2.4 gram neg and acid fast cell walls Flashcards
(31 cards)
between the cell membrane and the outer membrane of gram negative is a region called the
periplasma space.
periplasma space
spans the peptidoglycan layer, and is made of gel called periplasm, contains water, nutrients, and substances secreted by the cell.
what substances are secreted by the gram - cell for the periplasma space
digestive enzymes and proteins involved in specific transport.
why is the peroiplasm the perfect place to store the enzymes secreted by the cell
the outer membrane prevents the enzymes from leaching away from the cell.
why are the ezymes secreted by the gram neg cell important
they catabolize large nutrient molecules that have been brought through the outer membrane into smaller molecules that can be absorbed and transported into the cell/
what is the gram negative peptidoglycan composed of
same components as gram positive – alternating NAM and NAG – difference is that the gram neg lacks the pentapeptide cross bridges.
– tetrapeptides cross-link by forming interpeptide bonds between DAP on one chain and D-ala on the other chain
why cant penicillin and lysozyme affect gram negative bacteria
they are not able to penetrate the outer membrane – these agents do not have access to the gram negative’s peptidoglycan.
thickness of peptidoglycan in gram negative bacteria
much thinner than gram positive (7-8nm)
gram negative outer membrane
outer LEAFLET of outer membrane is studded with LPS (lipopolysaccharide) – a union of lipid with sugars, porins (which are spanned across whole outer membrane) – different from cytoplasmic membrane because of the presence of Lipid A
– inner leaflet of pouter membrane is composed of the same type of phospholipids as the cytoplasmic membrane
lipoprotein – what does it do
connects the outer membrane to the periplasmic space (peptidoglycan)
Lipopolysaccharide (LPS) composed of three parts
Lipid A, core polysaccharide, and O-specific polysaccharide
what is LPS also known as
endotoxin or pyogene
‘endotoxin’ because embedded in membrane and is toxic to eukaryotic cells
‘pyogene’ because it elicits fever
Lipid A
lipid portion of LPS.
– anchors the LPS in the outer membrane
– consists of two covalently attached phosphorylated glucosamine sugars that have attached to them a number of fatty acids
– lipid A is covalently attached to one of the core polysaccharide KDO sugars.
core polysaccharide
consists of 2 or 3 KDOs, 3 phosphorylated 7 carbon sugars, then some 6 carbon sugars.
O polysaccharide – O antigen
composed of hexose sugars.
modifcations of the O antigen play role in two stages of infection process
colonization/adherence, and ability to bypass host defense mechansisms
what are lipid A and the core polysaccharide attached to
O antigen
functions of LPS
- grants negative charges and repels hydrophobic molecules
- binds to divalent cations (Mg2+)
- repels fat soluble molecules such as bile that the gallbladder secretes
- prevents passage of some antibiotics.
Lipid A functions
confers toxic activity by elicitin strong immune responses in mammals
what acts as determinants of virulence in gram negative bacteria
Lipid A (toxic component) and the O polysaccharide (non toxic but immunogenic portion of LPS)
how does Lipid A infect cells (think what happens after a cell dies)
when gram- cell dies, it releases LPS when its cell wall disintegrates.
- the hydrophilic O polysaccharide acts as a water soluble carrier for. the toxic lipid A. free lipid A can trigger fever and an immune response.
what would happen during an infection in your bloodstream?
bloodstream has millions of bacterial cells that have LPS.
– remember LPS is toxic
– if an antibiotic treatment killed these gram- cells, they would release a lot of lipid A, which will trigger an immune response that might threaten the patient even more than live bacteria.
– it is better to treat these infections with antibiotics that halt the REPLICATION but dso not actually kill the cells
– that way the immune system has time to engulf bacteria before they release lipid A and thereby contain it.
acid fast bacteria ; mycobacteria
cells have an additional sugar layer.
what is the additional sugar layer of acid fast bacteria called
arabinogalactan – covalently attached to the peptidogycan layer and attached to the arabinoglactan long chain mycolic acids
