Chapter 3 Flashcards
6 different shapes of bacteria and archaea (depends on the cell membrane)
coccus, rod, spirillum,spirochete,budding and appendaged bacteria, filamentous bacteria
the cell wall of bacteria allows what
to withstand the intracellular osmotic pressure
the cell wall is responsible for what (2)
shape and rigidity of the bacteria
4 steps of Gram’s Stain + the result of each step
- flood the head-fixed smear with crystal violet for 1
min (result: all cells purple) - add iodine solution for 1 min (result: all cells purple)
- decolorize with alcohol briefly (20 sec) (result: gram-positive (G+) cells are purple and gram-negative cells (G-) are colorless
- counterstain with safranin for 1-2 min (result: G+ are purple, G- are pink to red)
why the dye is not washed away in G+ but it is in G-
layer of peptidoglican is thickier in G+
what is peptidoglican and it subunits (3)
it is a polymer (murein)
subunits:
- 2 sugars: NAM (N-acetulmuramic) and NAG
- short peptide side chain containing unusual amino acids: D-amino acids instead of L-amino acids found in proteins
- NAM and DAP (diaminopimelic acid) have never been found in Eukarya or Archaea
** polymerization of the sugar backbone: NAG-NAM-NAG-NAM…
what is the target of the lysozymes, how it is secreted (3)
its target is the link between NAG and NAM
- its secreted in tears, saliva and other body fluids to protect against bacterial pathogens
what provides rigidity in the peptidoglycan of Bacteria
- the polymerisation of the sugar backbone provides rigidity to the structure in only one direction
- another bond between the peptides of two adjacent peptidoglycan chain provides rigidity in the other direction
type of cross-linking for positive and negative gram
positive gram: interbridge cross-linking
negative gram: direct cross-linking
how do we call cross-linking
transpeptidation
composition of cell wall Gram positive (3)
- 90% is made of peptidoglycan
- Teichoic acid and lipoteichoic acid that are composed of glycerol-P (3C) or ribitol-P (5C), and decorated with amino acids and sugars ** they are covalently bounded to peptidoglycan
- wall-associated protein are attached covalently to the pepdtidoglycan by an enzyme called sortase
4 compositions of the cell wall of the Gram negative
- 5-10% of peptidoglycan
- surface proteins are anchored in the outer membrane (contain hydrophobic domain)
- the periplasm (also called protein gel because it is very dense) contains a high concentrations of proteins
- the outer membrane sometimes called LPS layer
proteins in the periplasm of the cell wall of the Gram negative are involved in what (3)
- nutrient acquisition
- extracellular enzymatic reactions
- sensing
…
what is the role of the LPS layer (in the cell wall of the Gram negative)
helps protect the bacteria against a variety of substances, including antibiotics, and against the host defense system
what is LPS
a family of complex sugar polymers attached to a lipid moiety known as lipid A
characteristics of lipid A (what is it, role, risks)
- it’s an endotoxin
- it plays a role in the pathogenesis of Gram-negative bacterial pathogens
- it is toxic to many animals, it can cause acute inflammation and vascular problems (septic shock) that can result in death
composition of lipid A
- contains 6 lipids tails that are embedded in the membrane
- KDO: 2-keto-deoxyoctonate, links the lipid A to the polysaccharide chain
- GLcN: N-acetylglucosamine (as in peptidoglycan)
what is O-specific polysaccharide + what it can be used for
- also known as O antigen
- consists of repeating sequences of 2-4 monosaccharides
- there is a huge diversity of O antigen so it can be used to identify different strains of one species of bacteria
characteristics of cell walls of Archaea (4)
- peptidoglycan is absent and usually no outer membrane
- may consists of proteins (usually), polysaccharides and/or glycoproteins
- linkage between sugars are insensible to lysozyme, unlike peptidoglycan
- pseudomurein
difference between the structure of pseudomurein and pseudopeptidoglycan
their structures are similar but pseudomurein contains N-acetyltalosaminuronic acid instead of NAM and lack D-amino acids
what is the composition of the great majority of the cell walls of Archaea
proteins and/or glycoproteins
what is particular with the cell wall that are majority composed of proteins and glycoproteins called paracrystalline surface layer or S-layers
these cell walls have a crystalline appareance when viewed by electron microscopy
what type of cell walls from the Archaea family is also present in some bacteria species
S-layer
It forms an additional layer on top of the peptidoglycan (gram-positive) or on top of the outer membrane (Gram-negative)
what is the capsule or slime layers
it is a layer that bacteria and archaea species may synthesize
what is the capsule or slime layers composed of and where is it bound
polysaccharide (vast majority) or proteins
- heteropolysaccharides (majority of bacteria)
- homoploysaccharides (some Gram-negative)
- may be covalently bound to the outer membrane or to the peptidoglycan layer
