ch 3 bacterial cell structure Flashcards
cocci
spheres that can be single or can be associated in arrangements that is useful for identification
diplococci
arise when cocci divide and remain together to form pairs
streptococci
divide on 1 plane to form long chains
staphylococci
divide in random planes making grape-like clusters
bacilli
rod shaped
differ considerably in their length-to-width ratio
coccobacilli - short and wide
vibrios
comma shaped
spirilla
rigid spiral shaped
spirochetes
flexible sprial-shaped
mycelium
network of long filaments (hyphae)
pleomorphic
organisms that are variable in shape
size-shape relationship
cells want a high surface area-to-volume ratio
- increases efficiency of nutrient uptake and diffusion of molecules within a cell
- large size and odd shape may be protective mechanisms from predation
cell envelope
plasma membrane and all the surrounding layers external to it
plasma membrane
most important of cell envelope
encompasses the cytoplasm and defines the cell
responsible for much of the cell’s relationship with the outside world
- selectively permeable barrier
- detects and responds to surrounding chemicals
- transport systems used for nutrient uptake
- metabolic processes
amphipathic
structurally asymmetric with polar and nonpolar ends
hopanoids
hydrophobic rigid planar structure similar to cholesterol
functional membrane microdomains
platforms for protein complex assemble
bacterial lipids
- plasma membrane is mainly composed of phospholipids
- have hopanoids
- distort the bilayer, which impacts the fluidity and shape in the membrane region
- form functional membrane microdomains
six macronutrients required by bacterial cells
carbon
oxygen
hydrogen
nitrogen
sulfur
phosphorus
growth factors
organic compounds that must be supplied in the diet for growth because they are essential cell components or precursors of such components and cannot be synthesized by the organism
4 transport mechanisms
passive diffusion
facilitated diffusion
primary and secondary active transport
group translocation
passive diffusion
molecules move from a region of higher conc to one of lower conc
- large conc gradient required for adequate nutrient uptake
- H2O, O2, CO2 easily cross the plasma membrane
facilitated diffusion
movement across the plasma membrane with the assistance of transport proteins that are either channels or carriers
- direction of movement is from high to low conc
- no energy required
active transport
transport of molecules against the conc gradient
- energy dependent process
group translocation
energy dependent transport that chemically modifies the molecules as it is brought into the cell
- phosphoenolpyruvate: sugar phosphotransferase system
why is uptake of ferric iron difficult
it is very insoluble
sideophores
secreted by bacteria and complex with ferric iron for transport into cell
cell wall
layer that lies just outside the plasma membrane
- helps maintain cell shape
- protect the cell from osmotic lysis
- protect the cell from toxic substances
- contribute to the ability of a pathogen to cause disease
peptidoglycan
rigid structure lying outside the plasma membrane
crosslinked by peptides for strength
gram positive cell wall
stains purple
thick peptidoglycan
may also contain teichoic acids
gram negative cell wall
stains pink or red
thin peptidoglycan and outer membrane (composed of lipids, lipoproteins, lipopolysaccharides
peptide interbridge
a short chain of amino acids linking the stem peptide of one peptidoglycan strand to that of another
teichoic acids
polymers of glycerol or ribitol joined by phosphate groups
- negatively charged
- help create and maintain structure of the cell envelope by anchoring the wall to the plasma membrane
- protect from harmful substances during cell division
- bind to host cells, initiate infectious disease process
periplasmic space
space btw plasma membrane and cell wall
periplasm occupies this space
- contains enzymes, transport proteins
lipopolysaccharide
a molecules containing both lipid and polysaccharide found in the outer membrane of the typical gram-negative cell wall
consists of three parts:
- lipid A - buried in outer membrane, contains two glucosamine sugar derivatives
- core polysaccharide - joined to lipid A and is constructed of 10 sugars
- O side chain (O antigen) - polysaccharide chain extending outward from the core
functions of LPS
- contributes to the negative charge on the bacterial surface bc the core polysaccharide usually contains charged sugars and phosphate
- it helps stabilize outer membrane structure because lipid A is a major constituent of the exterior leaflet of the outer membrane
- it helps crate a permeability barrier
- helps protect pathogenic bacteria from host defenses
- lipid A can act as a toxin (endotoxin)
porins
proteins that form channels across the outer membrane of typical gram-negative bacterial cell walls through which small molecules enter the periplasm
- facilitated transport
two step process of transport into a gram-negative cell
