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GENE221 > Lecture 15 > Flashcards

Lecture 15 Flashcards

1
Q

What is enzyme induction?

A
  • Bacteria only produce enzymes required for growth on particular substrate in the presence of the molecule
  • It’s an efficient system as bacteria are exposed to different nutrients/conditions

-Enzyme induction is a process in which a molecule induces the expression of an enzyme.

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2
Q

What is a promotor?

A

Binds RNA Pol and initiates transcription -> mRNA

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3
Q

What is an operator?

A

Binds regulatory proteins to alter transcription

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4
Q

What is negative regulation mediated by?

A

A repressor

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5
Q

What is the role of a repressor?

A

A regulatory protein that turns off gene expression

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6
Q

How does the repressor act?

A

The repressor binds to the operator and can block the polymerase from moving past the repressor/accessing the promotor region

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7
Q

What is positive regulation mediated by?

A

An activator

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8
Q

What is the role of an activator?

A

A regulatory protein that turns on gene expression

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9
Q

How does the activator act?

A

The activator binds to the operator and assists with binding of RNA pol

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10
Q

What is the effect of a weak promotor in the absence of the activator?

A

They won’t transcribe as well

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11
Q

An inactive activator = ?

A

No expression

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12
Q

An inactive repressor = ?

A

Constitutive expression (genes keep expressing)

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13
Q

What is the repressors relation to the lac operon?

A

It controls the lac operon

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14
Q

What is the effect of an inducer?

A

A repressor would normally bind to the operator and turn off expression but if the inducer is present, this will block the repressor effect

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15
Q

The lac operon is only transcribed in the presence of …

A

Lactose

-No lactose = repressor stops expression of Lac

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16
Q

How does Lactose work in the Lac gene?

A

It is able to bind to LacI promotor as an effector, this alters its binding abilities meaning it’s unable to bind to DNA -> enabling DNA pol to express genes

17
Q

What is a polycistronic?

A

mRNA producing multiple genes

18
Q

(1. Inducers regulate new B-gal synthesis)

What is the effect of removing the inducer?

A

Synthesis of B-gal is stopped

19
Q

(2. Inducers differ from substrates)

What can other molecules that are not substrates act as?

A

Inducers

  • The component that recognises the inducer is distinct from the enzyme
  • > one recognises the inducer, one breaks down the substrate
20
Q

(3. Genes controlled together)

What did gene mapping show about the LacZ/Y/A genes?

A

That they are closely linked and co-regulated

21
Q

(4. LacI is a repressor)

What did they find about lacI-?

A
  • That they were constitutive (always on) for production of enzymes
  • They didn’t respond to inducer therefore were a regulatory mutant
  • Mapped closely to lacZYA
22
Q

What did the PajoMo experiment show?

A
  • That LacI was a repressor

- That the L+ allele was dominant

23
Q

An Fprime plasmid with a Lac+ could switch off expression in both copies of DNA. Why is this?

A

The protein is diffusible (trans)

-The lacI gene encodes a diffusible factor

24
Q

Are operator sites diffusible?

A

No, they only control the downstream gene

25
Q

What is O^C?

A

Operator Constitutive Mutants

26
Q

What mutations are dominant over repressor mutations and why?

A

Operator mutations are dominant over repressor mutations as they are downstream in the pathway
->repressor needs to bind (to DNA) to have its effect, by taking this site there’s no site to bind

27
Q

Finish the sentence

Operators are…

A

Cis acting

28
Q

What does the repressor interact with?

A

The operator

29
Q

What type of dominance does O^C have and to what?

A

O^c is cis-dominant over lacI+ and lacl^s

GENE221 (29 decks)

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