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Neur2001 > Bacteriophage Lambda > Flashcards

Bacteriophage Lambda Flashcards

1
Q

What are the 3 phage classifications:

A
  1. Filamentous phage (simple) - a piece of nucleic acid wrapped in protein sub-units -> less limitation
  2. Isocahedral head with/without tail
  3. Nucleic acid can be single-stranded, double-stranded/ linear
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2
Q

In which state is replication reduced in a bacteriophage?

A

Lysogeny

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3
Q

What is the difference between a bacteriophage which is virulent and one that is temperate?

A

Virulent - only lytic growth

Temperate- have choice of either

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4
Q

Prophage

A

Phage DNA in lysogen

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5
Q

Immunity

A

Bacteria can’t be infected by other phages because single integrated prophage protected by repressor -> replication can’t occur since PL and PR switched off

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6
Q

Induction

A

Prophage is freed from lysogeny by excision

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7
Q

Lysogeny favours

A
  • low levels of nutrients
  • high multiplicity of infection (more virus than bacteria)
  • > if clear plaque more virus
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8
Q

Bacterial growth occurs

A

once lysogeny is established

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9
Q

Early infection

A

Entry of DNA to replication

  • relies on transcription apparatus of host cell -> only a few genes expressed and promotors are same as host
  • accumulate phage genome
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10
Q

Late infection

A

replication to release of prophage

  • synthesis of protein components -> head/ tail
  • assembly proteins
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11
Q

When structural components assemble into heads/ tail

A

Host cells lysed to release new viral particles

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12
Q

Lytic cycle is under ____ control

A

positive

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13
Q

Expression starts when ____ protein is coded by ____ genes

A

Regulator, early

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14
Q

Does the bacteriophage continue to express the initial set of genes?

A

Depends on control circuit:
1. If transcription initiation: early genes can be switched off when middle genes transcribed since ind. transcription units + mRNA
2. If transcription termination:
early genes continued to be expressed since transcription units must be adjacent for control at termination. -> single mRNA for both sets of genes + phage functions mainly controlled by 2 sets of early genes.

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15
Q

Late genes

A

Expressed when phage DNA replicated -> embed additional regulator gene in previous set of genes e.g. anti-termination factor

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16
Q

A sigma event

A

redirects specificity of host RNA polymerase

17
Q

An antitermination event

A

Allows host RNA polymerase to read through termination sites between adjacent early genes + join adjacent sequences ( early gene seq. 3’ + new at 5’)

18
Q

Example of an antitermination event in lambda

A

pN (coded by gene N) allows RNAp to read through terminators located at ends of immediate early genes -> pQ later acts with pN to transcribe late genes

19
Q

How are phage promoters recognised?

A

Switching. Sigma factor from host is replaced with another factor that redirects its specificity in initiation so a new phage RNAp is synthesised which has different host promoters than host RNAp.

20
Q

Lambda Characteristics

A

Isocahedral head (DNA linear) with tail but is circular in bacteria.

  • double- stranded
  • 12bp cos ends
  • 46 genes, 48,514 bp
  • cascade system so not all genes expressed at same time -> works b/c circular
21
Q

Lambda has 2 immediate early genes:

A

N and cro - transcribed by host RNAp

22
Q

Delayed early genes:

A

3 of products are regulators including cii and ciii

23
Q

Lytic cycle requires which genes?

A

early gene cro and delayed early gene Q

24
Q

Late genes form a

A

single transcription unit

25
Q

Lambda repressor protein is coded by

A

cI -> transcribed from PRE

26
Q

Why are cii and ciii regulatory?

A

ci is not immediately recognised by RNAp so cii needed for conformational change so RNAp can recognise weak promotor + cause anti-sense transcription of cro (repressor lysogeny)
ciii binds to cii which prevents degradation by HFL-A proteases present in bacterial cells

27
Q

Functions of lambda repressor

A

Acts at OL and OR to block transcription of immediate early genes -> turns off PL and PR + turns on PRM
-> immediate early genes trigger a regulatory cascade which prevents lytic cycle

28
Q

PI turns on….

A

additional expression of integrase to integrate lambda to bacterial DNA

29
Q

anti-PQ

A

anti-sense hybridisation to decrease expression of Q transcript -> decrease lysis

30
Q

How does integration occur ?

A

Lambda and bacteria integrate with complimentary attachment sites: attP + attB (POP + BOB) where O is the same sequence

  • > intersome for site-specific recombination is coded by integrase + IHF
  • > once integrated -> lambda POB + BOP joined
31
Q

Excision uses

A

xis ( recognises att sites) and integrase

Neur2001 (10 decks)

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