CELS 191 Lecture 28 Flashcards
(26 cards)
how is DNA stored in bacteria
in a nucleoid (a defined region of the cell) as a single circular double stranded chromosome
what are plasmids
small circular self-replicating DNA molecules found in the cytosol of bacteria (seperate from the main chromosome)
what do plasmids allow for
genetic transfer
what is the function of the bacterial cell wall
it is a rigid macromolecule later that provides strength to cell shape and protects cells from osmotic lysis and confers cell shape
what are prokaryotes that lack cell walls called
mycoplasma - a group of pathogenic bacteria
what is transpeptidase
an enzyme in cell walls that cross linked the peptidoglycan chains to form rigid cell walls
what is the structure of peptidoglycan
a carbohydrate backbone made of alternating NAG and NAM units cross linked with amino acids cross bridges and side chain amino acids to hold together the layer of carbohydrates
what is the method to perform a gram stain
application of crystal violet dye
application of iodine (mordant)
alcohol wash (decolorisation)
application of safranin (counterstain)
what colour are gram positive bacteria after a gram stain has been performed
purple
what colour are gram negative bacteria after a gram stain has been performed
pink
what is responsible for the differences in gram stain reaction between gram positive and gram negative bacteria
structural differences between cell walls
what is the composition of the cell wall of a gram positive bacteria
a thick (20-80nm) peptidoglycan layer sitting outside the plasma membrane
what is the composition of the cell wall of a gram negative bacteria
a thin layer (5-10nm) of peptidoglycan sandwiched between and outer and inner membrane
what does the outer membrane of a gram negative bacteria contain
lipopolysaccharides (LPS)
what do motile bacteria produce
flagella - long flexible appendages resembling tails 10-20nm in diameter that act like propellers allowing the cell to rotate through a liquid medium
what is chemotaxis
when bacteria move along a concentration gradient towards a chemical attractant (positive) or away from a chemical repellent (negative)
what is the function of fimbriae - also called adherence pili or adhesins
these are structures with adhesive properties that cause bacteria to stick/adhere to surfaces
how are fimbriae different from flagella
they aren’t involved in motility and they are much shorter (1micrometer) and more numerous (100-1000 per cell)
what are pilli
structures that allow for the attachment to other bacteria and the transfer of genetic material via conjugation
what is glycocalyx
a gelatinous polysaccharide and or polypeptide outer covering that forms a sticky meshwork of fibres
what is it called when glycocalyx is organised into a defined structure attached firmly to a cell wall
a capsule
what is it called when glycocalyx is disorganised without cell shape attached loosely to the cell wall
a slime layer
what functions can capsules serve
virulence factors - protecting bacteria from phagocytes and engulfment by immune cells
prevent the cell from drying out (desiccation)
what are bacterial endospores
spores formed during unfavourable growth conditions that germinate under favourable conditions - this protects the cells from stress
