Tryp Operon Flashcards

1
Q

What is the Trp operon?

A

Is turned on when tryptophan isnt available from the environment

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2
Q

Enzymes trp B and A, encode what in trp operon?

A

tryptophan synthetase

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3
Q

The trp operon regulated by what?

A

Negative regulation (involves a repressor)
Attenuation (regulartion after transcriptions inititiated)

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4
Q

What is the TrpR repressor?

A

it’s the repressor in the Trp operon

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5
Q

When tryphtophan binds to the TrpR what happens?

A

the repressor binds to the operator (TrpO) and inhibit transcription of the operon

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6
Q

When does the repressor bind to the operator in the Trp operon?

A

When tryp is present in the environment

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7
Q

In the absence of tryptophan what happens to the tryp operon?

A

the repressor can’t bind so operon is on so tryptophan is synthesized

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8
Q

What is attentuation in the tryp operon?

A

is a decrease in mRNA production by a factor of 10 when tryptophan is abundant

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9
Q

When does attenuation occur?

A

after initiation of transcription

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10
Q

What is the leader sequence? How long is it?

A

In tryp operon, is 162 bp long

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11
Q

What is encoded in the leader sequence?

A

two tryps- TrpL
attenuator region
two other regions

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12
Q

What structures do mRNA leader sequences form?

A

stem-loop structures, which only have two regions form this at once

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13
Q

How does the tryp operon perform when there’s a high tryp level?

A

the leader peptide is translated by ribosome, no loop forms betwene regions 2 and 3, however 3 and 4 form a loop which causes transcription to stop after 140 bases

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14
Q

How does the tryp operon perform when there’s a low tryp level?

A

the ribosome stalls at the leader peptide cause there’s not enough tryp to make the peptide, regions 2 and 3 loop so RNA polymerase can make mrna and transcribe at the end of the leader sequence

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15
Q

What is factor independent termination in the Trp operon?

A

the 3-4 stem loop is followed by a string of U’s when transcribed, which cause termination of rna polymerase.

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