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Gene to Function - prokaryotes > Lecture 10 - Cell division in bacteria and archaea > Flashcards

Lecture 10 - Cell division in bacteria and archaea Flashcards

1
Q

What is the cell cycle in a prokaryotic cell?

A

Growth, replication and segregation are connected

  • a unit cell has a circular chromosome, phase of cell growth
  • replication initiates when cell passes a critical size
  • replication generates catenated daughter chromosomes
  • daughter chromosomes are separated
  • septum forms at midcell and divides cell
  • daughter cells separate
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2
Q

What is binary fission?

A

The cell splits into two equal-sized daughter cells, each conaining a copy of the mothers genetic material

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3
Q

What is the process of formation of the division septum?

A
  • cell begins with an annulus at midcell
  • new annuli are generated
  • new annuli move in a polar direction
  • new annuli stop movement at1/4 and 3/4
  • central annulus matures into a septum
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4
Q

What is the annulus?

A

the annulus is a ring around the cell where the structure of the envelope is altered

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5
Q

What does the septum consist of?

A
  • the same components as the cell envelope
  • inner membrane
  • peptidoglycan
  • outer membrane
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6
Q

How do mutations affecting cell division also affect cell shape?

A

fts mutants give long filaments
-because the septum fails to form to divide the daughter bacteria
fts=filamentous temperature sensitive

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7
Q

What is the function of the cell division protein FtsZ?

A

-assembles into a ring at the future site of cell division
-1st assembly protein to localise at the cell division site then recruits other proteins
-FtsZ is an anestor of tubulin
can be visualised via fluoresence microscopy bia GFP fusion

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8
Q

What evidence is there that the cell divsion protein FtsZ is an ancestor of tubulin?

A 
tubulin forms microtubules 
-involved in mitosis (chromosome segregation)
-in eukaryotic cell
FtsZ forms a cell division ring
-in bacterial

Structures are v similar
Both for division of genetic material

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9
Q

What are the features of FtsZ?

A
  • highly conserved protein that is found in most bacteria an in the euryarcheal branch of archaea
  • found in chloroplast, involved in chloroplast division
  • present in all three domains of life
  • structural homolog of tubulin
  • GTPase
  • GTP binding induced FtsZ self-assembly into protofilaments
  • forms the Z ring at midcell
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10
Q

What is the order of formation of the Z (cell division) ring?

A
  1. FtsZ arrives at midcell, and acts as a scaffold for other cell divison proteinsW
  2. FtsA, ZipA and ZapA are recruited to midcell
    - FtsA and ZipA anchor Ftsz ring to the inner membrane of the cell
    - ZapA can crosslink FtsZ binding protein individual polymers
  3. FtsE and FtsX arrive next
    - role unknown
    - have homology to the ABC transporter cell (membrane proteins responsible for the transport of solutes inside/outside the cell
  4. FtsK, a long thin membrane protein is next recruited
    - coordinates cell division with chromosome segregation
  5. FtsQ, L and B form a trimer and act as a ‘nucleator’ to recruit other proteins
  6. FtsW and I arrive and begin to synthesise the peptidoglycan cell wall through the crosslinking of different layers of murein through transpeptidase reaction
  7. FtsN (role unclear) arrives
  8. AmiC arrives and with EnvC results in peptidoglycan hydrolysis (cell separation) as they are enzymes (hydrolases)
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11
Q

What are the two stages of the assembly of the cell division ring?

A

Early assembly step
-zap, zip, FtsA, FtsZ
Late assembly step
-FtsX,E, K, Q, L and B, W, I, N, Amic and EnvC

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12
Q

What is involved in cell division in archaea?

A

FtsZ present in euryarchaea not in crenarchaea, different proteins mediate cell division

  • cdvA (archaea specific factor)
  • cdvB and cdvC (homolgous to eukaryotic ESCRT)
  • splits by binary fission
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13
Q

What are ESCRT proteins?

A

Endosomal sorting complex required for transport

-invovled in the formation of membrane vesicles involved in protein and viral trafficking in the cell

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14
Q

How does the cell division machinery find the midpoint?

