Lecture 27: introduction to Prokaryotic cells Flashcards
the cell wall of bacteria is…
peptidoglycan
function of Bacteria cell wall:
- rigid macromolecular layer that provides strength to cell
- protect cell from osmotic lysis and confers cell shape
prokaryotes that lack cell walls are…
mycoplasmas
what are mycoplasmas?
group of pathogenic bacteria
peptidoglycan is in a…
mesh-like structure
Transpeptidase is…
the enzyme that cross-links the peptidoglycan chains to form rigid cell walls
the structure of peptidoglycan:
- NAG/NAM
- side chains amino acids
- cross bridge amino acids
gram stain procedure produces:
- gram-negative bacteria in red
- gram positive bacteria in purple
gram stain procedure:
step 1 -
application of crystal violet (purple dye)
gram stain procedure:
step 2 -
application of iodine (mordant)
gram stain procedure:
step 3 -
alcohol wash (decolorisation)
gram stain procedure:
step 4 -
Application of safranin (counterstain)
Structure of a gram-positive bacteria cell wall:
- cell wall (peptidoglycan layer)
- plasma membrane
the peptidoglycan layer in gram-positive bacteria is…
thick
thick peptidoglycan traps…
crystal violet, which masks the red safranin dye
structure of a gram-negative bacteria cell wall:
- cell wall (outer membrane/peptidoglycan)
- plasma membrane
the peptidoglycan layer in gram-negative bacteria is…
thin
in the thin layer of peptidoglycan crystal violet is…
easily washed away, revealing the red safranin dye
motile bacteria produce…
flagella
flagella are long flexible…
appendage resembling “tails”
flagella act like…
a propeller, cell rotates them to move through a liquid medium
number and location of flagella on a cell…
can very
3 Major sections of flagella:
- long filament
- hook
- basal body
long filament structure of flagellum:
- extends into surrounding medium
- composed of subunits
(protein = flagellin)
Hook structure of flagellum:
- curved section connecting the filament to the cell surface
basal body structure of flagellum:
- anchors flagellum into cell membrane
how are flagellum anchored into the cell membrane:
by special disc-shaped structures called plates or rings
tactical response moving in response to environment
chemotaxis
positive chemotaxis:
bacteria move along concentration gradient towards a chemical attractant
negative chemotaxis:
bacteria move away from a chemical repellent
temporal gradients are:
change in chemical concentrations outside the cell over time
Bacterial adherance factors:
glycocalyx
- capsules
- slime layers
glycocalyx is a…
- gelatinous polysaccharide
- or polypeptide outer covering
glycocalyx forms a…
sticky meshwork of fibres
glycocalyx organised into a defined structure attached firmly to cell wall is…
capsule
glycocalyx disorganised without cell shape, attached loosely to cell wall is…
slime layer
glycocalyx capsules can serve numerous functions including:
- virulence factors
- adhere to cell surfaces and structures
- prevent cell from drying out (desiccation)
virulence factors is:
protecting bacteria from phagocytosis and engulfment by immune cells
example of capsule adherence:
to medical implants and catheters
bacterial endospores are formed during…
unfavourable growth conditions
bacterial endospores germinate under…
favourable conditions
bacterial endospores protects cells from…
stress
bacterial endospores are only present in…
some gram positive bacteria
- members of the genus bacillus
endospores are…
highly differentiated cells
endospores are resistant too:
- heat
- harsh chemicals
- antibiotics
- disinfectants
- radiation
endospores can stay dormant…
for a very long time