- the solute crosses the outer membrane into the periplasm (by porins)
- crosses the plasma membrane
plasmolysis
water flows out of the cell and the cytoplasm shrivels up
- solute conc outside cell is greater than inside
hypertonic environment
lysis
water moves into the cell and cell swells and bursts
- solute conc outside cell less than inside the cell
hypotonic solution
lysozyme
attacks peptidoglycan by hydrolyzing the bond that connects N-acetylmuramic acid with N-acetylglucosamine
evidence of protective nature of peptidoglycan
- lysozyme breaks bond btw peptidoglycan
- penicillin inhibits peptidoglycan synthesis
when cells treated with either of the above, they lyse in a hypotonic solution
mycoplasma
lack a cell wall, but plasma membrane more resistant to osmotic pressure
extracellular vesicles (EVs)
small membrane-bound particles
develop when a membrane buds out, pinches off, and is released from the cell
gram positive EV
made of the plasma membrane surrounding a small amount of cytoplasm
gram negative EV
made of LPS containing outer membrane surrounding a sample of periplasm
capsules
well organized layers that are most often composed of polysaccharides and not easily removed from cell
- helps protect from desiccation, resists phagocytosis from hose, exclude viruses and most hydrophobic toxic materials
s-layer
a regularly structured layer composed of protein or glycoprotein that lies on the surface of many bacteria and archaea
- like capsules but are easily removed
- look like floor tiles
- “armored” protection for bacteria
in gram negative adheres to outer membrane
in gram positive associates with peptidoglycan
s-layer functions
- protect from ion and pH fluctuations, osmotic stress, enzymes, and predation
- maintains shape and rigidity
- promotes adhesion to surfaces
- protects from host defences
- potential use in nanotechnology
protoplast
plasma membrane and everything within
cytoplasm
the material bounded by the plasma membrane
cytosol
liquid component of cytoplasm
cytoskeleton
composed of several types of protein filaments
play role in cell division, maintaining cell shape, and positioning and segregating inclusions and plasmid DNA
intracytoplasmic membrane
plasma membrane infoldings
- observed in many photosynthetic bacteria
- observed in many bacteria with high respiratory activity
- may be aggregates of spherical vesicles
inclusions
common in all cells
formed by the aggregation of organic and inorganic substances
primary function - segregate cellular components so they do not diffuse freely in the cytoplasm
function as storage sites, locations to sequester enzymatic reactions or guides for cell movement
can take the form of granules, crystals, globules
gas vacuoles
type of inclusion
involved in bacterial movement
provide buoyancy to aquatic bacteria
made of aggregates of hollow, cylindrical gas vesicles
ribosomes
site of protein synthesis
nucleoid
ellipsoidal region that contains the cell’s chromosome and numerous proteins
usually not membrane bound
plasmids
double stranded dna molecules that can exists independently of the chromosome
- carry genes that can confer a selective advantage in some situations
episomes
plasmids that can integrate into the chromosome
fimbriae
short, think, hairlike protein appendages that can mediate attachment to surfaces, motility
sex pili
longer, thicker, less numerous
genetically encoded on plasmids
required for conjugating
- motility
flagella
threadlike, locomotor appendages extending outward from plasma membrane and cell wall
motility, attachment to surfaces, virulence factors
3 parts of flagella
filament - extends from cell surface to tip
basal body - embedded in cell envelope
hook - short curved segment
chemotaxis
movement towards chemical attractants and away from repellents
two types of flagellar swimming movement
run - moves the cell from one spot to another
tumble - reorients the cell
swarming motility
type of group behavior in which the cells move in unison across a moist surface
spirochete motility
undulation of the entire cell
multiple flagella form axial fibril which winds around the cell
twitching motility
short, intermittent, jerky motions of up to several micrometers in length and is normally seen on moist surfaces
- does not involve flagella
- pili at ends of cell
gliding motility
smooth movements that do not require appendages
slime secretion to reduce friction
endospores
complex, dormant structure formed by some bacteria
form in response to nutrient depletion
resistant to numerous environmental conditions
- heat, UV radiation, gamma radiation, chemical disinfectants, and desiccation
endospore structures
exosporium - thin covering surrounding spore
spore coat - thick layers of protein
cortex - thick peptidoglycan
core - has nucleoid and ribosomes
sporulation
commences when growth slows die to nutrient limitation
a survival mechanism that allows the bacterium to produce a dormant cell that can persist until nutrients are available and vegetative growth can resume
