17 Bacterial Cell Structure Flashcards
what do macrophage attracting neutrophils (monocytes) secrete
IL-1-beta
TNF-alpha
IL6
what are bacteria
simple prokaryotic structure
where is the DNA in bacteria
DNA free in cytoplasm
what do some bacteria have that the immune system recognise
some bacteria have extra layers outside cell wall (recognised by immune system and not eukaryote-like)
what are prokaryotes the size of
size of a mitochondrion in eukaryote
where can pathogenic bacteria live/replicate
pathogenic bacteria can live/replicate inside eukaryotes
what are bacteria often named for
characteristic shapes due to their cell wall and cytoskeleton structures
sphere bacteria example
streptococci
rod bacteria example
Bacillus anthracis
spiral bacteria example
Aquaspirillum
spirochetes bacteria example
borrelia
what is borrelia like
very thin, flexible wavy shaped spirochetes, immune evasion and cause disease
no cell wall bacteria example
mycoplasma
what is mycoplasma like
no wall so can live inside human cells and the body without giving cell wall signals
what is cell shape associated with
walls which give strength and robustness to bursting
why is bacterial surface structures important
Major surface contact points between bacteria and the immune system
Important functional structures in commensal and pathogenic bacteria
why do bacterial surface structures change
vary structures to evade immune recognition
how do we examine bacteria
Simple microscopic staining of bacteria and examination with a light microscope reveals their morphology (µm scale)
how do we examine bacteria to high resolution
high resolution of surface structures like flagella (nm scale) you need electron microscopy and negative staining with electron dense materials
why does DNA leak from bacteria
DNA in cytoplasmic membrane of prokaryotes (easily leaks out if cell burst), wall prevents bursting, many Gram-negative bacteria have an extra outer membrane and structures beyond the wall
what is bacterium structures encoded from
Every structure of the bacterium is encoded from its DNA
how does bacteria and human DNA differ
DNA of bacteria has different codon usages to humans and is differently modified (acetylated/methylated)
what is bacteria like in humans an animals
immunogenic
what is the gram+ve membrane like
Gram +ve bacterial have the single membrane and cell wall and Gram negative have an extra outer membrane
gram +ve stain
purple, retain first stain in the process in their thick cell walls
gram -ve stain
pink, lose first dark purple stain from their thinner cell walls when alcohol is added (going colourless), but then get re-stained by the pink second stain
what are bacterial cell walls important for
resist large osmotic pressure on cell membrane due to high internal solute concentration in cytoplasm
what do eubacteria cell walls consist of
PG – which is made of N-acetylglucosamine (G) and N-acetylmuramic acid (M), small group of amino-acids L-alanine, D-alanine, D-glutamate, and either L-lysine or DAP
what is PG sheet made of
chains of alternating M and G molecules cross-linked by the amino-acids to form a rigid sheet
Typical cell wall peptidoglycan structure in Gram negative bacteria
Peptidoglycan contains two N acetyl sugars and D & L amino-acids and is immunogenic and sensed by hosts
what can macrophage WBC make
Macrophage white blood cells can also be stimulated to produce lysozyme and kill intracellular bacteria
gram +ve bacteria example
Bacillus
gram +ve cell wall
thick and consist of 90% peptidoglycan, and 10% teichoic acid, this is negatively charged and gives the outside of the bacterial cell a net negative charge
gram -ve bacteria example
Salmonella
gram -ve cell walls
thin with no teichoic acids, they are connected to outer membrane by Braun’s lipo-protein
where is the gram -ve outer membrane
Outside cell wall in Gram-negative bacteria (special mycomembrane exists outside some Gram-positive bacteria such as Mycobacteria which cause TB)
what is the gram -ve outer membrane
lipid bilayer, only inner leaflet is solely phospholipid, outer leaflet is lipopolysaccharide (LPS)
what does the LPS consist of
hydrophobic Lipid A tails bound to a sugar core made up of heptose and KDO, this is bound to a long hydrophilic carbohydrate chain, O antigen which sticks out into the medium
what is the o antigen like
hydrophilic, excludes hydrophobic compounds from getting close to bacteria
where is LPS
only in nature in bacteria
what is LPS like
highly toxic to humans and sensed by them
endotoxin - only released when bacterial cells lyse
what is needed in gram -ve outer membrane
Because it is a membrane, special channels needed for materials to get in and out of cells - porins
what are porins
proteins in circular groups spanning membrane, form pores allowing molecules of certain size to pass into periplasm
when do porins open/close
in response to osmotic conditions
what are some porins sensed by
host immune system
how is final LPS made
by a series of enzymes that the bacteria can acquire or have extra genes for to vary it
where is the periplasm
compartment between inner and outer membranes of Gram-negative bacteria
how much of the cell does the periplasm take up
20-40% of the total cell volume
what does the periplasm contain
thin peptidoglycan wall and many proteins
what is effected by the LPS core sugar diversity in E.coli
Changes immune recognition
O polysaccharide/ O antigen also varies greatly or is absent, again changing immune recognition
what do the periplasmic proteins bind
Binding proteins for amino-acids, sugars, ions and co-factors
what enzymes do periplasmic proteins have
degradative
“Detoxifying”
what are the examples of degradative enzymes - periplasm
proteases and nucleases
what are the examples of detoxifying enzymes - periplasm
-lactamases which break-down penicillin
