10. Bacterial cell division and differentiation (endospores) Flashcards
What’s divisome made out pf
Proteins that allow cell division
What’s step by step bacterial cell cycle
- Initiation of DNA replication
- Bi-directional replication
- ParA/ParB-mediated bi-polar attachement
4.Decatenation - Septation
- Origin detachement
- Cell division
Summerize what happens during bacterial cell cycle
As cell readies for genome application, oriC migrates to the poles of the cell and the replisome assembles. Cell elongates as chromosome replication and partitioning continues. Chromosome seperate as septation continues. Daughter cells divide
What processes in bacterial cell cycle happen concurrently
Chromosome replication and partitioning and overlap septation
Where is replication machinery located
Where cell division occurs
Where are Ori and Ter initially and where are they after
Initially, at midcell and then at the opposite parts of the cell
what proteins are involved in the formation of the septum
FtsZ
Fts(Filamentous thermosensitive proteins)
What are steps of septum formation
- Selection of the site
- Assembly of the Z ring, composed by FtsZ
- Assembly of the cell wall-synthesizing machinery
- Construction of the cell and septum formation
What’s FtsZ
FtsZ- GTP-binding protein that introduces a curve into the structure after hydrolysis of GTP and forms a ring at the site where the division septum will form. It’s essential and found also in mitochondria and chloroplasts
What allows septum formation
Treadmilling process of FtsZ
What is another role of FtsZ except formation of Z ring
Recruiting other proteins at the site of formation of the septum
What is the role of other Fts proteins
-support the formation of the Z-ring and stabilize it
-recruit and stabilize replisome at division site
-unlock replicated DNA from the division site and separate it into the two daughter cells
-direct the membrane and cell wall imagination
What proteins determine site for the formation of the septum for the cell division
Min(Minicell):
minCD and minE
What happens when minCD mutates
In mutants of minCD operon, the septum is formed in an asymmetric position. The resultant minicells are achromosomal
What does minCD do in wild type cells
MinCD protein localizes at the cell poles and inhibits the septum formation at these sites. Z-ring formation can occur only at midcell
How does MinCD moves
It moves from one pole to the other. Oscillation takes about 10sec and this time allows the formation of a gradient of MinCD with minimal concentration in the middle of the cell
What assists MinCD movement
MinE. It forms a ring the displaces MinCD from the central part
What is the result of combined action of MinCD and minE
Determination of formation of septum only in the central position
What is MinD
MinD-transmembrane protein and has ATPase activity
What is needed for MinC activation
ATP hydrolysis
What does MinCD-ATP complex do
It determines the inhibition of the formation of the ring by FtsZ
When does FtsZ ring occur
Only after the daughter chromosomes have separated
In what positions does MinCD inhibit septum formation
1/4 and 3/4
What does MinE favor
Formation of the Z-ring at midcell and it has inhibitory effect on MinCD
How is septum formed
By cell growth with synthesis of new cytoplasmic membrane and wall
What are mesosomes
membrane invaginations(being turned inside out) as anchor points for the chromosome
What is the function of mesosome
-Assistance during the replication of nucleoid material
-Involvement in the formation of the septum during the cell division into 2 daughter cells
What determines movement of origin of replication towards opposite cell poles
FtsZ, MreB and crescentin
What is cytoskeleton made out of in eukaryotic cell
Microfilaments, Microtubules, Intermediate filaments
What are MreB, FtsZ and crescentin functional homologs of
MreB of actin, FtsZ of tubulin and crescentin has structural domain similar to intermediate filaments
Where can FtsZ, MreB and crescentin be found
FtsZ in all bacteria, MreB in non-spherical bacteria and crescentin in bacteria with curved homology
What happens in E.Coli if there is no production of MreB or FtsZ
No MreB- loses cell morphology and become spherical
No FtsZ- do not form division septum and acquire rod-shaped morphology
What happens to Caulobacter mutants that don’t produce crescentin
They acquire normal rod-shaped morphology, Asymmetric cell wall gives rise to the inner curvature
What happens in division of spherical shaped bacteria
New synthesis is localized at the single site. When cells divide, they have one old and one new hemisphere, seperated by crests
Where does synthesis of cell wall at Gram + bacteria happen
At the Z-ring
Where is cell wall synthesized at rod-shaped cells
MreB wraps around rod-shaped cell like a spring connecting different sites of the cell membrane. These sites are the same sites where cell wall is synthesized, not at the poles.
