
42
Fill in the blank: ___ and ___ regulate many operons (hint: are a common regulator in a regulon)
CAP and cAMP
43
What would happen to the lac operon if: --> glucose in cell is high --> cAMP is low --> lactose is absent in the cell
--> lacI would be on and the lac repressor would be bound to the operator --> this prevents transcription of lac operon therefore there is no gene expression
43
What would happen to the lac operon if: --> glucose in cell is high --> cAMP is low --> lactose is absent in the cell
--> lacI would be on and the lac repressor would be bound to the operator --> this prevents transcription of lac operon therefore there is no gene expression
44
What would happen to the lac operon if: --> glucose is low --> cAMP is high --> lactose absent
--> since lactose is absent lacI is on and the lac repressor would be bound to the operator --> even though the cAMP-CAP complex will form and bind to the CAP site there is no de-repression --> this prevents transcription of lac operon therefore there is no gene expression
45
What would happen to the lac operon if: --> glucose is high --> cAMP is low --> lactose is present
--> the presence of lactose will lead to allolactose binding to lac repressor which leads to de-repression -- as a result the lac operon has a low level of activity/gene expression --> since glucose is present there is no need to increase expression of lac operon
45
What would happen to the lac operon if: --> glucose is high --> cAMP is low --> lactose is present
--> the presence of lactose will lead to allolactose binding to lac repressor which leads to de-repression -- as a result the lac operon has a low level of activity/gene expression --> since glucose is present there is no need to increase expression of lac operon
46
What would happen to the lac operon if: --> glucose is low --> cAMP is high --> lactose is present
--> allolactose binds to lac repressor which leads to de-repression of lac operon --> high cAMP (due to low glucose) -- cAMP binds to CAP and they both bind to CAP site on operon leading to activation of the operon --> high level of gene expression
47
Fill in the blank: the lac operon is a ___ operon and the trp operon is a ____ operon
catabolic; anabolic
48
What molecule acts as both the sensor and switch on the trp operon
tryptophan
49
Describe what happens to the trp operon when there is low tryptophan in the cell
--> when there is low tryptophan, the trp repressor is inactive --> this allows RNA polymerase to transcribe the trp genes
50
Describe what happens to the trp operon when there is high tryptophan in the cell
--> tryptophan binds to the trp repressor and activates it. As a result, transcription does not occur
51
Cell protein concentration is controlled by what four things? Which of the four contributes the most to cell protein concentration
1. Gene transcription: regulation of the frequency of mRNA synthesis 2. mRNA degradation: rate at which mRNA is degraded 3. Protein translation: rate at which mRNA is translated into protein 4. Protein degradation: rate at which a protein is degraded contributes the most --> gene transcription
51
Cell protein concentration is controlled by what four things? Which of the four contributes the most to cell protein concentration
1. Gene transcription: regulation of the frequency of mRNA synthesis 2. mRNA degradation: rate at which mRNA is degraded 3. Protein translation: rate at which mRNA is translated into protein 4. Protein degradation: rate at which a protein is degraded contributes the most --> gene transcription
52
Fill in the blank: improper regulation of mechanisms controlling transcription causes ____ _____
pathological processes
53
Dominant mutation of human HOXD13 gene leads to....
polydactyl: development of extra digits
54
Drosophila Ubx gene homozygous recessive mutations leads to ....
--> prevents Ubx expression in the third thoracic segment --> transforms the segment which usually has a halter (balancing organ) in a second copy of the thoracic segment that develops wings --> result: drosophila has two pairs of wings instead of one
54
Drosophila Ubx gene homozygous recessive mutations leads to ....
--> prevents Ubx expression in the third thoracic segment --> transforms the segment which usually has a halter (balancing organ) in a second copy of the thoracic segment that develops wings --> result: drosophila has two pairs of wings instead of one
55
What is a haltere in drosophila
a balancing organ
56
What is a transcriptional activator
--> a positive regulator --> turns genes 'on' --> frequency of transcription increases in its presence
57
What is a transcriptional repressor
--> a negative regulator --> turns genes 'off' --> frequency of transcription decreases in its presence
58
T or F: a given regulator can be an activator and a repressor
T
59
How does chromatin condensation influence gene transcription and why
--> chromatin condensation inactivate gene transcription --> why -- it blocks RNA polymerases and general transcription factors from interacting with gene
60
What are repressor proteins
--> may bind to transcription-control elements to inhibit transcription initiation by RNA Pol II --> may interact with multiprotein co-repressor complexes to condense chromatin.
61
What is a pioneer transcription factor
--> Binds to a specific regulatory sequence within the condensed chromatin. --> Interacts with chromatin-remodeling enzymes and histone acetylases that decondense the chromatin, making it accessible to RNA polymerase II and general transcription factors
62
What are activator proteins
--> Bind to specific transcription-control elements in both promoter-proximal sites and distant enhancers. --> Interact with one another and with the multisubunit Mediator complex to assemble general transcription factors and RNA polymerase II (Pol II) on promoters
63
Outline the steps the steps in eukaryotic transcriptional control
1. Repressors or pioneer transcription factors interact with the chromatin leading to a condense or more open conformation 2. repressor or activators influence the expression of genes if the chromatin is in an open conformation 3. If the activator promotes expression transcription is initiated
63
Outline the steps the steps in eukaryotic transcriptional control
1. Repressors or pioneer transcription factors interact with the chromatin leading to a condense or more open conformation 2. repressor or activators influence the expression of genes if the chromatin is in an open conformation 3. If the activator promotes expression transcription is initiated
64
What are promoter-proximal elements
--> promoter = refers to the TATA box or other sequence that recruits RNA polymerase to the transcription start site --> promoter-proximal elements are other sequences near the promoter the can regulate transcription --> promoter-proximal elements can be cell type specific

BIO3170 (5 decks)

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