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Genes > Phage Lambda > Flashcards

Phage Lambda Flashcards

1
Q

Define lytic cycle

A

Virus infects a host cell
Replicates
Destroys the cell to release newly formed viral particles

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2
Q

Define lysogeny

A

Viral genome integrates into the host cell’s genome
Replicates alongside it without causing immediate lysis

In this state, the viral DNA/RNA is known as a PROPHAGE when integrated into the host genome

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3
Q

What state are viral genes integrated in lysogeny?

A

Genes are transcriptionally silent or express only a few genes = allowing the virus to persist in the host without causing immediate harm

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4
Q

Define prophage

A

A phage genome covalently integrated into a bacterial genome

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5
Q

Define phage immunity

A

The ability of a prophage to prevent another phage of the same type from infecting a cell

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6
Q

What does induction of a phage mean?

A

Under certain condition, the prophage can be induced to exit the lysogenic state and enter lytic cycle

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7
Q

What happens to viral gene expression in induction?

A

Phage DNA is released and enters the lytic cycle

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8
Q

Why may induction of a phage occur?

A

Destruction of a lysogenic repressor
Environmental stress
Changes in host cell

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9
Q

What can a temperate phage do?

A

Can choose between lytic and lysogenic pathway development

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10
Q

What can a virulent phage do?

A

Lytic phage = cannot display lysogenic cycle

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11
Q

What are the periods of lytic development?

A

Early period = before replication
Late period = after replication onset

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12
Q

What are phage genomes and protein particles first assembled into in lytic development?

A

Progeny phages

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13
Q

What are the two early genes?

A

cro = negative regulator
N = antiterminator

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14
Q

What is N gene required for?

A

Expression of delayed early genes

N = synthesizes delayed early genes

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15
Q

What are the 3 delayed early genes?

A

Regulators = cii, ciii, Q

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16
Q

What delayed early genes does lysogeny require?

A

cii and ciii

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17
Q

What genes does the lytic cycle require?

A

cro = early gene
Q = delayed early gene

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18
Q

What genes does the lysogenic cycle not have?

A

Late genes

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19
Q

What order does the lambda repressor bind operators?

A

O1-2-3

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20
Q

What is the outcome of lambda repressor binding operator?

A

Represses expression of lytic genes

Maintains lysogenic cycle

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21
Q

What is the role of cro?

A

Promotes lytic cycle
Prevents lambda repressor from binding

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22
Q

What promoters are the early genes transcribed by?

A

N = promotor L
cro = promoter R

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23
Q

What is the role of the anti-terminator protein? (pN)

A

Allows RNA polymerase to pass the terminators = tL1 tR1

24
Q

What does N mRNA code for?

A

N protein

25
Q

What is the role of Q protein?

A

Anti-terminator = allows RNA polymerase to transcribe the late genes for the LYTIC cycle

26
Q

What happens to the lambda DNA after infection?

A

It circularizes = late genes form a single transcription unit

27
Q

What is the late genes’ promoter called?

A

PR’

28
Q

What gene encodes lambda repressorand what are its promoters?

A

cl gene
PRM = promoter right maintenance
PRE = promotor right establishment

29
Q

What genes does lambda repressor block from being transcribed?

A

N and cro
Lambda repressor acts at operators = blocking transcription of immediate early genes

30
Q

How is transcription of cl stimulated?

A

Lambda repressor binding at operator R = stimulates transcription of cl from PRM

31
Q

What is the structure of the lambda repressor?

A

Monomer has two domains
NTD = DNA binding site
CTD = dimerization

32
Q

What is required for lambda repressor to bind DNA?

A

Must be a dimer

33
Q

How is the lytic cycle induced?

A

Cleavage of the repressor between the two domains = reduces affinity to operators
Inducing the lytic cycle

Cleavage can occur because of UV or temperature

34
Q

How does lambda repressor bind DNA?

A

Helix-turn-helix motif = arrangement of two alpha-helices that bind DNA

35
Q

What is the role of the recognition helix?

A

Lambda repressor recognition helix (helix 3) = recognizes operator sequence in phage genome

FIts into major groove

36
Q

Describe the lambda operator sequence

A

17 bp sequence
Axis of symmetry through central base pair

37
Q

Phage immunity occur between phages with the same what?

A

Immunity region

38
Q

What happens in virulent mutations?

A

Unable to establish lysogeny because mutation in operator but repressor cannot bind

39
Q

What is serial dilution used for?

A

To count phage

40
Q

What is a plaque?

A

Hole in a bacterial lawn

41
Q

What are the different plaque morphologies seen?

A

Wild-type phages = cloudy plaques
Because they contain some cells that have established lysogeny instead of being lysed

Virulent mutants = clear plaques
Because unable to establish lysogeny so the plaques only have lysed cells

42
Q

What two regions overlap?

A

Operators overlap with promoters

43
Q

How does the lambda repressors’ autoregulatory circuit work?

A

DNA-binding region of repressor at OR2 contacts RNAp and stabilizes its binding to PRM = promotes cl synthesis

Repressor blocks N and cro transcription = blocks entry into lytic cycle

44
Q

Where is the DNA-binding region found in lambda repressor?

A

Helix 2

45
Q

What does cooperative interaction increase?

A

Sensitivity of regulation

46
Q

Cooperative ???

A
47
Q

Why are cII and cIII genes needed to establish lysogeny?

A

These delayed early genes are need for RNAp to initiate transcription at PRE
cIII = protects cII from degradation
Transcription from PRE = synthesis of repressor and blocks cro synthesis

48
Q

What is the role of cII protein?

A

RNAp only binds promoter in presence of cII

49
Q

What is the role of cIII protein?

A

Protect cII from degredation

50
Q

Why can transcription from PRE block cro synthesis?

A

…?

51
Q

Where does cII act at?

A

PRE

52
Q

What are the steps in lysogeny?

A

Immediate early genes N and cro are transcribed
N protein antiterminates allowing delayed early genes to be transcribed = cII and cIII
cII acts at PRE = cl is transcribed
Establishment of repressor turns off early gene expression
Repressor binds OR and OL
cl is transcribed from PRM

53
Q

What are the steps in teh lytic cycle?

A

N and cro are transcribed
N antiterminates, allowing delayed early genes to be transcribed = cII and cIII
cro binds O3-2-1 affinity
Binding OR3 = prevents RNAp binding PRM
Cro represses immediate early genes = indirectly blocking repressor establishment
pQ activates late expression

54
Q

What is the same between the lytic cycle and lysogeny?

A

Delayed early stage = both Cro and repressor are being expressed

55
Q

What is deteremines which cycle the phage goes through?

A

Whether cII causes sufficient synthesis of repressor to overcome action of Cro

Genes (6 decks)

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