6.5 Gene Regulation in prokaryotes

Question 1

Prokaryotes must be able to _____ which genes are expressed at any given time

Answer 1

Regukate

Question 2

How can genes be turned on or off?

Answer 2

Based on environmental and internal cues

Question 3

What does turning a gene “on” or “off” mean? What does this allow for?

Answer 3

Whether or not transcription will take place

- cell specialization

Question 4

What are operons?

Answer 4

• a group of genes that can be turned on or off

Question 5

What are the three parts of operons?

Answer 5

• Promoter
• operator
• genes

Question 6

What is the promoter of an operon?

Answer 6

• where RNA polymerase can attach

Question 7

What is the operator of an operon?

Answer 7

The on/off switch

Question 8

What do genes do in an operon?

Answer 8

Codes for related enzymes in pathways

Question 9

Operons can be _____ or ______

Answer 9

Repressive or inducible

Question 10

What does repressible operons mean? (2)

Answer 10

• on to off

- transcription is usually in, but can be repressed, or stopped

Question 11

What does an inducible operon mean? (2)

Answer 11

• off to on

- transcription is usually off, but can be induced, or started

Question 12

What is a regulatory gene? (2)

Answer 12

• produces a repressor protein that binds to the operator to block RNA polymerase from transcribing the gene
• always exposed, but at low levels

Question 13

Is binding of a repressor to an operator reversible?

Answer 13

Yes

Question 14

The trp operon is a _____ (repressible/inducible) operon.

Answer 14

Repressible

Question 15

What does the trp operon control?

Answer 15

• controls the synthesis of tryptophan in bacteria

Question 16

What occurs in the trp operon? (3)

Answer 16

1. Since it is repressible, transcription is active
2. It can be switched off by the trp repressor
   - an Allosteric enzyme that is only active when tryptophan binds to it

Question 17

What occurs if there is too much tryptophan build up in bacteria?

Answer 17

1. Tryptophan is more likely to bind to the repressor, turning in active
2. This will temporarily shit off transcription for tryptophan

Question 18

The lac operon is an ______ operon

Answer 18

Inducible

Question 19

What does the lac operon control the synthesis of?

Answer 19

Lactase, an enzyme that digests lactose (milk sugar)

Question 20

Since the lac operon is inducible, transcription is ___

Answer 20

Off

Question 21

What is the lac repressor bound to? Which side?

Answer 21

The operator, Allosterically

Question 22

What is the inducer for the lac repressor?

Answer 22

Allolactose

Question 23

What occurs to the lac repressor when allolactose is present?

Answer 23

1. Allolactose will bind to the lac repressor and turn the lac repressor off (allosterically active)

Question 24

After the allolactose binds to the lac repressor and turns it off, what can now occur?

Answer 24

The gene can now be transcribed