Exam 1 - Lecture 3 Flashcards
what are the three types of peptidoglycan variations?
- composition of linkage (direct or bridges)
- amino acid at #3 position
- linkage type (2 to 4, 3 to 4)
which type of amino acid is usually only found in bacterial cell walls, L- or D-?
D- amino acids
what kind of linkage connects NAM and NAG sugars?
beta-(1,4) glycosidic bonds
how thick is the peptidoglycan layer in Gram-positive cell walls?
20-80 nm thick
what are teichoic acids?
are they found in Gram-positive or Gram negative cell walls?
- negatively charged acids that help maintain the cell envelope, protect from environmental substances, and may bind to host cells
- only found in Gram-positive walls
what are teichoic acids composed of?
alternating phosphate and glycerol groups
where can you find teichoic acids? what about lipoteichoic acids?
teichoic: covalently attached to peptidoglycan
lipoteichoic: covalently attached to lipids in plasma membrane
what is the cell wall protein sequence in Gram-positive cell walls?
which residue of the sequence is covalently linked to peptidoglycan via what enzyme?
- LPXTG
- T residue, Sortase
what is an LPS?
lipopolysaccharide
how many membranes does a Gram-negative cell wall have?
what are they called?
- two
- outer membrane and inner/plasma membrane
do Gram-negative cells have teichoic acids?
nope
what connects the outer membrane to the peptidoglycan in Gram-negative bacteria?
Braun’s lipoprotein
what is the inner leaflet of the outer membrane composed of in Gram-negative bacteria?
phospholipids
what is the outer leaflet of the outer membrane composed of in Gram-negative bacteria?
lipopolysaccharide (LPS)
where is LPS found?
only in Gram-negative bacteria
what are the three parts of LPS?
- O antigen
- core polysaccharide
- Lipid A
what parts of LPS are embedded in the outer membrane, and which extend out from the cell?
Lipid A is embedded in the outer membrane
O antigens and the core polysaccharide extend from the cell
what is the importance of LPS?
- contributes to negative charge on cell surface (core polysaccharide)
- stabilizes the outer membrane (Lipid A)
- protects from host defenses (O antigen)
- creates permeability barrier
- can act as a toxin (lipid A)
how many endotoxins do we have?
one! (LPS’s Lipid A)
what makes the outer membrane permeable?
the presence of porin proteins: channels that let small molecules pass through
what is the mechanism of Gram-staining in Gram-positive cells?
the constriction/shrinkage of the thick peptidoglycan layer prevents loss of crystal violet during decolorization
why doesn’t the peptidoglycan layer in Gram-negative cells retain crystal violet?
the peptidoglycan layer is thinner and more porous
can you explain the steps of Gram-staining?
- crystal violet dye is added
- iodine is added
- complex forms between CV and iodine
- the sample is decolorized (with ethanol)
- the thinner Gram-negative cells lose their color, Gram-positive stays purple
- a counterstain, safranin, is added
- Gram-positive cells are now pink
what protects bacterial cells from osmotic stress?
the cell wall
what is a hypotonic environment?
- the solute concentration is higher inside the cell
- water moves into the cell and cell swells
- cell wall protects from lysis
what is a hypertonic environment?
- the solute concentration is higher outside the cell
- water leaves the cell
- plasmolysis occurs (shrinking of the cytoplasm)
what do we call Gram-positive bacteria without the peptidoglycan?
protoplasts
what do we call Gram-negative bacteria without the peptidoglycan?
spheroplasts
if the peptidoglycan cell wall is removed, the cells will lyse in _____tonic solution and survive in _____tonic solution
hypotonic; isotonic
what are the three most common types of external layers found in bacteria?
- capsules
- slime layers
- S-layers
what is the role of the external layer in bacteria?
plays a role in interaction of the bacterial cell and its environment
what are capsules composed of?
polysaccharides (sugars)
true of false: capsules are well organized and not easily removed from the cell.
true
what are the protective advantages of capsules?
