Chapter 14

Question 1

What is gene regulation

Answer 1

The level of gene expression can vary under different conditions

Question 2

What are constitutive genes

Answer 2

Genes that are unregulated and have a constant level of expression

Question 3

What is the benefit of gene regulation

Answer 3

It encodes proteins only when they are required

Question 4

How is gene expression regulated during transcription

Answer 4

Genetic regulatory proteins bind to dna and control rate of transcription
Transcription stops soon after beginning due to formation of transcriptional terminator

Question 5

What three things can stop translation from starting

Answer 5

Translational repressor proteins can bind to mRNA
Riboswitches can produce mRNA confirmation
Antisense RNA can bind to mRNA

Question 6

When else can regulation occur of gene expression in bacteria

Answer 6

When a protein undergoes post translational changes to make it a functional protein

Question 7

What does transcriptional regulation involve

Answer 7

Repressors which bind to DNA and inhibit transcription
Activators which bind to DNA and increase transcription

Question 8

What is negative and positive control in regards to regulation

Answer 8

Negative is transcriptional regulation by repressor proteins and positive control is regulation by activator proteins

Question 9

How do effector molecules affect transcription

Answer 9

They bind to regulatory proteins but not the dna directly
Also known as inducers because they can bind activators and repressors and either prevent them or cause them to bind to DNA
These genes are termed inducible

Question 10

What do corepressors and inhibitors do for transcription

Answer 10

Corepressors bind to repressors and cause effector molecules to bind to DNA
Inhibitors bind to activators and prevent effector molecules from binding
These genes are termed repressible

Question 11

When there is an inducer present what happens

Answer 11

It causes a conformational change that inhibits the ability of the repressor protein to bind to DNA and transcription proceeds

Question 12

What happens when an inducer is bound to an activator protein

Answer 12

It enables the activator protein to bind to the DNA and activate transcription

Question 13

What happens when a corepressor is bound to the repressor protein

Answer 13

Conformational change occurs that allows the repressor to bind to DNA and inhibit transcription

Question 14

What happens when an inhibitor is present

Answer 14

Causes a conformational change that inhibits the ability of the activator protein to bind to the DNA which inhibits transcription

Question 15

What is enzyme adaptation

Answer 15

Enzyme appears in the cell only after the cell has been exposed to the enzymes substrate

Question 16

What is an operon

Answer 16

Region of DNA that involves sequences that aren’t structural or expressed parts of the DNA
Consists of a few structural genes under control of one promoter

Question 17

What is a polycistronic mRNA

Answer 17

Contains coding sequence for two or more structural genes
This allows bacterium to regulate a group of genes that encode proteins with a common functional goal

Question 18

What DNA sequences operons contain

Answer 18

Promoter, terminator, structural genes, operator

Question 19

What does the lac operon and lacI gene do

Answer 19

Lac operon controls lactose metabolism
LacI gene is important for regulating the operon

Question 20

Are are the elements of a lac operon

Answer 20

Promoter which binds RNA polymerase
Operator which binds the lac repressor protein
Cap sit which binds the cap

Question 21

What are the structural genes of the lac operon

Answer 21

LacZ which encodes beta galactosidase
LacY which encodes the lactose permease
LacA which encodes galactoside transacetylase

Question 22

What are some characteristics of the lacI gene

Answer 22

Not part of lacrosse operon
Has its own promoter
Expressed at low levels and encodes the lac repressor

Question 23

What two things regulate the lac operon

Answer 23

Repressor protein
Activator protein

Question 24

What happens in the absence of inducer allolactose

Answer 24

The repressor protein is tightly bound to operator site and inhibits the ability of the rna polymerase to transcribe the operon

Question 25

What happens when allolactose is available

Answer 25

Binds to receptor and changes confirmation of repressor protein which prevents it from binding to operator site so RNA polymerase can transcribe the operon

Question 26

What happens when lactose becomes available

Answer 26

A small amount is converted to allolactose by beta galactosidase and the allolactose binds to the repressor and causes it to fall off operator site
Then lac operon proteins are synthesized which promotes efficient uptake and metabolism of lactose until lactose is depleted and allolactose levels decrease

Question 27

What is catabolite regression

Answer 27

When exposed to both lactose and glucose the E. coli uses the glucose first so catabolite regression prevents the use of lactose

Question 28

What is diauxic growth

Answer 28

The sequential use of two sugars by a bacterium

Question 29

What is cyclic amp

Answer 29

Produced from atp via adenylyl Cyclase
Binds to CAP

Question 30

What is the camp-CAP complex an example of

Answer 30

Transcriptional regulation that is inducible and under positive control

Question 31

How is the camp-CAP complex related to the lac operon

Answer 31

It binds to the CAP site near the lac promoter and increases transcription
When glucose is present adenylyl Cyclase is inhibited which decreases levels of camp so it can’t bind to CAP and transcription rate decreases

Question 32

What are the three operator sites in the lac operon

Answer 32

O1 which is next to the promoter
O2 which is downstream in the lacZ coding region
O3 which is slightly upstream of the promoter

Question 33

What must the lac repressor do to cause repression

Answer 33

Must bind to two of the three operators
Can be O1 and O2 or O1 and O3 but not O2 and 3

Question 34

What is the significance of the lac repressor binding to the two operator sites

Answer 34

The dna forms a loop which brings the operator sites closer together

Question 35

What does trpL and trpR do

Answer 35

TrpR encodes the trp repressor proteins and functions in repressing
TrpL encodes a short leader peptide and functions in attenuation

Question 36

What happens when tryptophan levels are low

Answer 36

Tryptophan doesn’t bind to trp repressor protein which prevents repressor protein from binding to operator site

Question 37

What happens when tryptophan levels are too high

Answer 37

Tryptophan acts as a corepressor that binds to trp repressor protein and tryptophan-trp repressor complex then binds to the operator site to inhibit transcription

Question 38

What happens when attenuation occurs

Answer 38

RNA is transcribed only to attenuator sequence and then transcription is terminated

Question 39

When does attenuation occur

Answer 39

In bacteria because transcription and translation are coupled
Transcription will terminate before the entire mRNA is made which is facilitated by an attenuator

Question 40

Why are two tryptophan codons found in the mRNA from the trpL gene important

Answer 40

It’s a way for bacterium to sense tryptophan levels
mRNA from trpL can form stem loops