Chapter 24- Regulation of Gene Expression

Question 1

Genes expression can be regulated at different levels. What are examples of ways to regulate gene expression?

Answer 1

1. Transcriptional level (copies of mRNA)
2. RNA post-transcriptional modification
3. Stability of mRNA (balance synthesis and degradation)
4. Translational level (rate)
5. Post-translational modification level (glycosylation, proteolytic cleavage, phosphorylation)

Question 2

How can mRNA- transcriptional level be regulated?

Answer 2

number of mRNA molecules/unit time
translation of mRNA
number of copies of a gene

Question 3

control of mRNA regulation in prokaryotes

Answer 3

controlled by regulating initiation of transcription

gene expression fluctuate in response to changing environment

Question 4

Lifetime of prokaryotic mRNA

Answer 4

few minutes

Question 5

Enzymes of prokaryotic pathway are encoding in

Answer 5

polycistronic mRNA, one mRNA translation produces all of the enzymes

Question 6

control of mRNA regulation in eukaryotes

Answer 6

controlled by regulating transcription initiation and post-transcriptional modification stages

Question 7

Transcription of eukaryotic genes are

Answer 7

monocistronic; one mRNA for one protein

Question 8

Lifetime of eukaryotic mRNA

Answer 8

hours or days

Question 9

Key regulators in prokaryotic gene expression are

Answer 9

the first substrate or end product

Question 10

Negative Regulation:

Answer 10

regulatory protein present gene off

gene has active promoter, inhibitor or repressor, keeps transcription turned “OFF”, anti-inhibitor, inducer turn the system “ON”

Question 11

Positive Regulation:

Answer 11

regulatory protein present gene on

gene has inactive promoter, effector or activator molecule activate promoter

Question 12

lacZ gene encodes

Answer 12

β-galactosidase

Question 13

lacY gene encodes

Answer 13

lactose permease

Question 14

lacA gene encodes

Answer 14

thiogalactoside transacetylase

Question 15

What is the lac operon?

Answer 15

a set of of adjacent genes transcribed as one polycistronic mRNA + the adjacent regulatory signals

Question 16

In the absence of Lactose what happens to lac operon regulation?

Answer 16

LacI repressor binds to lacO site and repress lacZYA transcription

Question 17

In the presence of Lactose what happens to lac operon regulation?

Answer 17

allolactose binds to lacI repressor causing a conformational change in the protein that prevents binding to lacO: Transcription of lacZYA genes activates

Question 18

Mutant studies proved that in lacI:

Answer 18

1. β-galactosidase expression is inducible
2. LacI is required for repression of β-galactosidase
3. LacI can compliment in trans

Question 19

Mutant studies of LacO proved that

Answer 19

1. operator is required for repression

2. operator region function in cis

Question 20

When glucose and lactose present in media what is the preferred source of carbon?

Answer 20

glucose

Question 21

If glucose and lactose present what happens to β-galactosidase expression?

Answer 21

no induction

Question 22

If glucose is high what happens to cAMP and β-galactosidase expression?

Answer 22

cAMP is low

no β-galactosidase expression

Question 23

If glucose is low what happens to cAMP and β-galactosidase expression?

Answer 23

cAMP is high

β-galactosidase is expressed

Question 24

If there are mutations in adenylate cyclase (cya) gene and cry gene (encoding CAP or CRP) what happens to β-galactosidase expression?

Answer 24

decreased β-galactosidase expression

Question 25

Glucose high, cAMP low then

Answer 25

low cAMP-CAP -> no binding to the promoter -> no activation of β−gal expression

Question 26

If Glucose low, cAMP high then

Answer 26

high cAMP-CAP -> binding to the promoter -> activation of β−gal expression

Question 27

What is purpose of Trp operon?

Answer 27

synthesize tryptophan

Question 28

How is Trp operon regulated?

Answer 28

excess trp represses trp expression

Question 29

What levels of regulation is involved with trp operon?

Answer 29

Transcriptional initiation
Feedback inhibition
Transcriptional attenuation

Question 30

What is Transcriptional initiation?

Answer 30

Trp repressor protein (trpR) binds to operator in trp operon -> repress transcription

Question 31

What is Feedback inhibition?

Answer 31

[Trp] is high, trp binds to the first enzyme in the pathway -> inactivate the enzyme, temporary shut-off of trp biosynthesis

Question 32

What is Transcriptional attenuation?

Answer 32

Termination hairpin

Anti-termination hairpin

Question 33

What is temporal regulation of gene expression?

Answer 33

Selective and sequential transcription of particular sets of genes

Question 34

What is phage T7 major types of transcription events?

Answer 34

Early transcription- host sigma

Late transcription- phage RNA polymerase

Question 35

Bacteriophage T4 has groups of genes?

Answer 35

Immediate-early genes (IE)
Delayed-early genes (DE)
Late genes (L)

Question 36

Immediate-early genes (IE):

Answer 36

use host RNAP, some IE-gene products degrade host DNA, others bind to a subunit of host RNAP, making it no longer recognize host cell promoters

Question 37

Delayed-early genes (DE):

Answer 37

modified host RNAP recognizes DE genes, T4 genome replication by DE products, one of DE products is a novel sigma factor for the late phage genes

Question 38

Late genes (L):

Answer 38

modified RNAP no longer express DE genes but transcribes L genes, synthesizing new capsid proteins, tails, and tail fibers, and assembly proteins, Finally, phage T4 lysozymes are activated

Question 39

How is the T4 genome replicated

Answer 39

as a rolling circle, producing extremely long concatemers

Question 40

What unusual base does T4 contain in its DNA?

Answer 40

5-hydroxymethylcytosine (HMC)

Question 41

What is bacteriophage lambda?

Answer 41

temperate phage

Question 42

What lifecycle does bacteriophage lamb have?

Answer 42

lytic and lysogenic