Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

MB 414 > Bacterial Differentiation > Flashcards

Bacterial Differentiation Flashcards

(62 cards)

Start Studying
1
Q

Types of differentiation

A
  1. Caulobacter
  2. Cyanobacteria (grow in chains)
  3. Myxococcus
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Caulobacter crescentus

A
  • every cell division it undergoes is asymmetric
  • each division results in two types of cells, a motile swarmer cell and a sessile stalked cell.
  • mother cell is always the stalked form of the bacterium.
  • stalk keeps cell docked to the strata of its environment
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

swarmer cells

A
  • the daughter cell
  • will have a flagellum and is motile
  • will swim around by chemotaxing toward nutrients.
  • when it finds a nutrient rich environment, it will lost its flagella and form a holdfast (attachment organ)
  • at the same time as replacing flagellum, the cell will initiate DNA replication
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

cell division in Caulobacter

A
  • only two chromosomes made
  • after the chromosomes have been separated, a flagellum will form on the opposite pole from the holdfast, and cell division can proceed
  • only sessile cells divide.
  • cell division is asymmetric - swarmer cell is smaller than stalk cell in addition to pole structures (holdfast vs. flagella)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Regulation in Caulobacter

A
  • differential expression during caulobacter life cycle
    • flagella are only expressed in swarmer cells
    • chemotaxis proteins only expressed in stalked cells
    • hold-fast only expressed in stalked cells
    • DNA replication only occurs in stalked cells
    • Cell division only occurs in stalked cells.
  • all coordinated by master regulated, CtrA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

CtrA

A
  • regulation of CtrA on 3 levels:
    • transcription
    • phosphorylation
    • proteolysis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Transcriptional regulation of CtrA

A
  • CtrA expressed from two promotors, P1 and P2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

P1

A
  • only transcribed immediately after chromosome division when the DAN is hemimethylated (by ccrM methylase)
  • after DNA become fully methylated, transcription from P1 stops
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

P2

A
  • transcribes CtrA after P1

- controlled by CtrA-P (positive auto regulation)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

ccrM methylase

A
  • recognizes GANTC

- because DNA replication is semi-conservative, new strands ill be hemi-methylated.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

phosphorylation regulation of CtrA

A
  • CtrA must be phosphorylated in order to be active
  • there are multiple kinases that transfer a phosphate to CtrA
  • CckA (Cell Cycle Kinase) is the most important.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Proteolysis regulation of CtrA

A
  • two proteases ClpP and ClpX, which degrade CtrA. Turned on by CtrA-P
  • work in a complex called ClpXP
  • recognize amino acid sequence at C-terminal end of protein called receiver domain (RD)
  • work in conjunction with DivK
  • RD tagged proteins are targets for proteolysis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Targets of CtrA regulation

A
  • regulates generous involved in:
    • cell cycle regulation
    • flagellum biosynthesis
    • DNA methylation
    • chemotaxis
    • holdfast biosynthesis
    • ClpXP proteases
  • represses chromosome replication
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Differential expression in Stalked vs swarmer cells

A
  • due to polar localization of the kinases CckA and DivJ, and well as phosphatase PleC.
  • CckA and PleC localize to the swarmer pole
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

CckA

A

serves to phosphorylate CtrA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

PleC

A

serves to desphophorylate DivD and DivK

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

DivJ

A

localizes to the swarmer pole and is the kinase for DivK and PleD

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

DivK-P

A
  • controls CtrA proteolysis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Differential expression of flagella

A

flagella controlled by phosphorylation status of DivK and PleD

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

PleD-P

A

flagella release

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

When cell division occurs

A
  • DivK and PleD will be active in stalked cell, so CtrA will be degraded by ClpXP (dependent on DivK) and flagella will be repressed
  • Swarmer cells will contain will contain high levels of CtrA, which will continue to activate CtrA dependent genes and repress DNA replication.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

CtrA regulation in swarmer cell. Genes on

A
  • Flagellum
  • CtrA
  • Chemotaxis
  • NO Division
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

CtrA regulation in stalked cell. Genes on

A
  • chromosome rep
  • Clp protease
  • Hold fast
  • Division proteins
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Myxococcus xanthans

