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Hilary Term 1 > Prokaryotic Genomes and Cell Division > Flashcards

Prokaryotic Genomes and Cell Division Flashcards

1
Q

Describe the genome of Escherichia coli

A
  • 4.6Mb of circular DNA
  • 300 plasmids
  • measured using 100minutes time mapping of Hfr mating
  • approximately 40 minutes to replicate and divide
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2
Q

Describe chromosomal replication

A
  • begins at the origin
  • is bidirectional (there is a replication fork in both directions)
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3
Q

Describe the G1 phase of chromosomal replication

A
  • DnaA-ATP binds to fully methylated oriC for initiation
  • once oriC reaches critical concentration, it fires all the oriCs in the cell at one: it is an all-or-nothing response
  • results in DNA replication and hemimethylation to form DMNA, allowing the S phase
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4
Q

DnaA exists at

A

low levels in the cell

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5
Q

Describe the S phase of chromosomal replication

A
  • SeqA blocks the oriC regions, displacing DnaA and resulting in cell elongation by forming a ring at the centre of the cell
  • DnaA must reach a critical concentration as the cell grows
  • HdaA hydrolyses DnaA-ATP to Dna-ADP
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6
Q

Describe SeqA

A

homologous to tubulin

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7
Q

Describe the G2 phase of chromosomal replication

A
  • results in chromosomal segregation and partitioning, and separation of the two nucleoids
  • ParB is located at the old pole, and is bound by PopZ, whilst simultaneously binding to the DNA at the parS sequence
  • drawn towards the new pole by the activity of ParA
  • Z-ring forms, and the cell divides
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8
Q

Describe visualisation of the G2 phase of chromosomal replication

A
  • usually modelled using the stalked cells of Caulobacter (since the Par genes are absent in E. Coli)
  • most effectively visualised using fluorescent tags
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9
Q

Describe variation in replication fork usage

A
  • in bacteria with a very fast generation time, up to 5 replication forks form on oriC
  • others, such as E. Coli, use only one.
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10
Q

Where are very large plasmids found?

A

Rhizobia

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11
Q

Describe the shape of plasmids

A
  • usually linear
  • can be circular
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12
Q

Which genes do plasmids contain?

A
  • not necessary for survival, but for accessory functions
  • pathogenesis
  • metabolism
  • symbiogenesis
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13
Q

Describe R plasmids

A
  • resistance plasmids
  • confer antibiotic resistance
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14
Q

Describe bacteriocins

A
  • found on plasmids
  • kill related bacteria
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15
Q

Describe tra genes

A

make them mosibilisable and self-transmissible via the production of a conjugation bridge

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16
Q

Describe incompatibility groups

A
  • a way of organising plasmids
  • two plasmids from the same incompatibility group are very similar, and interfere with each other’s replication
17
Q

Describe plasmid replication

A

plasmids are autonomous and replicate independently of the genome, sometimes poles away from the nucleoid

18
Q

Give an example where a plasmid replicates poles away from the nuclei

A

large ColE1 plasmids

19
Q

Describe bacterial cell division

A
  • requires the divisome complex
  • FtsZ assembles at the cell equator in a ring structure
  • attached to the cell membrane by ZipA while converting GTP to GDP and Pi
  • FtsA recruits FtsZ to transform ATP into ADP and Pi
  • FtsZ polymerisation is prevented by MinCD, which oscillates in concentration mostly between poles as a ring
  • oscillation induced by MinE, which disperses it at one pole, inducing reassembly at the other
  • MinCD levels are lowest at the cell equator: this is where FdsZ polymerisation will occur.
20
Q

Describe the divisome complex

A

comprised of FtsZ, FtsA, ZipA and other proteins

21
Q

Describe FtsZ

A

tubulin-like

22
Q

Describe FtsA

A

actin-like

23
Q

Describe FtsI

A
  • penicillin binding protein
  • necessary for peptidoglycan synthesis
24
Q

How is the rod shape in rod-shaped bacteria formed?

A

MreB forms in bands and spirals perpendicular to the cell wall, connecting to the cell membrane and directing peptidoglycan synthesis

25
Q

How do concave bacteria such as Caulobacter crescentis create their shape?

A

contain proteins such as crescentin that localise at the curved surface to induce a concave structure, perpendicular to the cell wall

26
Q

Describe dispersed cell wall synthesis

A
  • lateral
  • occurs at multiple points on the cell wall
  • bands of peptidyglycan are dispersed along lines of the cell wall
  • dependent upon the activity of MreB for connectivity.
  • E. Coli and Bacillus
27
Q

Which organisms use budding?

A

some alpha-proteobacteria such as
- Hirschia baltica
- Anacalomicrobium adentum
- Prosthecomicrobium hirschii
- Rhodoseudomonas plaustris
- Rhodomicrobrium vannielii
- Hyphonmicrobium denitrificans
- Sagittuis stellata

28
Q

Describe cell wall synthesis in polar organisms

A
  • polar bacteria do not hae MreB
  • new cell wall is made at the pole(s).
  • Agrobacterium tumefaciens
  • Brucella suis
29
Q

Describe cell wall synthesis in Gram positive Cocci

A
  • lack MreB
  • grow a band from the middle
  • FtsZ ring grows in a growth zone between wall bands, creating a central deposition of new cell membrane and wall
  • forms a septum and a septated cell.
  • Streptococcus
30
Q

Describe peptidoglycan dipeptide biosynthesis

A
  • linking of the peptidoglycan precursor NAG-NAM-pentapeptide to the C55 alcohol bactoprenol in the cytoplasm
  • hydrophobic bactoprenol carrier is then loaded, and can then carry the peptidoglycan unit across the cytoplasmic membranes lipid bilayer, to the peptidoglycan layer
  • autolysins hydrolyse the glycosidic bonds in its backbone
  • transglycosylases stitch in a new unit
  • once D-Ala is released, transpeptidases crosslink DAP to D-Ala to form transpeptide cross-links, flipping the dipeptide into the chain
31
Q

What is the peptidoglycan layer?

A

The growing point of the cell wall

32
Q

Describe the action of penicillins

A

inhibit transpeptidation

33
Q

Which antibiotics target the cell wall?

A
  • Vancomycin (via DL/DR, causing cell breakdown)
  • Bacitracin
34
Q

Which antibiotics target the cytoplasmic membrane?

A

Daptomycin

35
Q

Which antibiotics target the chromosome?

A

Quinolones

36
Q

Which antibiotics target RNA polymerase?

A
  • Rifampin
  • Actinomycin
37
Q

Which antibiotics target the 70s ribosomal subunit

A
  • Puromycin (which terminates peptide synthesis)
  • Streptomycin
38
Q

List some resistance mechanisms

A
  • beta-lactamase
  • modified porins
  • an alternative PBP
  • an efflux pump
39
Q

Describe vancomycin resistance

A
  • vancyomycin binds in peptidoglycan synthesis to DL and DR, breaking down the membrane
  • VanR has evolved to detect problems in the cell membrane, phosphorylating VanS and beginning rescue biochemistry

Hilary Term 1 (61 decks)

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