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MOLGEN > Chapter 24 - The Operon > Flashcards

Chapter 24 - The Operon Flashcards

1
Q

Genes with related function are clustered together under the control of a single

A

promoter

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2
Q

multiple genes transcribed on a single mRNA are called

A

polycistronic

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3
Q

operon

A

Group of bacterial structural genes transcribed together
Also contains a promoter and an operator

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4
Q

structural genes

A

Multiple genes transcribed into one mRNA
Under control of one promoter

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5
Q

regulator gene

A

Under control of separate promoter
Transcribed and translated into regulator protein
Influences transcription of structural genes

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6
Q

in a negative operon, the regulator protein is a

A

repressor

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7
Q

in a negative operon the Trans-acting repressor binds to the cis-acting operator and

A

reduces the rate of transcription

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8
Q

in a positive operon the regulator protein is

A

an activator

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9
Q

in a positive operon the Trans-acting activator binds to a cis-acting element to …

A

activate transcription

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10
Q

inducible operons

A

Transcription is off by default and must be turned on (induced)

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11
Q

repressible operons

A

Transcription is on by default and must be turned off (repressed)

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12
Q

four types of operons

A

Negative inducible
Negative repressible
Positive inducible
Positive repressible

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13
Q

what kind of operon is the lac operon

A

negative inducible

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14
Q

what is the inducer in the lac operon

A

allolactose

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15
Q

lacI

A

repressor

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16
Q

lacZ

A

Beta-galactosidase

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17
Q

lacA

A

transacytylase

18
Q

lacY

A

permease

19
Q

Properties of lacI transcription

A

Unregulated gene with a low level of constitutive expression
Transcribed into a mRNA with almost no 5’-UTR

20
Q

lacOc

A

constitutive cis-acting mutation

21
Q

lacI-

A

constitutive trans-acting mutation

22
Q

lacIs

A

uninducible trans-acting mutation

23
Q

lacI-d

A

is a dominant negative trans-mutation when found in a heterozygous merozygote
One mutant subunit in the tetramer will block repressor action

24
Q

lac repressor

A

The repressor binds to an inverted repeat in the operator
Binds more tightly to the upstream side of the repeat
Within the major groove of DNA
Inducer binding changes the structure of the repressor core so that it can no longer bind into the minor groove

25
Q

three lac operators

A

lacO1
lacO2
lacO3

26
Q

lacO1

A

is the classic operator at the promoter-lacZ boundary

27
Q

lacO2

A

is 410 bp downstream of the transcription start site within lacZ

28
Q

lacO3

A

is 88 bp upstream of lacO1 within lacI

29
Q

the repressor has a higher affinity for which operator

A

O1

30
Q

each dimer on the repressor can bind to

A

a palindromic operator sequence

31
Q

When the repressor binds to O1-O2 or O1-O3, it induces a

A

loop into the DNA between the two binding sites

32
Q

Repressor binding … RNAP binding to the promoter

A

enhances

33
Q

Active repressor has … affinity for random DNA

A

low

34
Q

Almost all active repressor is bound to either

A

low-affinity sites in the genome or the operator

35
Q

Less than what percent of active repressor is free in cell

A

0.01%

36
Q

The difference in affinities between the low-affinity and high-affinity sites is large enough that

A

active repressor is usually bound to the operator

37
Q

Operator is occupied by repressor …% of the time

A

96%

38
Q

what level of transcription allows cell to always be poised for operon induction

A

basal

39
Q

When the repressor is inactivated by inducer, affinity of binding to the operator is

A

reduced

40
Q

Repressor tetramers are … on DNA

A

stored

41
Q

What are the general parameters that influence the ability of a regulator protein to bind to a specific site?

A
  1. The size of the genome dilutes the ability of a protein to bind a specific target
  2. The specificity of a protein counters the effect of genome size
  3. The amount of protein that is required for effective binding to a specific site increases with increased genome size
  4. Amount of protein must be in excess of total number of binding sites

MOLGEN (28 decks)

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