Micro 1- cell structure and classification Flashcards
creation of the three domain system
developed by worse in 1978, based on sequence of nucleotides in rRNA
what are the 3 domains
- eukarya (animals, plants, fungi, protists)
- bacteria
- archaea
vertical gene transfer
passed down generation to generation
horizontal gene transfer
occurs within the community of early cells (not associated with offspring)
important characteristics of prokaryote
-one circular chromosome, not in a membrane
-no histones
-no organelles
-divides by binary fission
cell walls: peptidoglycan in bacteria, pseudomurein in archaea
important characteristics of eukaryotes
- paired chromosomes in nuclear membrane
- histones
- organelles
- polysaccaride cell walls, when present
- divides by mitosis
size, shape, and arrangement of bacterial cells
average size: 0.2 to 2.0 um diameter
- most bacteria are monomorphic (single shape)
- a few are pleomorphic (many shapes)
list of shapes of cells
- bacillus
- coccus
- spiral
- star-shapes
- rectangular
bacillus
rod shaped
coccus
spherical
3 types of spiral shapes
vibrio- slightly curved
spirillum- helical, rigid
spirochete- helical, flexible
when cells are arranged in pairs
diplococci, diplobacilli
when cells are arranged in chains
streptococci, streptobacilli
when cells are arranged in clusters
staphylococci
when cells are arranged in groups of four
tetrads
when cells are arranged in tubelike groups of eight
sarcinae
list of structures external to the cell wall
- glycocalyx
- flagella
- axial filaments
- fimbriae
- pili
glycocalyx
external to cell wall, viscous, gelatinous polymer made of polysaccaride and/or polypeptide
two types of glycocalyx
- capsule: neatly organized and firmly attached
- slime layer: unorganized and firmly attached
how does glycocalyx contribute to virulence
- capsules prevent phagocytosis (by WBCs)
- extracellular polymeric substances (EPS) helps form biofilms
flagella
filamentous appendages external of the cell
- propel bacteria
- made of protein flagellin (rotates around hook)
3 parts of flagella
- filament
- hook
- basal body (this attachment different in gram- or gram+)
what does flagella allow bacteria to do
flagella allow bacteria to move towards or away from stumble (taxis)
- chemotaxis for chemical stimulus
- phototaxis for light stimulus
axial filaments
endoflagella
- found in spirochetes
- anchored at one end of a cell and extend throughout organism
ex: treponema pallidum
axial filaments used to
rotation causes cell to move like corkscrew
ex: treponema pallidum
fimbriae
hair like appendages that allow for attachment
- adhere to surfaces
- involved in forming biofilms
example of how fimbriae work
in neisseria gonorrhoeae, fimbriae helps it colonize mucous membranes- allows this organism to be virulent because it can adhere
fimbriae versus flagella
similar but fimbriae is shorter, thinner, and straighter
pili versus fimbriae
pili usually longer than fimbriae
pili
-one or two per cell, involved in motility (gliding and twitching)
pili: gliding vs. twitching
- gliding: myxobacteria (smooth)
- twitching: pseudomonas aeruginosa, neisseria gonorrhoeae and some strains of E. coli
conjugation pili
are involved in DNA transfer from one cell to another
- antibiotic resistance
- digest medium more efficiently
purposes of the cell wall
- protects the cell membrane
- prevents osmotic lysis
- maintains shape of bacterium (semi-rigid structure)
- serves as point of anchorage for flagella
- contributes to pathogenicity
cell wall in bacteria
made of peptidoglycan (sugar and protein)
complex, semi-rigid structure
peptidoglycan is
a polymer of a repeating disaccharide in rows
-NAG and NAM (2 types of sugars involved)
linkage in peptidoglycan
rows are linked by polypeptides
- tetrapeptide side chains
- peptide cross bridges
how does penicillin affect linkage in peptidoglycan
penicillin interferes with final linking and results in weakened cell wall and cell undergoes lysis
gram + cell wall
- thick peptidoglycan
- teichoic acids
gram - cell wall
thin peptidoglycan
- outer membrane (2nd cell membrane)
- periplasmic space
gram + cell:
composition of teichoic acids
- lipoteichoic acid and wall teichoic acid
- carry a negative charge
- regulate movement of cations
- provide antigenic specificity
gram - cell:
3 parts of outer membrane
- lipoproteins
- phospholipids
- lipopolysaccharides (LPS)
what does the outer membrane of gram - cell do
- protects from phagocytosis and complement
- provides barrier to antibiotics and lysozymes
LPS- lipopolysaccharides in gram - outer membrane have
- O polysaccharide: antigen recognizing molecule
- lipid A: endotoxin- causes symptoms of fever, etc.
gram staining mechanism crystal violet
in gram +, alcohol dehydrates peptidoglycan, CVI crystals do not leave
in gram -, alcohol dissolves outer membrane and leaves holes in peptidoglycan, CVI washes out, cells are colorless, safranin added to stain cells
steps of gram stain
- crystal violet purple dye
- iodine (mordant)
- alcohol wash (decolorization)
- safranin (counterstain)
atypical cell walls stain
because gram stain not effective, use acid-fast cell wall stain (carbolfuchsin)
example organisms:
-mycobacterium
-nocardia
acid-fast cell walls
- no cell walls or very little material
- waxy lipid (mycelia acid) bound to peptidoglycan