why is the capsule or slime layer important
it is a very important virulence determinant for capsulated bacterial pathogens- the capsule protects against the host defense system
2 surface appendages of bacteria
flagella and fimbriae
role of flagella + size
they are used for locomotion
15-20 um long
what are monotrichous, peritrichous and lophotrichous
- one flagellum
- many flagella, all around the cell surface
- many flagella, originating from one end of the cells, polar flagellation
where is the bacterial flagellum
it is anchored in the cytplasmic membrane **BUT NOT COVER BY THE CYTOPLASMIC MEMBRANE.MUCH MUCH smaller than the eukaryotes flagella/cilia
how many genes are involved in motility (biosynthesis of flagella, structure or regulation)
50
where is the growth of the filament take place
at the tip
what do the cap during the flagellum biosynthesis
assists flagellins to organize at the Tip
how many subunit/flagella
20 000 flagellin subunit
another way than flagella to move around
gliding motility
what is taxis
directed movement toward or away from a gradient of chemical or physical agents
4 types of taxis
- chemotaxis: chemicals, nutrients, antibiotics
- phototaxis: light (phototrophic organisms)
- aerotaxis: oxygen
- osmotaxis: ionic strenght (high/low salt concentration)
role of fimbriae, its structure, its size and where do we find them
- involve primarily in the attachment of the microorganisms to surface
- form rigid, rod-like structure
- usually less than 4um long
- found primarily in Gram-genative bacteria
P fimbriae is produced by what
uropathogenic E. coli
proteins required for the assembly of the fimbriae of Gram-negative bacteria
chaperone and usher (chaperone-usher system)
in contrast of flagella, fambria of Gram-negative bacteria grow from …
the base
how subunits of fimbriae of Gram-negative bacteria are assembled
by strand exchange (like puzzle pieces)
how adhesion of fimbriae of Gram-negative bacteria can be mediated by (2)
- the main subunits
- a specialized subunit at the tip (as is the case with the P fimbriae)
in Gram-positives, how is the adhesion to surfaces is made
- it is generally carried out by surface adhesin, consisting of one protein
- such adhesins mediate very close attachment
fimbriae of Gram-positives are assembled by ____ and attached to the ______
sortases
peptidoglycan
3 differences between the fimbriae of Gram-negative and Gram-positive bacteria
- Fimbrie of Gram-positive are anchored in the peptidoglycan and the one sof Gram-negatives are anchored in the outer membrane
- Gram-positive are covalently- linked to one another and Gram-negative are not covalently bound to one another (strand exchange)
- Gram-positive are assembled enzymatically by sortases and Gram-negative need accessory proteins, encoded with the fimbria pilin genes
what is an endospore
- they are highly differenciated cells that are extremely resistant to harsh environmental conditions: desiccation, heat, chemicals, radiations, nutrients depletion
- is is a dormance stage in the lifecycle and it is easily dispersed by water, wind, animal digestive system..
- can remain dormant for 100s of years
in which species spores are best studied (2)
Clostridium species Bacillus species (gram-positive)
composition of the endospores + what they contain (5)
- exosporium: proteins
- spore coat: layers of spore-specific proteins (keratins like)
- cortex: peptidoglycan
- Core (cytoplasm): Ca2+, dipicolinic aci (DPA), SASPs (small, acid soluble spore proteins), also conatin protein needed for germination
- DNA
what is unique to spore that you will not find in bacteria
DPA (dipicolinic acid)
what do SASPs (small, acid soluble spore proteins)
it binds to DNA and help protect it against damage (UV light)
what do DPA and Ca2+
bind water, dehydrate the core
step for the formation of the endospore
- asymmetric cell division: commitment to sporulation
- engulfment
- cortex formation
- spore coat, Ca2+ uptake, SASPs, dipicolinic acid
- maturation, cell lysis
- germination
what is need for the germination to occurs
heat (70 degree) and water
what is germination
the mechanism that converts the spore from a dormant biological organism to one that grows vegetatively and is capable of either sexual or asexual reproduction
3 types of nutrients that are storage in cell inlucsions
carbon
sulfur
polyphosphate
in some cases, cell inclusions can be enclosed by what
a single layer membrane (phospholipid, protein, glycoprotein)
some cell inclusions confers __
buoyancy (to decrease density, have more floatation)
what contains magnetosomes and what allows the bacteria
magnetites, allow them to respond to magnetic field (magnetotaxis) : help them to know the up and down, to know which direction they should swim to go away from oxygen
2 roles of the enzyme sortase
- in gram-positive bacteria, wall-associated protein are covalently attached to peptidoglycan by sortase
- fimbriae of Gram-positive bacteria are assembled by sortases and attached to peptidoglycan
2 mechanisms of gliding motility
- secretion of mucus
2. type 4 pilus-dependant
