Ch 2: Microbial Cell Structures (Bio 286 - Microbiology) Flashcards
optics and properties of light
visible light has wavelengths 400-750 nm; maximum resolution is 1 wavelength; magnification spreads light rays out to 150 micrometers (the resolution of our eyes = distance between photoreceptor cells)
refraction
passage through lens material bends light; parabolic lens brings ray to a focus point; lens with 2 differently shaped convex sides magnifies image
resolution
ability to distinguish two adjacent objects or points from one another; aka resolving power; improved by shorter wavelengths
resolving power (RP) (aka resolution)
calculated as : wavelength of light in nm / 2 x numerical aperture (where the numerical aperture describes the relative efficiency of a lens in bending light rays, numerical aperture is increased with oil immersion lenses)
spirochete
spiral shaped bacteria
spirillum
a more rigid/thicker spiral shaped bacteria
vibrio
curved rod, comma shaped bacteria
bacillus
Rod shaped bacteria
streptobacilli
rod-shaped bacteria occurring in chains
coccus
A spherical bacterium
diplococci
Spherical bacteria that occur in pairs
streptococci
spherical shaped bacteria occurring in chains
tetrad
spherical bacteria occurring in groups of 4
sarcina
spherical bacteria occurring in cubical amounts
staphylococci
Spherical shaped bacteria that form grape-like clusters
advantages to being small microbes
MORE SURFACE AREA RELATIVE TO CELL VOLUME (higher surface area/volume ratio); support greater nutrient and waste product exchange per unit cell volume; tend to GROW FASTER; mutations lead to faster evolutions
cell membrane
structure defining existence of cell
membrane constituents
approximately equal parts of phospholipids and proteins; have hydrophilic and hydrophobic regions that lock the protein in the membrane
phospholipid
consists of glycerol with ester links to two fatty acids and a phosphoryl head group
membrane proteins serve numerous functions
structural support; secretion of virulence factors; transmission of communication signals; ion transport and energy storage
transport across cell membrane
cell membrane acts as a SEMI PERMEABLE BARRIER because SELECTIVE TRANSPORT IS ESSENTIAL FOR SURVIVAL (diffusion and osmosis)
diffusion
easy permeation of the membrane by small uncharged molecules such as O2 and CO2
osmosis
diffusion of water across the membrane
diffusion of weak acids and weak bases
in their uncharged form they can diffuse across the membrane to change the pH of the cell (once diffused across the membrane into the cell, the acid/base will deprotonate/protonate to become charged, changing the pH)
transporters
a specific protein that facilitates transport of polar molecules and charged molecules
passive transport
molecules move along their concentration gradient
active transport
molecules move against their concentration gradient; requires energy
membrane lipids
phospholipids vary with respect to their phosphoryl head groups and their fatty acid side chains; variability is due to changes in temperature, where at high temperatures unsaturated fats (double bonds) dominate and at low temperatures saturated fats (no double bonds) dominate
membrane fluidity
membranes include planar molecules called reinforcing agents that fill gaps between hydrocarbon chains
sterols (cholesterol, egosterol)
reinforcing agents of the membrane in eukaryotes that regulate membrane fluidity
hopanoids / hopanes
reinforcing agents of the membrane in bacteria that regulate membrane fluidity
nucleoid
contains genetic material, NO NUCLEAR MEMBRANE, single circular chromosome, 500000-10000000 nt; HAPLOID; plasmids may be present; DNA is in close proximity to cytoplasm and ribosomes
prokaryote ribosome
two subunits (30S and 50S) that combine for a total size of 70S; dozens of proteins and three rRNA molecules; translates mRNA into proteins
thylakoids
extensively folded intracellular membranes
carboxysomes
polyhedral bodies packed with enzyme Rubisco for CO2 fixation
gas vesicles
to increase buoyancy
phototroph structures
thylakoids, carboxysomes, gas vesicles
other inclusion bodies
storage granules; glycogen, PHB and PHA for energy; sulfur for oxidation; volutin, phosphate; magnetosomes; membrane-embedded crystals of Fe3O4 fixation; orient the swimming of magnetotactic bacteria
bacterial cytoskeleton
shape is determined by its shape-determining proteins: FtsZ, MreB, CreS
FtsZ
forms a “Z-ring” for septum placement
MreB
forms a coil inside rod-shaped cells
