Midterm 1.3 Flashcards
Which bacteria (gram +/-) has interbridges? Explain its function (!)
Gram +
Helps connect different peptidoglycan layers. These are also peptide crosslinks, extended by a few amino acids
(This way provides additional strength)
Which bacteria (gram +/-) has teichoic acids? Explain its function (!)
Gram +
Provide cell strength
Help trap divalent metal ions such as Mg2+
Barrier & attachment functions
Long polymers comprised of glycerol phosphate or ribitol phosphate with attached D-glucose and/or D-alanine
Covalently attached to peptidoglycan or cytoplasmic membranes
Explain gram staining for gram + bacteria
Gram + thick layer of peptidoglycan is dehydrated - pores close and prevent escape of crystal violet dye - cells are stained purple
Explain gram staining for gram - bacteria
Decolorizing agent degrades outer membrane, thin/porous peptidoglycan layer does not retain purple stain. Cells appear pink due to safranin counterstain
Mycoplasma
Unusual bacteria that lacks cell walls
- An intracellular parasite that lives within host cell
- Minimal osmotic pressure within host cell - cells burst in low solute environments
- Specialized/unusually strong cell membrane
Lysosome
Enzyme that degrades peptidoglycan
Protoplasts/spheroplasts
A bacterial or plant cell with the cell wall removed
What is the outer membrane/leaflet of gram - bacteria composed of?
An important molecule called LPS (lipopolysaccharide)
What are the 3 parts of LPS?
- Lipid A (within membrane)
- Core polysaccharide
- O-specific polysaccharide (outermost component)
Explain the features of the lipid A
Hydrophobic tails anchor Lipid A in OM - base of LPS
Phosphates confer a negative charge
What can endotoxin lead to?
Can lead to a potent and unchecked immune response - can cause septic shock if detected in bloodstream
Why can lipid A be sensed as an endotoxin?
Lipid A is not made by humans ever, which means that if this lipid is detected in the bloodstream it means we have a bad bacteria in the bloodstream
O-specific polysaccharide
polysaccharide
Polysaccharide comprised of diverse sugar subunits connected and branched in different ways
Also called O antigen
What is the current view of outer leaflet of the outer membrane in respect to LPS and phospholipid? (!)
The outer leaflet of the outer membrane is mostly (or almost exclusively) LPS with very little phospholipid
What is inner leaflet of outer membrane composed of? How does that affect outer membrane?
The inner leaflet is comprised of phospholipid. Therefore it is asymmetrical
What is the function of Braun’s lipoprotein? (!)
Serves to connect the outer membrane to cell wall
Porins (!)
Protein channels that serve as channels for entrance/exit of small molecules
- Can be specific or non-specific
(Can remember as pores)
What are the major functions of the outer membrane?
1) Provides mechanical strength to the cell - ionic bonds between adjacent LPS molecules via divalent metal ions
2) Important barrier. Soaks up or blocks access to many molecules - important for antibiotic sensitivity
3) Protects cell wall
4) Enables a substantial periplasmic space
Periplasmic space (“periplasm”)
Space between cytoplasmic/outer membranes of gram - bacteria
Much smaller space between cell membrane and cell wall in gram + bacteria
Buffer between environment and cell
- Break down macromolecules for uptake as nutrients
- High affinity binding protein for nutrients
- Detoxify harmful compounds
- Protein folding - disulfide bond formation
S-layer
Rigid/permeable monolayer of protein or glycoprotein - self-organized into a repeating structure that encompasses the cell
Always the outermost layer of the cell
Often a protective layer
Can provide a periplasmic space or keep external proteins from accessing OM or cell wall
What is the similarity and difference between capsules and slime layers? (!)
Similarity: both are coats of polysaccharides around the cell surface
Have same function
Adhering to the surfaces, protection from host immune cells (bacterial pathogens) & protection from water loss/dehydration
Difference: Capsules are organized into a matrix and attached to the cell while slime layers are loosely attached, less organized
Group translocation
Transporter substance is bound by a transporter and is chemically modified during transport
- Phosphotransferase system (!). Glucose uptake and also transports other sugars.
- Membrane is impermeable to the phosphorylated sugar molecule - remains in cell
- Hydrolysis of PEP
ABC transporters
ATP binding cassette use ATP to power the transport of substances across the cytoplasmic membrane
- 2 ATPase domains (proteins) provide energy
- Transmembrane domain(s) (proteins) provides selective channel
- Substrate binding protein binds molecule with high affinity and delivers it to the channelc
