Week 3 - Bacterial Physiology Flashcards
Gram -ve inner membrane
Has an outer membrane, and a thin layer of peptidoglycan followed by the periplasm and then the cytoplasmic membrane
Gram +ve inner membrane
Have a thick layer of peptidoglycan and attached to the peptidoglycan are sugars such as teichoic acid and lipoteichoic acid.
Peptidoglycan Structure
- found in all bacteria with a cell wall.
- made from polysaccharides N- Acetylglucosamine and N- Acetylmuramic acid
- the sugars and amino acids are connected by glycosidic and peptide bonds
- has Beta 1,4 link which can be destroyed by lysozyme
- Lysine, DAP (-) and ornithine are the amino acids used to form interbridges
Peptidoglycan facts
Gram -ve: thin. 2-7nm. Located between inner and outer membrane
Gram +ve: thick. 20-35nm. Located outside the plasma membrane.
- particles less than 2nnm can pass freely though peptidoglycan layer, others need a protein channel.
( Na+, H20, mono & disaccharides, lysozyme, ATP)
Teichoic Acid
Found only in gram +ve bacteria.
These are long polymers of sugar alcohol and long phosphate repeating units.
sugar alcohols are reduced (OH) while sugars are not.
-protects bacteria from host defense system
Gram Negative Outer Membrane
- asymmetric
- inner: phospholipids
outer: lipopolysaccharides (Endotoxin)
LPS has 3 main layers
Lipid A- attaches to the outer membrane. Has 2 glucosamine residues with lipids attached. Conserved among species.
Core- Has KDO & HEP sugars. Conserved among species.
O-specific: Has species specific sugars. Variable and not found in all bacteria.
Lipopolysaccharide Biosynthesis
the LPS core and O-antigen, but both are made in the cytoplasm.
use of ATP hydrolysis
O antigen is made on undecaprenyl pyrophosphate, in the cytoplasm.
A protein then flips the o-antigens to the periplasmic side.
More proteins help polymerize the o-antigen.
the core is made directly on the lipid A, an ABC transporter helps flip the molecule to the periplasmic side
another protein uses energy of the di-phosphates to help attach the o-antigen to the lipid A core
finally an ABC transporter helps move the LPS to the outer leaflet of the membrane
Lipopolysaccharides
Endotoxin
Contributes to negative charge of cell
Helps stabilize outer membrane
helps with attaching to surfaces
creates permeability layer
o-antigen protects from host defense systems
Prorins
Help make outer membrane permeable
b- barrels
found mostly in gram -ve bacteria
trimeric
S- layers
Crystal line latice of glycoproteins
not common in bacteria
self assemble into 2D sheets that attach to the LPS or peptidoglycan
protect against bacteriophage, low ph and lytic enzymes
Capsules & Glycocalyx
thick polysaccharide layers present on the surface of bacteria
not part of the cell wall.
Types of Capsules & glycocalyx
- LPS/teichoic acid/ S-layer glycans
- Alignate
- poly N- acetylglucosamine
- Enterobacterial common antigen
- cellulose
Secretion Systems
Multi-protein spanning complexes. There are different types of protein complexes which allow for transport in and out of the cell.
Pili
Thin filamentous structures made of glycoproteins.
They extend from the cell surface, and are found in all gram -ve bacteria and in some gram +ve bacteria.
These pili are retractable and can go in and out of the bacteria.
The pili help with attachment of pathogens to the host tissue,
used in conjugation for DNA transfer.
Types of Pili
Fimbrae- adherence: help attach bacteria to a surface
Conjugation- exchange: exchange genetic material, and transfer DNA
Electrically conducive Pili - Transfer of electrons/ metabolism
Type 4 pili - used for twitching motility
Type IVa Pilus Structure
The pilus helps with adhesion and twitching
The pilus is built from the bottom up using a motor. The protein extends from the inner membrane, is anchored in the peptidoglycan by a ring and extends into the outer membrane where the pilus is. The pilus is made up of individual proteins. The pilus will attach to an object and the proteins connected to it retract which cause a pulling motion.
The pilus motor, uses ATP to spin. The direction that the motor spins determines if the pilus is getting built up or broken down.
Twitching
Motility on a solid surface.
Using the type 4 pili, and ATP hydrolysis, the pili is extended attached to the solid surface and is retracted. These steps cause movement.
Gliding
motility on a solid surface.
The bacteria rotate and spin forward. Using the PMF, adhesion proteins and gliding motors to move.
Swarming
motility on a semi-solid surface
Fast, coordinated movement of cells that is mediated by flagella. Usually patterns are formed. Bacteria move together/ communicate this causes them to form patterns.
Bacterial Flagella
Flagella are thin hollow appendages they help with swarming ( semi-solid) and swimming ( liquid). The powered rotation of flagella moves bacteria.
Flagella use the proton motive force to move. The protons go through the motor proteins. The flagellum motor has the rotor and the stator. The rotor has the filament, hook, and rod. The stator has the Mot AB proteins
Peritrichous
Flagella around the cell surface
CCW rotation means flagella swim in a straight line and move forward. CW rotation means they tumble randomly in all directions.
Polar
Attached at the ends of the cell
CCW rotation means the flagella run in the forward direction. CW rotation means the flagella go in the reverse direction
Lophotrichous
Group of flagella at one end
Unidirectional flagella only run CW
Bacterial Flagella Biosynthesis
Flagella grow from the tip.
They grow from the cytoplasm to the outer membrane.
The MS ring is made first followed by the mot proteins, P ring, L ring and the early hook.
The Late hook has the cap proteins which help the flagellin (protein) form into the filament.
Flagellin is made in the cytoplasm and pushes up through the hook to create the filament.
The base of the flagellum is embedded in the peptidoglycan so its sturdy.