A

-spatial control of cell divsion-site placement
through:
1. The minCDE site-selection system
2. Nucleoid occlusion (NO)

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15
Q

What is the MinCDE system summary?

A
  1. three proteins that are necessary for cell division site placement
  2. MinC interacts with FtsZ an inhibits its polymerisation
  3. MinD recruits MinC and MinE to the membrane, and forms a complex with MinC
  4. MinE limits MinC activity to the poles
  5. MinCD oscillates from pole to pole in the cell
  6. MinCD moves along a helical structure that extends along the entire length of the cell (visualised nby immunofluorescence microscopy studies)
    - in the absense of the MinCDE system, cell division occure at the poles and this generates minicells
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16
Q

Who worked out the MinCDE system?

A
  • Rothfield
  • Piet de Boer
  • Lutkenhaus
  • Errington
17
Q

What is nucleoid occlusion system?

A

Noc - in bascillus subtilis
SlmA - in Escherichia coli

  • perform the same function but do not share sequence similarity
  • both Noc and SlmA are DNA-binding proteins that assocaite with the nucleoid
  • creates a zone of Min division inhibition
  • when the nucloid is duplicated and moves to either side of a long cell, the gap is where cell division septum is formed
18
Q

What is SlmA?

A
  • an antagonist of FtsZ polymerisation

- maps specifically to 20 different sites all over the chromosome, not just at the terminus

19
Q

What experimental assay can be used to identify whether proteins have bound to DNA? (e.g. SlmA to DNA)

A

Band shift

  • fragments of DNA are incubated with protein and run on a gel
  • if the protein binds, the DNA forms a band that is shiftde compared ti the unbound DNA as it is biggger
20
Q

What is the process of daughter cell separation?

A
  1. constriction of the FtsZ ring pulls the cytoplasmic membrane inward
  2. when the membrane invaginates peptidoglycan synthesis follows (due to the action of FtsI and FtsW)
  3. whilst the peptidoglycan is synthesised, various hydrolases work together to split the peptido glycan to separate daughter cells
21
Q

What molecules are involved in the MinCDE system and what are they?

A

MinC: cell division inhibitor
-interacts with FtsZ and prevents the formation of a stable FtsZ ring (inhibiting FtsZ polymerisation)
MinE: topological specificity factor that gives site specificity to MinC, limiting its activity to the poles
MinD: membrane protein, responsible for the membrane association of MinC and MinE. ATPase

22
Q

What occurs in cells with MinCDE mutants?

A

-polar division resulting in minicell without chromosome

23
Q

What is the function of the MinC and MinD complex and what is it dependent upon?

A

MinC and MinD proteins form a complex that oscillates from pole to pole every ~30seconds
-oscillation is MinE dependent

24
Q

What is the process of MinC/D oscillation?

A
  1. MinD and MinC are associated with the membrane at the poles and recruit MinE
  2. when MinD has saturated one pole of the cell it begins to spread to the middle of the cell
  3. MinE then polymerases into a ring and sweeps away MinC and MinD from the central part of the cell
  4. MinD migrates to the opposite poles and begins again

Never present at midcell, confined to the polar region

25
Q

What is the mechanism of polar zone assembly and disassembly?

A
  • minD recruits MinC to the poles
  • minE stimulates the ATPase activity of MinD
  • hydrolyses to ADP so that MinD can no longer bind to the membrane and so it dissociates
  • can now convert ADP to ATP and start the cycle at the opp pole of the cell
26
Q

In what way does the MinD MinC complex movce?

A

-along a helical track along the periphery of the cell, underneath the cell membrane

27
Q

What is the transpeptidation reaction in the peptidoglycan?

A
  • catalysed by FtsI
  • made up of NAM and NAG
    1. The free amino group (NH2) on the third amino acid (L-lysine) of a NAM side chain forms a covelent link with a D-alanine on an adjacent murein strand
  • the free D alanine is now taken back into the cell to be resued

Gene to Function - prokaryotes (12 decks)

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