the microbial cell Flashcards
what are the different shapes of bacteria and their associated names
1) spherical= coccus
2) rodshaped= bacillus
3) spiral shaped = spirillum
what is the functions of the prokaryotic cell envelope
- maintains shape
- provides protection
- prevents bursting or rupture in hypotonic environments
outline the structure of the prokaryotic cell envelope
- cell membrane
- cell wall
- outer membrane which is only present in gram negative bacteria
why is the cell membrane not enough to protect prokaryotes
the lipid nature makes the cell membrane vulnerable to chemicals so often they surround the cell membrane with tough cell wall
outline the structure or formation of the cell wall
- made up of murein
- glycan chains made up of N-acetylglucosamine and N-acetyl muramic acid connected by beta 1-4 glycosylic bonds
- these form crosslinked with other chance via small peptides
outline what a gram positive cell is
the cell membrane is surrounded by a thick cell wall made of murein
absence of an outer membrane
- teichoic acids provide rigidity and help bacteria adhere to surfaces
what do beta lactam antibiotics do
inhibit peptidoglycan/murein synthesis
outline the process of b-lactams acting on bacteria
1) bind to and inactivate the enzyme which assembles the murein chains and bonds the peptides of the layers together
2) with no active enzyme the cell wall cant be remodelled as it grows
3) the cell wall weakens causing internal osmotic pressure to cause the cell to burst
outline the structure of a gram negative cell
a thin layer of murein as well as the presence of an outer membrane made up of lipopolysaccharides
what is the lipopolysaccarhide membrane made up of
1) one glycolipid
2) a polysaccharide core
3) a long carbohydrate chain
what is an O antigen
an antigen made up of varying numbers of repeating units which is very immunogenic and redners addtional protection from certain antibiotics
what are porins
protein channels in the membranes of gram negative bacteria which mediates the diffusion of hydrophilic compounds
what is the periplasm
a gel like space between the cell membrane and the outer membrane where the murein layer is found
what does the periplasm contain
1) degradative enzymes which break down molecules so they can be transported across inner membrane
2) proteins
3) beta lactamases which protect the cells by inactivating antibiotics
what are mycolic acids
alternatives in some bacteria to cell walls- a wax of 60-90 long fatty acids which orientate themselves into lipid bilayers
what are acid fast bacteria
bacteria with an outer membrane made of mycolic acids
outline the characteristics of acid fast bacteria
more resistant to harsh chemicals and desiccation as the membrane is very hydrophobic
outline the process of acid fast staining for identification
1) stain with carbol fuchsin in presence of heat
2) was with a mixture of acid and alcohol to decolourise all but acid fast cells
3) counter stain with methylene blue to show non acid-fast cells
what are mycoplasmas
bacteira which do no have a cell wall only a cell membrane and have sterols in the membranes to make them more rigid
what are capsules/slime layers
a layer made up of high-molecular polysaccharides or polymers of amino acids
when attached to the cell= capsule
when loose = slime layer
outline the structure of a flagellum
1) a long helical filament
2) a connecting hook
3) a basal body equipped with a rotor to turn flagellum
outline the structure of the filament of the flilament
a helical rigid hollow composed of a protein called flagellin
very antigenic
outline the structure of the hook of the filament
a joint betwen the filament of the basal body and filament made of a hook protien
outline the structure of the basal body of the filament
a rod attached with rings which anchors the structure to the cell envelope allowing the rod to roate
what are pili
hair structures which allow the cell to attache to hosts and surfaces to transfer proteins and move
what proteins make up pili
pilins
outline pili twitching mobility
1) pili extend and retract by adding or removing the pilin protein to the base of the pili
2) pili touches surface and he adhesins in the tip adhere
3) the pilus depolymerizes the base shortening the pilus dragging it forward
