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Principles of Genetics > Chapter 16 > Flashcards

Chapter 16 Flashcards

1
Q

When is the control of gene expression often most strongly controlled?

A

at the first step: initiation of transcrition

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2
Q

How is the initiation of transcription controlled?

A

by proteins that bind the DNA in the gene promoter
- RNA polymerase and other helping proteins bind as well

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3
Q

In E. coli, a separate regulatory gene codes for what?
Is it part of the operon it controls?

A
  • a regulatory protein
  • no
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4
Q

What is an operator?

A
  • binding site
  • when the regulatory protein binds a DNA sequence
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5
Q

Where is the operator located in relation to the promoter?

A
  • near the promoter
  • often between the promoter and the first coding region of the operon
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6
Q

What are DNA-binding proteins?

A
  • regulatory proteins
  • expressed gene will give rise to a protein
  • can bind without unwinding the DNA
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7
Q

Are DNA binding domains of each family homologous or analogous?
What about members of different families?

A

homologous
- but can evolve to bind different DNA sequences

  • only analogous
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8
Q

What are the different types of DNA-binding proteins?

A
  • Helix-turn-helix
  • Zinc finger
  • Leucine zipper
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9
Q

Define constitutive

A
  • no operators present
  • promotor is always available and functions all the time
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10
Q

What are negative inducible operons?

A
  • regulated by repressor protein (the regulatory protein is a repressor)
  • inducible: transcription is off unless turned on
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11
Q

Negative inducible operons:
How is transcription turned on?

A
  • by a small molecule (inducer)
    • binds to the repressor and turns it off
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12
Q

In inducible operons, the lack of what allows gene to be transcribed?

A

repressor

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13
Q

What are negative repressible operons?

A
  • regulated by a repressor protein
  • repressible: transcription is on unless turned off
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14
Q

Negative repressible operons:
How is transcription turned off?

A
  • by a small molecule (corepressor)
    • binds to the repressor and turns it on
  • repressor can now bind to the operator and inactivate the gene
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15
Q

in repressible operons, what must be present in order to turn off gene transcription?

A

active repressor

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16
Q

What is a positive control?

A

When the regulatory protein that binds is an activator
- increases transcription

17
Q

What is positive inducible?

A
  • transcription is off
    • activator protein is inactive unless binded to an inducer
18
Q

What is positive repressible?

A
  • Transcription is on
    • activator protein is active unless binded to a small molecule that inactivates it
      • represses the operon
19
Q

The Lac operon allows E. coli to use what as a carbon and energy source?

A

lactose (milk sugar)

20
Q

Regulation of the lac operon: Is it on or off when there is…
Glucose only?
Glucose and lactose?
Lactose only?
Neither?

A
  • nearly turned off
  • nearly turned off
  • turned on
  • nearly turned off
21
Q

The lac operon contains how many cistorns ( protein coding regions)?
What are they?

A

3

  • lac Z
  • lac Y
  • lac A
22
Q

What is the lac Z cistron?

A
  • codes for (beta)-galactosidase
  • breaks lactose into glucose and galactose
  • converts some lactose into allolactose
    • breaks up into glucose and galactose
23
Q

What is the lac Y cistron?

A
  • lactose permease
  • cell membrane transported for lactose
  • even with the lac operon off, there is still enough to allow a low level of lactose in
24
Q

lac Y cistron:
Even with the lac operon off, there is still enough to allow a low level of lactose in.
Why is this important?

A

The cell has to be able to detect that lactose is present

25
Q

What is the lac A cistron?

A
  • transecetylase
  • acetylates lactos-related substrates
  • not need for lastose metabolism, but gives E. coli an advantage in the presence of non-metabolizable lactose analogs
26
Q

What are analogs?

A

a molecule similar to another molecule

27
Q

Lac operon:
Define when it is positive inducible

A

CAP activates the operon in the absence of glucose

28
Q

Lac operon:
Define when it is negative inducible

A

the lac repressor inactivates the operon in the absence of lactose

29
Q

Positive inducible control of the lac operon by CAP:
Most cellular organisms can convert ATP into what?
What type of molecule is it?

A
  • cyclic AMP (cAMP)
  • signaling molecule
30
Q

In E. coli, cAMP level are what in relation to glucose levels?

A

reversely proportional

31
Q

lac operon/positive inducible:
How is CAP activated?
What is its un-abreviated name?

A
  • cAMP bind to it
  • catabolite activator protein
32
Q

lac operon/positive inducible:
How does the lac operon become active?

A
  • when the active CAP activates it
    • binding upstream from the promoter and recruiting RNA polymerase
33
Q

Lac operon/negative inducible:
The lac operon is coded by what?

A
  • the lac I locus
    • has its own constitutive promoter (not part of the lac operon)
34
Q

Lac operon/negative inducible:
In the absence of lactose, the lac repressor binds to what of the lac operon?
What happens afterwards?

A
  • operator
  • blocks RNA polymerase
35
Q

Where is the operator located in the lac operon?

A

between the promoter and the first coding region

36
Q

Lac operon/negative inducible:
binding of the lac repressor to the operator is what type of process?
What does this mean?

A
  • equilibrium process
  • the operator isn’t constantly bound
37
Q

Lac operon/negative inducible:
In the presence of lactose what converts some lactose into allolactose?
What does the allolactose do?

A
  • (beta)-galactosidase
  • binds to the lac repressor and prevents it from binding
38
Q

Lac operon:
Is the lac operon on or off, and is the CAP and lac repressor active or inactive when there is…
Glucose only?
Glucose and lactose?
Lactose only?
Neither?

A
  • lac operon: nearly off, CAP: inactive, Lac repressor: ACTIVE
  • lac operon: nearly off, CAP: inactive, Lac repressor: inactive
  • lac operon: nearly ON, CAP: ACTIVE, Lac repressor: inactive
  • lac operon: nearly off, CAP: ACTIVE, Lac repressor: ACTIVE
39
Q

Does the cell favor lactose or glucose?

A

glucose

Principles of Genetics (11 decks)

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