Chapter 18: Gene Expression in Bacteria

Question 1

What is the preferred energy source for E. coli always?

Answer 1

Glucose > all

Question 2

What is tryptophan in the trp operon?

Answer 2

A corepressor

Question 3

In an operon, where RNA polymerase can bind and begin transcription

Answer 3

Promoter

Question 4

How is the trp repressor activated?

Answer 4

Tryptophan binds to it

Question 5

Does the lac operon get activated when lactose is present but glucose is not low?

Answer 5

Yes, it just transcribes more slowly. Less glucose leads to faster transcription

Question 6

Usually turned off but can be switched on

Answer 6

Inducible

Question 7

How does transcription proceed in an operon?

Answer 7

When the repressor protein leaves

Question 8

In operon, can be within the promoter or between the promoter and the genes

Answer 8

Operator

Question 9

How does the E. coli cell know when to start using lactose as energy?

Answer 9

cAMP accumulates when glucose is scarce and cAMP activates CAP (catabolic activator protein) which binds to lac promoter and increases the affinity of RNA polymerase for the promoter. This increases the rate of transcription

Question 10

How is gene expression controlled?

Answer 10

Genes can be turned on and off or the level of expression can vary

Question 11

What happens in the trp operon when tryptophan is present?

Answer 11

Tryptophan binds to the repressor and activates it and can then bind to operator to block polymerase turning the operon off

Question 12

When does E. coli start to use lactose as energy?

Answer 12

When glucose is low in supply

Question 13

3 components of operons

Answer 13

Promoter, operator, and structural genes

Question 14

Set of separate genes (or operons) controlled by a single regulatory protein

Answer 14

Regulon

Question 15

What is the normal state of a lac operon?

Answer 15

Repressor (coded for by lacI) is active by itself

Question 16

Contains the genes which code for the enzymes needed to synthesize tryptophan

Answer 16

Trp operon

Question 17

Example of a regulon

Answer 17

ToxT in cholera activates many genes

Question 18

Why do bacteria need to switch genes off and on? Example?

Answer 18

Respond to changing environments. E. coli in colon synthesize tryptophan when its not in diet and don’t when it is in diet

Question 19

Usually turned on but can be inhibited

Answer 19

Repressible

Question 20

How is the trp repressor made?

Answer 20

It is coded for by the regulatory gene (trpR) which is not part of the operon

Question 21

In operon, segment of DNA that acts as the on/off switch where repressor binds

Answer 21

Operator

Question 22

What does turning genes off and on do for bacteria?

Answer 22

Makes them the most efficient

Question 23

What happens when lactose is present in a lac operon?

Answer 23

Lactose inactivates the repressor and the operon is on

Question 24

What happens in the trp operon when there is no tryptophan?

Answer 24

The trp operon is on and synthesizing tryptophan

Question 25

How is the trp operon shut off?

Answer 25

Trp repressor binds to operator to block polymerase. Occurs in the abundance of product

Question 26

What does less glucose lead to in the lac operon?

Answer 26

Less glucose leads to faster transcription

Question 27

Contains genes which code for enzymes necessary to transport and metabolize lactose

Answer 27

Lac operon

Question 28

What happens if bacteria need to coordinate a large number of genes?

Answer 28

Alternative sigma proteins and regulons

Question 29

Is the lac operon inducible or repressible?

Answer 29

Inducible

Question 30

Is the trp operon inducible or repressible?

Answer 30

Repressible

Question 31

In operon, the genes that are co-regulated

Answer 31

Structural genes

Question 32

Where can gene expression control occur?

Answer 32

Transcription, Translation, and post-translation

Question 33

What happens when there is no lactose present in a lac operon?

Answer 33

Repressor is active and bund to the operator, turning it off

Question 34

Process of converting information stored in DNA into active gene product (protein)

Answer 34

Gene expression

Question 35

Cluster of co-transcribed genes with related functions in bacteria

Answer 35

Operons

Question 36

What is the inducer in the lac operon?

Answer 36

Allolactose or lactose (substrates)

Question 37

What is needed to activate a lac operon?

Answer 37

An inducer is needed to bind and inactivate the repressor