Structural Macromolecules (Dr Alderwick): Part 2 Flashcards
S-layer attachment in bacteria?
- negative: LPS associated
- positive: PG and teichoic acids
S-layer attachment in archaea?
- negative: hydrophobic anchor
- positive: psedomurein
Paracrystalline Surface Layer (S-layer_
- briefly describe what its found in..composition , arrangement etc
- in many bacteria and all major lineages of archaea
- composite of protein and glycopolymers
- ordered symmetrical appearance (self arranging)
- hexagonal, tetragonal and trimeric arrangement
What is the function of S-layer in bacteria?
- outermost layer - interaction with host
What is the function of S-layer in archaea?
- protection against osmotic pressure
- protection against permeability layer and low pH, lysozyme and other lytic enzymes, adhesion esp glycosylated s-layers, protection against phagocytosis and other biological predators
Why is the bacterial cell surface important?
- also + vs -?
- site at which bacterial cell meets enviornment
- host cell components
- adhesion - colonisation
- capsules and slime layers
- gram +: fimbriae
- gram -: fimbriae, pilus and type III - IV secretion systems
Explain the bacterial cell surface structure fimbriae!
- hair like proteinaceous appendages
- 1- 20 uM in length and 20nm in diameter
- gram neg bacteria Enterobacteriaceae and Neisseria gonorrhoeae
- no motility function ****
- antigenic and hemagglutinating properties - adherence to cells
Explain the bacterial cell surface structure pilus
- longer than fimbriae
- serves to connect the bacteria to those of the same species, different species and host cells
- made of an oligomer pilin
- various types of this oligomer
- Type IV pili = adhesion..surfaces, bacteria (colinsation and biofilm)
- Sex pili: conjugation sex…transfer of plasmid DNA between species or across species…this transformation can lead to antibiotic resistance
Difference between gram + and - pilus?
- neg: pilin molecules attached via protein-protein interactions
- pos: polymeriszed pilin appendage
- *assembly is tightly regulated
With the bacterial operon what are the two regions involved in pilus assembly. Explain them briefly
- syntenic region: aka constant region –>these gene clusters are seen across many species and are very conserved (found in basal area)
- variable regin: for the tip fibrium - these are highly variable and not conserved. Species specific thereby making them different from one another.
Describe the bacterial pilus assembly pathway
- Chaperone-usher pathway
- SEC system
- PapD= Chaperone
- PapA, K, E, F and associated with PapD
Explain bacterial conjugation
- donor and recipient cell
- line up
- sex pili attachment occurs
- DNA cleavage
- linerisation of DNA
- DNA transfer
- DNA polymerase > re-circulation of DNA
Explain briefly the mechanisms of bacterial motility! (archaea comparison)
- flagella (primary role locomotion )
- Bacterial: proteinaceous helical appendages
- Archaeal: superficially similar to bacterial counterparts
- *SHARE NO SEQUENCE HOMOLGY WITH BACTERIAL PROTEINS AKA THEY EVOLVED DIFFERENTLY
Describe bacterial flagella !
- long thin appendage: 15-20 nm in diameter ( largest app found)
- attach in various cellular locations that are species specific
What are the three cellular locations bacterial flagella can be in?
- Peritrichous -> developing all over the surface of the bacteria
- Polar -> one long one at one end
- Lophotrichous –> cluster of them at one end
Flagella experiment with Rhodospirillum centenum revealed what about them?
- when grown in liquid media it had a polar flagella
- in solid media it had peritrichous flagella
- arrangement is dependent on the enviornment and it can adapt locomotion abilities
What drives flagellar rotation?
- proton motive force
- simple transport : driven by the energy in the proton motive force
- *electrochemical gradient
Describe the structure of the flagella?
- L ring: located in the outer membrane
- P ring:located in the peptidoglycan
- MS ring: located in the cytoplasmic membrane
- C Ring: located in the cytoplasm
- 45 degree hook allows it to push through the enviornment!
What is a Type III secretion ?
- protein appendage found in only Gram negative bacteria
- needle like structure
- probe: sensory function to detect host organisms
- secrete: inject effector proteins which signal the host cell to engulf the bacterium and tamper with the host cell cycle machinery
Structure of Type III secretion complex?
- similar to the flagella
- evidence of evolution ??
T3SS-> Flagella
LPS
OM
Peptidogylcan
IM
Base= the above three
Magnetotactic bacteria ?
- discovered when?
- how do they orient themselves?
- move in response to?
- major function is??
- magnetic bacteria
- discovered in 1975
- orient themselves along the magnetic field lines of the earth
- move in response to environments magnetic characteristics –> Magnetotaxis
- *major function is unknown
Magnetotactic bacteria :
- contain what?
- magnetosome forms via?
- many species grow best where?
- intracellular particles called magnetite- crystals of Fe3O
- magnetosome form via a specialized invagination of the cytoplasmic membrane
- magnetic dipole exerts this
- many species grow best at low O2 concentrations
- drives this aquatic cells downward towards low lying sediments