what continues energy production in periplasm
cytochromes
what do cytochromes do
required to keep electron-transport and therefore energy production continuing
what is Mycobacterium tuberculosis like
unusual Gram +ve bacterium
what is the layer of MB TB like
forms thick outer layers, including a special “mycomembrane”
mycolic acids
effect of thick mycobacterium - mycomembrane
gives it resilience against innate immune system
effect of mycolic acid
make a novel kind of outer membrane which helps resist damage from macrophages when the Mycobacteria are causing tuberculosis (TB)
what is the capsule like
Loose slimy layer around outside of some bacteria
hydrophilic polymer
what is capsule usually made of
sugar molecules such as fructose and glucose
what can capsule prevent
pathogenic bacterium being enveloped and destroyed by phagocytes in host defence mechanisms in blood
what may capsule allow
bacterium to attach to a surface, e.g. Streptococcus mutans which causes plaque on teeth
what senses the capsule
host immune system
how are capsules viewed - microscope
Capsules on microscope use Indian Ink Staining
Not all bacteria of one type/strain make them at any one time - a process called phase variation can invert the promoter (on/off) at a gene that controls their synthesis
where is the S-layer found
in several different bacterial species
Usually external to all other layers an alternative to a capsule
what is the S-layer like
rigid crystalline lattice composed of protein (or glycoprotein) subunits arranged in a regular array
how are the protein subunits assembled in S-layer
Protein subunits have self-assembly properties and may form sheets several molecules thick
what are S-layers resistant to
resistance to proteolytic enzymes and may protect against phage infection
what is the S-layer function
protective
Protruding structures from bacterial cell surface examples
flagella
fimbriae
related pili
what do cell membranes and gram -ve bacterium have
Flagellar motor, rotor and drive shaft
what are flagella like
Long
wavy
helical filaments
protrude from cell surface of may different bacteria
what is the flagellar arrangement
polar or peritrichous
how many flagellar are present in bacteria
variable in number depending on bacterial species
what make up the flagella
several different proteins, main body of flagellum, filament, is a hollow cylinder made up of a helical array of protein subunits. Different proteins compose other parts of the flagellum
how do bacteria swim
Flagella rotate at high speed from basal motor complexes in cytoplasmic membrane
why do bacteria need to move
swim through aqueous environments e.g. gut contents in humans or in mouth
what powers the flagellar movement
Rotation powered by ion-motive gradient across cytoplasmic membrane (usually proton gradient). Ions are thought to interact electrostatically with motor proteins to cause rotation, unknown mechanism
is ATP needed in flagella rotation
Rotation does not require hydrolysis of ATP
where do flagella filaments grow from
distal end
Self-assembly of external components of flagella occurs at the distal end of the growing flagellum, monomers being secreted from the cell and travelling up hollow centre of the flagellum
what is flagellin
main propeller protein
why are flagellin sequences varied
evade immune recognition
why do flagella evoke immune response
No known homologues in eukaryotes so evoke an immune response
what are flagella required for
- Required for many bacteria-higher organism interactions, such as host interaction reaching gut mucosa by swimming from lumen, but not essential for life
what signals define flagella direction movement
Flagellar motor- rotation drives swimming and tactic signal CheY to FliM defines direction
where do flagella swim to
Swimming = bacteria reach optimum environments for growth, or for pathogens to reach infection sites on hosts
what is in the flagellum base
proteins concerned with export of flagellar components
what does the type III exporter tip
integrates into human cell membrane, delivers effector proteins
what are the fimbriae types
Type 1 or common pili
what are fimbriae like
Straight
usually stationary
filaments protrude from surface of many bacteria
how are fimbriae proteins arranged
protein molecules arranged in a helix to form the cylindrical shape
how do fimbriae grow
New molecules are added at the base as new fimbriae grow
why is the tip in fimbriae important
Function to allow attachment of bacteria to each other or to surfaces. Specialised tip proteins on fimbriae allow binding specificity
what are the conjugative pili
sex or F pili (As some encoded by F plasmid)
what are conjugative pili like
Straight
stationary (non-waving or rotating, but retractable)
filaments which protrude from bacteria surface which carry certain plasmids
how many conjugative pili are there in each bacterial cell
one or two pili found per bacterial cell
what is a conjugative pili composed of
Composed of a cylindrical helix of protein (pilin) molecules
what does conjugative pili allow
allow attachment of 2 compatible bacteria for the transfer of genetic material
what do sex pili allow
allow bacteria to conjugate and pass their DNA around - allows many different genes to be acquired including genes for surface structure variation
what is conjugation
natural process, leads to antibiotic resistance in hospitals by gene transfer from soil bacteria to pathogens
what happens if pili are recognised
If pili recognized and bound by antibodies they can’t extrude and retract so gene transfer can’t occur
what do conjugative plasmids encode
pilus structure and transfer DNA
Bacterial Conjugation using sex pili
Bacteria come together via attachment of the E.coli sex pilus coded for by the plasmid DNA in the E.coli
Pilus retracts and cytoplasms fuse for plasmid transfer