- resistant to phagocytosis
- protect from desiccation
- exclude viruses and detergents
true of false: slime layers are well organized and not easily removed from the cell.
false; slime layers diffuse, are unorganized, and are removed easily
what might slime layers aid in?
motility
what are S-layers?
regularly structured layers of protein or glycoproteins that self-assemble
where does the S-layer adhere to in Gram-negative bacteria?
Gram-positive bacteria?
- the outer membrane
- the peptidoglycan surface
what is the cytoplasm?
material bound by the plasmid membrane
what are the five bacterial cytoplasmic structures?
- cytoskeleton
- intracytoplasmic structures
- ribosomes
- nucleiod and plasmids
- inclusions
what are the three eukaryotic cytoskeletal elements?
- actin
- tubulin
- intermediate filaments
(homologues of all three have been found in bacteria)
what is FstZ? where is it found?
- a tubulin homologue that aids in septum formation during cell division
- found in many bacteria
what is MreB? where is it found?
- an actin homologue that maintains shapes by positioning peptidoglycan synthesis machinery
- found in rods
what is CreS and where is it found?
a rare intermediate filament homologue that maintains the shape of curve shaped bacteria
what does the S in 16S, 80S, etc., stand for?
Svedberg unit
what are ribosomes?
sites for protein synthesis
how big is the eukaryotic ribosome?
prokaryotic (archaeal and bacterial)?
- 80S
- 70S
what ribosomal RNA is found in bacteria (large and small subunits)?
- small subunit: 16S
- large subunit: 23S and 5S
what is in the nucleoid of a cell?
the genetic material
what are plasmids?
extrachromosomal DNA (like extra DNA)
what does it mean when a cell is “cured”?
it has “lost” its plasmids
true or false: plasmids exist and replicate independently of the chromosome and can be inherited during cell division?
true
true of false: there can only be one copy of plasmid in a cell
false; there can be multiple
plasmid genes are (essential or non-essential)?
non-essential
what are inclusions? what is another name for them?
- granules of organic or inorganic material stockpiled by the cell for future use
- sometimes called microcompartments
what are the three best known examples of external structures in bacteria?
pili, fimbriae, and flagella
what are the four functions of external structures in bacteria?
- attachment to surfaces
- cell movement
- protection
- horizontal gene transfer
what is conjugation in bacteria?
transfer of plasmid from one cell to another
what is the main function of flagella?
motility
what does it mean when a bacteria is monotrichous?
it has one flagella
what does it mean when a bacteria is amphitrichous?
it has one flagella at each end
what does it mean when a bacteria is lophotrichous?
it has a cluster of flagella at one or both ends
what does it mean when a bacteria is peritrichous?
it has flagella spread over the entire surface of the cell
what are the three parts of flagella?
- filament
- hook
- basal body
filament subunits self-assemble with the help of filament caps at the (tip or base).
tip, NOT base
what is chemotaxis?
moving towards chemical attractants such as nutrients, and away from harmful substances
what are the four common types of motility?
- flagellar movement
- spirochete motility
- twitching motility
- gliding motility
match the following flagellar movements:
a.) clockwise
b.) counterclockwise
1.) run (forward motion)
2.) tumble (turning)
b1.) counterclockwise is run
a2.) clockwise is tumbling
in spirochetes, where do the flagella remain?
the periplasmic space inside the outer membrane
which describes short, intermittent, jerky motions:
gliding or twitching?
twitching
in the presence of a chemical attractant, does CW rotation of flagella increase or decrease? why?
CW (tumbling) decreases so that the run (CCW) in the direction of the attractant is longer
when concentration of a chemical attractant decreases, does CW rotation of flagella increase or decrease? why?
CW (tumbling) increases so that the cell can redirect until it is moving toward the attractant again
what is sporulation? what is its purpose?
- endospore formation by bacteria
- survival and preservation of the genetic material (NOT reproduction)
what are the three steps of formation of vegetative cells?
- activation (of spores)
- germination
- outgrowth
