Cell Surface Reactivity Flashcards
What are the two things that make up the outer cell structure?
- Cytoplasmic membrane
2. Bacteria cell wall
What is the purpose of a cytoplasmic membrane?
Where metabolic processes for respiration and photosynthesis occur.
Separates the cytoplasm inside the cell from the outside.
- Made up of phospholipid bilayer (hydrophilic head, hydrophobic tail)
- Location of ETC
- Lots of enzymes
What makes up bacteria cell walls?
Peptidoglycan
Cells can also excrete stuff outside of cell walls e.g., capsules, EPS, sheaths and S-layers.
What does the cell envelope consist of?
Cell wall + extra stuff excreted outside cell wall
What is EPS made of and whats its role?
Made of polysaccharides, 99% water.
Produced inside the cell and excreted outside.
Type of EPS depends on environmental conditions which it will protect/ buffer cell from.
Can also help organisms attach to the cell.
What is the role of Sheaths?
Act like a sieve, protecting the cell from larger molecules.
Can have different surface charge to the cell.
What is the role of S-layers?
Similar role to sheaths.
Can shed encrusted S-layers, as made from paracrystalline layers.
What is the definition of a functional group?
Specific groups of atoms or bonds within organic molecules that are responsible for the characteristic reactions of those molecules.
What charge do fully protonated functional groups have?
Neutral or Positive
What charge do de-protonated functional groups have?
Negative or Neutral
What does ionisation of functional groups in cell walls cause?
Gives microbial surfaces an electrical charge.
Generally get overall net negative charge of cells.
What is the isoelectric point?
the pHZPC (pH of zero point charge).
pH = pHZPC when net surface charge = 0
What is the pHZPC for most bacteria?
2-4
What are the characteristics of cell surfaces at low pH?
Surface functional groups are fully protonated.
- Neutral or +vely charged
- Hydrophobic
What are the characteristics of cell surfaces at high pH?
Above pHZPC
Surface functional groups are deprotonated.
- Negatively charged surface
- Hydrophilic
Most bacteria grow best at pH above the pHZPC, so usually negatively charged.
Why do metal cations adsorb to cells?
Most cells have low pHZPC, so are negatively charged
Hence have a tendency to adsorb cations
How do metal adsorb to cells?
Metals can diffuse into EPS and bind to negatively charged or neutral functional groups.
Active process.
Capsules protect the cell from metal toxicity.
What allows for adhesion and attachment of cells?
Colonisation
What are the three processes in colonisation of cells?
- Transport bacteria to a surface
- e.g., by diffusion - Initial adhesion via electrostatic attraction
- held 5-10nm from surface
- triggers production of EPS - Irreversible attachment
- Via EPS excretion or appendages (hyphae)
- Bridges gap between cell and surface
End up with colony of cells that live within a biofilm, helping them stick to a mineral surface.