Cres (“Crescentin”)
forms a polymer along inner side of crescent-shaped bacteria
cell wall
confers shape and rigidity to cell and helps it withstand turgor pressure (influx of water)
sacculus
bacterial cell wall that consists of a single interlinked molecule (peptidoglycan)
peptidoglycan structure
long polymers N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), bound to a peptide of 4-6 amino acids; where the peptides can form cross-bridges connecting the parallel glycan strands
gram positive bacteria
thick cell wall; one membrane
gram negative bacteria
thin cell wall; two membranes
gram positive cell
polymers of sugars: ribitol-P and glycerol-P; other adducts: D-alanine and sugars; Lipoteichoic acid linked to lipids and act to anchor wall to membrane
mycobacterial (Mycobacterium tuberculosis and M. leprae) cell envelopes
very complex, including unusual membrane lipids (mycolic acid) and unusual sugars (arabinogalactans)
mycolic acids
lipid with a structure of RCH(OH)CH(R)COOH [where R is two long chains]
R groups of different mycolic acids
corynebacterium (30-40 carbons — not too hydrophobic); nocardia (40-60 carbons — somewhat hydrophobic); mycobacterium (60-90 carbons — very hydrophobic)
gram negative outer membrane
thin peptidoglycan layer consisting of one to two sheets; covered by an outer membrane that confers defensive abilities and toxigenic properties on many pathogens
lipopolysaccharide
Lipid A (six fatty acids) for conserved structure; core (adaptor structures) for variable composition; O-Antigen (repeats) for important barrier functions
flagellum structure
bacterial locomotion; electric motor; dozens of proteins; rotates rapidly; many are reversible; propels cell through environment
monotrichous
single flagellum
amphitrichous
flagella at both poles of the cell
lophotrichous
cluster of flagella at one end
peritrichous
flagella distributed over the entire cell
flagella of spirochetes
AXIAL FILAMENTS; flagella located in the periplasm; bundles of many flagella; cause bacterium to corkscrew but can move through viscous media
chemotaxis
movement of bacterium in response to chemical gradients (where attractants cause counterclockwise rotation and flagella to bundle together, and repellents cause clockwise rotation and flagellar bundles to fall apart)
biased random walk
causes a net movement of bacteria toward attractants or away from repellents; movement toward attractant is favored so off-track movements will be redirected
cell attachment methods
fimbriae, stalks, sex pilus
fimbriae
attach cells to surfaces; constructed from thin filaments of protein “fimbrin”
stalks
attach cells to surfaces; secretion systems attach cells to prey; six types
sex pilus
similar to type 4 secretion system, but essential for bacterial pathogenicity
capsule or glycocalyx
outermost layer of the cell; polymeric structures; most are CARBOHYDRATES but a few are peptides; variable in thickness; used to avoid phagocytosis; usually important for pathogenesis
water
greatest volume of a cell (about 70%)
protein
most abundant macromolecule of cells (about 16%) (followed by RNA, about 6%)
fatty acid
hydrophobic
phosphoryl head
hydrophilic
lipoteichoic acid
linked to lipids in cytoplasmic membrane that anchors the cell wall to the membrane; only in gram positive cells
lipopolysaccharide (LPS)
Molecule that makes up the outer layer of the outer membrane of Gram-negative bacteria; only in gram negative cells
core (adaptor structures) of LPS
unique to genus
mycoplasma
true bacteria; very small in size; no peptidoglycan wall [but has a single membrane so is considered a gram positive grouping]; variable in shape; important pathogens; contain cholesterol in membranes but don’t make it themselves; does NOT contain murein
capsule
extracellular slime to make bacteria slippery to avoid phagocytes
small microbes have a higher surface-to-volume ratio
which allows for higher nutrient exchange
ESTER links
lipids in cytoplasmic membrane of bacteria and eukarya
ETHER links
lipids in cytoplasmic membrane of Archaea
hydrolytic enzymes
function in initial degradation of nutrients
lysozyme
enzyme that cleaves bond between NAG and NAM to destroy peptidoglycan and cause bacterial cell lysis as a part of animals’ immune defense
peptide cross bridges
only in Gram positive
archaella of archaeans
rotate like bacterial flagella though they consist of multiple protein types
endospores
contain small acid-soluble proteins (SASPs) which protect DNA from Ultraviolet light
