Chapter 24- Regulation of Gene Expression Flashcards Preview

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Flashcards in Chapter 24- Regulation of Gene Expression Deck (42):
1

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

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)

2

How can mRNA- transcriptional level be regulated?

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

3

control of mRNA regulation in prokaryotes

controlled by regulating initiation of transcription
gene expression fluctuate in response to changing environment

4

Lifetime of prokaryotic mRNA

few minutes

5

Enzymes of prokaryotic pathway are encoding in

polycistronic mRNA, one mRNA translation produces all of the enzymes

6

control of mRNA regulation in eukaryotes

controlled by regulating transcription initiation and post-transcriptional modification stages

7

Transcription of eukaryotic genes are

monocistronic; one mRNA for one protein

8

Lifetime of eukaryotic mRNA

hours or days

9

Key regulators in prokaryotic gene expression are

the first substrate or end product

10

Negative Regulation:

regulatory protein present gene off

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

11

Positive Regulation:

regulatory protein present gene on

gene has inactive promoter, effector or activator molecule activate promoter

12

lacZ gene encodes

β-galactosidase

13

lacY gene encodes

lactose permease

14

lacA gene encodes

thiogalactoside transacetylase

15

What is the lac operon?

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

16

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

LacI repressor binds to lacO site and repress lacZYA transcription

17

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

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

18

Mutant studies proved that in lacI:

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

19

Mutant studies of LacO proved that

1. operator is required for repression
2. operator region function in cis

20

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

glucose

21

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

no induction

22

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

cAMP is low
no β-galactosidase expression

23

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

cAMP is high
β-galactosidase is expressed

24

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

decreased β-galactosidase expression

25

Glucose high, cAMP low then

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

26

If Glucose low, cAMP high then

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

27

What is purpose of Trp operon?

synthesize tryptophan

28

How is Trp operon regulated?

excess trp represses trp expression

29

What levels of regulation is involved with trp operon?

Transcriptional initiation
Feedback inhibition
Transcriptional attenuation

30

What is Transcriptional initiation?

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

31

What is Feedback inhibition?

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

32

What is Transcriptional attenuation?

Termination hairpin
Anti-termination hairpin

33

What is temporal regulation of gene expression?

Selective and sequential transcription of particular sets of genes

34

What is phage T7 major types of transcription events?

Early transcription- host sigma
Late transcription- phage RNA polymerase

35

Bacteriophage T4 has groups of genes?

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

36

Immediate-early genes (IE):

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

37

Delayed-early genes (DE):

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

38

Late genes (L):

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

39

How is the T4 genome replicated

as a rolling circle, producing extremely long concatemers

40

What unusual base does T4 contain in its DNA?

5-hydroxymethylcytosine (HMC)

41

What is bacteriophage lambda?

temperate phage

42

What lifecycle does bacteriophage lamb have?

lytic and lysogenic