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Summary progress exam 3 - Bacteriology
Summary of all the lectures for progress exam 3
[Meer zien]Voorbeeld 4 van de 33 pagina's
Voorbeeld 4 van de 33 pagina's
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Voorbeeld van de inhoud
5 novemberAdvanced Bacterial Physiology 1 & 2
Video 1:
Morphology is cell shape → there are different shapes
Morphology does not predict physiology, ecology, phylogeny of a prokaryotic cell
- Selective forces are involved in setting the morphology
- optimization for nutrient uptake (e.g. star shape)
- swimming motility in viscous environment
or near surfaces (e.g. flagella)
- gliding motility
E.coli (gram negative bacteria) as example → 60%
Duplication of the genome:
Bacteria: double stranded circular DNA, even short
structures encode for RNA
- DNA not in a nucleus
Bacteria have 1 origin of replication per chromosome
- 2 replication forks going in opposite direction →
lagging & leading strand = semiconservative
DNA replication → till 2 replication forks beat
each other at the terminator → 2 new circular
DNA (1 old and 1 new) → segregation in
daughter cell
- DNA helicase: separates the double stranded
DNA
- DNA polymerase has access to make a
new copy
- Synthesis: 5’ to 3’
- Lagging : short fragments: Okazaki fragments :
initiated by a primase
- Single stranded DNA : bounded by single
stranded binding proteins → no degradation
- Lagging strand → looped around
- DNA ligase: all the lagging strand sticking to each other → continuous strand
Eukaryotes: multiple origins of replication
Video 2:
Bacteria can grow very fast (every 20 min)
- replication : takes 40 minutes
- segregation: 20 minutes
- cell cycle: 20 minutes
How do bacteria but 60 minutes into 20 minutes? → Multiple fork replication
,Multiple fork replication:
They have to initiate replication already when the cell is not segregated
→ Dividing cells are bigger (nutrient rich medium)
Thus: The genomes present in a fast growing bacteria are different, because they are in
different stages of the replication cycle, resulting in different number of genes copies, but the
genes are the same
Video 3
Gram positive: stained by gram staining → thick peptidoglycan layer
- peptidoglycan: lipoteichoic acid and teichoic acid
Gram negative bacteria: 2 membranes (outer & plasma) & thin peptidoglycan layer
- periplasm (no ATP)
- lipopolysaccharides on the outside : long sugars connected to fatty acids
(hydrophilic) & membrane is hydrophobic: difficult for molecules to get through this
layer
- outer membrane pores: allow access of small molecules
- <600 dalton (medicin <600 D) to get acces to gram negative bacterium
- makes it harder to target gram negative bacteria
Peptidoglycan layer determines shape:
Peptidoglycan layer can survive boiled water (heat) → protects bacteria against turgor
pressure from inside
- Peptidoglycan keeps the content of the bacteria inside
- Peptidoglycan has D-ala-D-ala, normally we have L amino acids, but peptidoglycan
had D-amino acids
- Peptidoglycan consist of sugar strands
- disaccharide peptides → cross linked by transglycosylation
- peptide cross links are made by transpeptidation (by penicillin binding
proteins)
- Peptidoglycan is synthesized by Penicillin Binding Proteins (PBP)
- last amino acid is removed → provide energy for crosslink, because there is
no energy in the periplasm
- different classes PBPs (A-C)
- transpeptidase is inhibited by beta lactams such as penicillin/ampicillin
Thus: Transpeptidases need the energy of the removal of the last amino acid, because in
the periplasm we do not have energy providers such as ATP or NADP
Peptidoglycan
- Peptidoglycan is synthesized in the cytoplasm → add different amino acid → added
to bactoprenol → flip across membrane by MurJ → crosslinking by
, transpeptidases→ connect side chains while removing the last amino acid
(D-alanine)
- Lipid 2 = precursor Peptidoglycan
Penicillin Binding Proteins (PBPs)
- Transpeptidases
- Donor and acceptor site
- Penicillin is similar to D-ala-D-ala
- when PBP bind penicillin → can not get rid of penicillin anymore (covalent) →
penicillin in donor site → no cross linking anymore
- Penicillin kill only growing bacteria, so non growing bacteria are resistant to
antibiotics (dormant)
2 modes of Peptidoglycan (PG) synthesis:
1. Elongation of length growth: randomly new material is inserted in the cell
2. Cell Division: complete new synthesis of the new cell poles
Length growth:
Most rod bacteria (staafjes) have MreB (actin homolog) : elangasome
- no MreB: cells become a circle and they cannot grow in length
MreB recruits protein in length growth (RodA & PBP2) : insert new PG → must MreB forward
→ insertion of new material in the cell wall
Cell division:
Inhibit cell division → bacteria become filamentous (lang filament)
For cell division we need a Z-ring
Ftsz: tubulin homolog, but ftsz forms never a microtubule
- FtsZ is bound to GDP → replaced by GTP → FtsZ starts to polymerize → hydrolysis
of GTP to GDP → continuous polymerization and depolymerization (treadmilling)
- Ftsz is a ring
How does the cell know where the middle is?
Ftsz: form a ring in the middle
SlmA (Noc): inhibits polymerisation of Ftsz = Nucleoid occlusion
- SlmA (Noc named in E.coli)
You can still polymerize close to the pole → minicell : no DNA → not viable: waste of energy
- prevent forming Ftsz at the cell pole → Min system (CD)
- MinD: bound to membrane
- MinE: activated Atpase activity of minD ATP hydrolysis → ADP
- MinC: inhibits Ftsz polymerization
- Min CD bound to membrane → oscillation movement around the poles every 20
seconds → this causes the poles to be insensitive for Ftsz
- Min system costs a lot of energy → but it prevent mini cells
So, the absence of min system and local minimum NOC allows FtsZ polymerization at the
middle of the cell → cell division
Video 4:
The difference between eukaryotes and prokaryotes:
FtsZ recruits divisome → synthesizes new cell poles for division
Ftsz is always at the leading edge of the constriction
, - FtsW with PBP3 : insert material into the cell wall
Can we add a time scale to the assembly of this whole complex?
The growth cycle:
lag phase: they have to adapt to the new
environment
exponential phase: fast replication
(determine age of the cells)
- grow → dilute → grow → dilute :
metabolism is adapted to
environment → bacteria grow as
fast as the medium, thus average
mass = average bacteria number:
constant age frequency distribution
stationary: resting stage
→ Immunolabeling: you can investigate wild type cells → E.coli → permeabilize → add
fluorescently labeled antibodies → fluorescent ring structure
- large cells has Ftsz
- first protoring with Ftsz → second PG synthesis
Ftsz is tread milling & PG synthetic complex is following:
Ftsz grows on 1 side and loses monomer on the other side → PG synthesis moves at the
same speed with FtsZ: amount of FtsZ determines the closure
Video 5:
Main focus on E.coli, but not so wise to focus everything on
1 bacteria species, because E.coli is not so standard.
- E.g. nematode is covered with bacteria : they are
rod shaped and bind with 1 pole to the bacteria →
they grow longitudinal (E.coli perpendicular) →
daughter cell would be lost therefore these bacteria
grow longitudinal
- they have a FtsZ → is not a ring anymore,
but an ellipse in these bacteria → there are
different types of FtsZ!
Important knowledge:
Prokaryotes do not have internal organelles. DNA is freely present in the cytosol termed
nucleoid in contrast to nucleus in eukaryotes. An organelle in a eukaryotic cell is surrounded
by its own membrane and is also duplicated in each cell.
A bacterial genome is circular and both DNA strand encode genes.
→ Its duplication occurs bidirectionally.
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