Lecture 5: Microbial Physiology Flashcards
isotonic
solution has the same solute
concentration on either side
hypertonic
external solution has greater solute
hypotonic
cell interior is more concentrated
in natural settings, cells are in ____ solutions
hypotonic
inside us the external fluid is very salty, creates
_____ situation
isotonic
Cells without walls will burst when placed in ______
solution
hypotonic
Cells with walls (like bacteria, plants) build up ______ pressure inside cell
turgor
turgor pressure
pressure in cell due to solute/water differences
Osmolarity
The total concentration of dissolved molecules in water
diffusion
Solutions tend toward even distribution of solutes
osmosis
the flow of water in
response to this concentration difference
Cell wall
- peptidoglycan
Sugar components: - N-acetyl glucosamine (NAG)
- N-acetyl muramic acid (NAM)
- Peptide cross-link
through NAMt - This structure is G- PG
- Penicillin antibiotics work
on cell wall synthesis
Amino Acids:
- L-alanine
- d-glutamate
- med-diaminopimelic acid
- d-alanine
PG cross-linking
Peptide cross-bridge
- Can vary from species to species
- In G- uses D- amino acids (L form used in proteins)
- In G+ uses penta-glycine
- In all cases interactions between peptide chains creates a mesh structure that stabilizes the cell against turgor pressure
Different cross-linkers
- S. Aureus murein
- E. coli murein
peptidoglycan synthesis
- PG monomer NAG-
NAM(pentapeptide) - Carried out of cell on carrier lipoprotein
- Addition to cell wall requires autolysin and
transpeptidase activity - Cut and paste new subunits
- made in cytoplasm of the cell
Gram negative-murein sacculus (cell wall)
- Thin cell wall only a few layers thick, in between
two membranes - uses L-alanine,D-glutamate,
meso-diaminopimelic acid, D-alanine
Gram positive cell wall
- a thick cell wall made up of
PG, also contains lipoteichoic acid (LTA) - Gram positive cell wall uses primarily glycine, serine, threonines
Lipopolysaccharide (LPS)
has two major components:
- O antigen repeating polysaccharide
- Lipid A (attaches it to OM)
- LPS is an endotoxin
- Lipid A component is the
causative agent of gram
negative septic shock (septicemia)
Gram negative OM
Makes cell negatively charged
Prevents entry of large molecules (antibiotics)
Porins control flow of nutrients, ions, chemicals
Allows for antigenic variation (O157:H7), immune system evasion
Gram negative periplasm
- Space in between outer and inner
membranes
Bacteria secrete many enzymes into this
space
Hydrolysis of many nutrient precursors,
harmful chemicals may occur here
Periplasmic space
Gram negative only
A great deal of biochem occurs here
OM is a prefilter for large molecules
Porins not very specific
Periplasmic proteins scavenge nutrients
PG layer is here
Many proteins are secreted into the periplasm from cytosol
Plasma membrane
- The plasma membrane is the same in all bacteria
“Fluid Mosaic” model- proteins float freely in a mobile“ phospholipid bilayer
Some proteins may be attached to the phospholipid head group
Integral membrane proteins-can only be removed by disruption of the membrane
This includes transmembrane proteins (pores)
Role of the membrane
Membrane controls flow of molecules in
and out of the cell
“Semi-permeable”
Some molecules (water, for example) flow freely through membrane pores
Other molecules are restricted, by size or charge
facilitated diffusion
a pore or channel
may allow the cell to expend energy to control this flow of molecules (doesn’t
work against the gradient, though)