Where does DNA replication happen in bacteria and where in eukaryotes
bacteria: through entire cell; eukaryotes: only a part
What happens when we stop DNA synthesis
We stop cell division
How do we ensure that each daughter cell receives the same portion of genetic material
By coordinating replication and division
When are more than 1 replication forks present during chromosome replication
When cell has a doubling time<60 minutes
What is specific about bacteria with slow growth rate
There is only one points of replication of the chromosome. The replication takes only a portion of the cell cycle and there are intervals during the synthesis of DNA
What’s differentiation in prokaryotes and eukaryotes
Eukaryotes: specialization processes pf the cells
Prokaryotes: strucutural changes that can be observed in the single cell
What are some structural changes in bacterial cell
-formation of the divisome
-differentiation and de-differentiation of appendices
-activation of chemotactic system and motility
-acquisition of competence( to transformation)
-sporulation process
What are mechanisms that regulate differentiation
- cell polarity
- distribution of regulatory proteins in particular cell compartments
What is specific about sporulation of Bacillus subtilis
During sporulation, cell forms endospore at one pole of the mother cell , while the other half of the cell is destined to death
What important about differentiation of Caulobacter crescentus
cell division generates two different types of specialized bacteria. Each of them develops, alternatively, specialized organelles
Can cell poles be different from each other
Yes and they can also have different properties compared to other regions in the cell
What are endospores
Under particular environmental conditions (conditions that can ensure only suboptimal nutrition factors concentrations) sporigenic bacteria undergo progressive morphologic and structural changes that lead to the generation of the spores.
What bacteria are sporogenic
Only few Gram + bacteria: Clostridium, Steptomyces, Bacillus
What are some diseases that spores can cause
Tetanus, botulism, gas gangrene
What does sporulation lead to
Sporulation(sporogenesis) within vegetative cell leads to the generation of endospore, which is characterized by different properties in terms of both composition and function
When does sporulation start
In late exponential/early stationary phase and requires 6-8 hours
How do we stain endospores
With malachite green and after washing with water counterstaining with safranin(endospores are green)
Where can endospores be located
-central spore
-subterminal spore
-terminal spore
- terminal spore but when diameter of the spore is higher than that of the mother cell
What does endospore contain
Complete copy of the chromosome, minimal concentrations of essential proteins and ribosomes, high concentration of calcium complexed to dipicolinic acid, which is essential for thermic resistance by acting on stabilization of the sporal proteins
What is the the structure of endospore
1)Core
2)Cortex
3)Coat
4)Exosporium
What is the core of endospore
Core- DNA, ribosomes and enzymes, calcium dipocolinate. There in no mRNA. DNA is complexed to proteins with low molecular weight proteins(SASP=small acid soluble proteins) that make it resistant to UV light. All is then enclosed by the inner membrane and wall residues(germ wall)
What is cortex of endospore
Cortex- double layer of peptidoglycan, calcium dipicolinate and diaminopimelic acid
What is the coat of endospore
Coat- Sulfur-containing proteins, rich in cross-linking that transfer resistance and chemical agents(keratin-like proteins)
What is exosporium of endospore
It’s not always present. It contains proteins-lipids-polysaccharides (phospholipids,teichoic acids,diaminopimelic acid)
Why are spores resistant to heat, chemical and physical agents
-Extreme dehydration of the protoplast, absence of protein synthesis and presence of cortex(electronegative and hydrophilic peptidoglycan polymer)
-Mineralization of the protoplast (Ca2+,Mg2+,Mn2+,K+)
-Presence of calcium dipicolinate-replaces water and stabilizes DNA
-Presence of the coats and cortex-potent barriers to the intake of substances and chemical agents
-Presence of SASP proteins in the cytoplasm that interact with DNA and protect it from UV-induces damages
What do sigma factors do in sporulation
Sigma F/holoenzyme: activates early sporulation genes, activates the transcription of sigma G, that upon activation activates sporulation genes
Are activation and germination reversible or not
Activation is, germination isn’t
Explain process of sporulation
Upon sensing certain environmental conditions, endospore forms activate Spo0A and initiate sporulation. First morphological event is the formation of polar septum which creates larger mother cell and smaller forespore. Mother cell engulfs forespore, and the two cell work together to assemble the dormant spore. Calcium dipicolinic acid(Ca-DPA) is synthesized in the mother cell and transported into the forespore in exchange for water. The cortex is formed between the two membranes, and coat proteins polymerize on the surface of the mother cell-derived membrane. Once the spore is mature, the mother cell lyses and releases the dormant spore in the enviroment
Explain germination
Upon sensing appropriate environment small molecule germinates, the spore initiates a signaling cascade that leads to activation of cortex hydrolases and core hydration which is necessary for metabolism to resume in the germinating spore