A
  • predatory bacteria
  • they eat only protein
  • hunt in packs because when they find prey, they secrete proteases that will degrade the prey and release amino acids.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
gliding motility
- do not swim, they move along the surface by gliding | - social motility and adventurous motility
26
social motility
- the pack will stay together
27
adventurous motility
- sometimes a single bacteria will break from the pack looking for food but will always return to the pack quickly.
28
Starvation conditions
- when they become starved, they will differentiate into a fruiting body and then sporulate - the fruiting body contains about 100,000 cells. - fruiting body makes sure all cells with sporulate together, so that when conditions improve, all the cells can germinate coordinately, since bacteria hunt in a pack.
29
signaling fruiting body formation
- coordinated through 6 signal pathway but most important are A signals and C signals
30
A-signal
- induces aggregation of bacteria
31
C-signal
- induces fruiting body formation
32
Response to starvation
- sense nutrient limitation by using the ribosome to assess the pool of loaded tRNAs - if a ribosome encounters a codon and cognate acyl-aa-tRNA is missing, it will transfer an orthophosphate to the 3' end of GTP to form guanosine tetra-phosphate (ppGpp)
33
ppGpp
- common starvation signal in many bacteria | - required for the A-sinal in M. xanthus
34
A-signal components
- A Signaling Genes (ASG) - AsgA - AsgB - AsgC - AsgD - AsgE
35
AsgA
- membrane kinase
36
AsgB
- DNA bindig protein
37
AsgC
- Sigma factor
38
AsgD
- sensor kinase | - senses extracellular amino acid levels
39
AsgE
- Protease
40
The A-signal itself
- combination of 6 amino acids - Trp - Pro - Phe - Tyr - Leu - Ile - and peptides containing these amino acids.
41
Sensing the A signal
- sensed by two a two component regulatory circuit encoded by sasS and sasR
42
sasS
- senses A-signal | - membrane-bound histidine kinase, which passes the signal to sasS
43
sasR
- response regulator - will activate many genes that use an alternative sigma factor (sigma54). - these genes will start aggregation phase of fruiting body formation, and cells will come together into a large, flat mass. - formation of large 3-D fruiting body requires C-signal
44
C-signal
- once cells have aggregated due to A-signal, the C-signal is turned on - C-signal is the membrane protein CsgA
45
CsgA
- increases response to itself and to cell density (like quorum sensing) - CsgA can never stimulate a receptor on the same cell it is displayed on, and stimulation of a different cell requires close cell contact.
46
C-signal propagation and A-signal crosstalk
- as cell detects more CsgA from other cells, it will produce more of its own CsgA - done through sensing system consisting of actABCDEF - activates master regulator of fruiting body formation, FruA
47
FruA
- master regulator of fruiting body formation - response regulator - it's transcription is regulated by the A-signal and phosphorylation regulated by the C-signal. - controls two pathways, Frz and Dev
48
Frz
involved in chemotaxis and motility
49
Dev
involved in fruiting body development and sporulation
50
Once mature fruiting body is formed
- some cells inside fruiting body will form spores, which will wait for external conditions to improve - germination of spores is done coordinately - internal structure of fruiting body contains spores (coccid cells)
51
Why oxygenic photosynthesis and nitrogen fixation and incompatible?
- The O2 produced by the water splitting enzyme of photosystem II will bind to and irreversibly inactivate the nitrogenase active site.
52
How cyanobacteria get past this
- grow in chains, and one in ten will differentiate into a heterocyst
53
heterocyst
- can fix nitrogen an anaerobic environment, and the fixed nitrogen (in form of amino acids) is shared with neighboring cells through channels between the cells. - the heterocyst will receive fixed carbon in the form of carbohydrate from its neighbors through the same channels.
54
Regulation of heterocyst development
- NctA protein senses nitrogen status in the cell by measuring the level of alpha-ketoglutarate/glutamate ratio.
55
ratio of Alpha-ketoglutarate/glutamate rises
- low fixed N | - NctA will induce N2 fixation along with the het genes that will instruct the cell to form a heterocyst.
56
problem of cyanobacteria
- only wants a maximum of 10% of its cells to become heterocyst
57
How cyanobacteria count to 10
- when sensing low N PatS is turned on by NctA
58
PatS
- an inhibitor of differentiation | - the first cell to make significant amounts of PatS will be the one that will form the heterocyst.
59
How PatS works
- most likely binds to and inhibits an important regulatory protein that acts early in heterocyst formation - PatS is made and exported by the first cells to sense N-starvation. - It diffuses into and through adjacent cells, and a concentration gradient of the protein is set up, cells nearest the heterocyst get the highest dose and it decreases as the cells get further away. - About 10 cells away, the level of PatS is low enough that the cell can initiate heterocyst formation.
60
once the cell has differentiated to the point of making PetS
- it is immune to the inhibition.
61
Expression of Nif through recombination
- in vegetative cells, two nitrogenase operons are interrupted by an 11 kb DNA segment bound by 11 bp - nonreversible regulation
62
XisA and XisF recombinases
- stimulated by NctA | - removes the insertion sequences and make a functional Nif operon.

MB 414 (26 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions