Cell surface reactivity Flashcards
what does a cytoplasmic membrane do
separates the inside of the cell from the outside - lots of enzymes involved in metabolism reside here
what do bacterial cell walls
contain peptidoglycan (polymer of polysaccharides linked by proteins)
what is outside the cell wall
- capsule
- EPS
- sheaths
- S-layers
cell wall + stuff outside the cell =
cell envelope
what is EPS (extracellular polymeric substances)
mostly made up of polysaccharides, produced inside the cell and excreted through the cell wall
what is EPS the same as
the capsule
making EPS requires lots of energy but it is worth it because it can be used as:
- Protection from desiccation, pH or temperature fluctuations
- Adherence to surfaces and stability of the colony
- Are an energy and carbon reserve
what is a sheath
they act like a sieve, protecting from large molecules - they have a different surface charge than the cell, acting as a mediator between cell and environment
what are sheaths made of
methanogens
some cyanobacteria
some Fe- and Mn- oxidisers
what are S-layers
structured layers - they are more organised than EPS or sheaths - paracrystalline - they have a similar role to sheaths
what is a functional group
specific group of atoms or bonds within organic molecules that are responsible for the characteristic reactions of those molecules
what controls the behaviour of most functional groups
pH of environment
what is the phZPC
the pH of zero point of charge
what is the phZPC for most bacteria
pH 2-4
what happens at low pH
surface functional groups are fully protonated, average bacteria surface is neutral or positively charged and hydrophobic
what happens at high pH
functional groups are deprotonated, average bacteria surface is negatively charged and hydrophilic (increases with increased pH)
most bacteria grow at circumneutral pH meaning…
most bacteria surfaces are negatively charged
why might cell surfaces with sheaths, S-layers and EPS have more complex charge distributions
because these layers can have different compositions and therefore different chrges
Because most cells have low pHZPC and therefore mostly negatively charged…
they have a tendency to adsorb cations - especially metal cations
what are the 3 steps of colonization of surfaces
- Transport of bacteria to a surface
- Initial adhesion via electrostatic attraction
- Irreversible attachment via excretion of EPS or appendages
