Chapter 2: Bacterial structures Flashcards
What bacterial structure gives rigid support, protects against osmotic pressure?
peptidoglycan
peptidoglycan - function?
gives rigid support, protects against osmotic pressure
peptidoglycan - chemical composition?
sugar backbone with peptide side chains cross-linked by transpeptidase
what bacterial structure has the chemical composition of a sugar backbone with peptide side chains cross-linked by transpeptidase?
peptidoglycan
cell wall (cell membrane of gram+) - function?
major surface antigen
what bacterial structure is the major surface antigen of gram+ bacteria?
cell wall/cell membrane
cell wall (cell membrane of gram+) - chemical composition?
peptidoglycan for support
lipoteichoic acid induces TNF and IL-1
Which bacterial structure is composed of peptidoglycan and lipoteichoic acid?
cell wall (cell membrane of gram+)
outer membrane (gram-) - function?
major surface antigen
site of endotoxin (LPS)
what bacterial structure is the major surface antigen of gram- bacteria?
outer membrane (containing LPS)
outer membrane (gram-) - chemical composition?
Lipid A induces TNF and IL-1
O polysaccharide is the antigen
what bacterial structure is composed of Lipid A and O polysaccharide?
outer membrane of gram-
plasma membrane - function?
site of oxidative and transport enzymes
what bacterial structure is the site of oxidative and transport enzymes?
plasma membrane
plasma membrane - chemical composition?
phospholipid bilayer
what bacterial structure is composed of a phospholipid bilayer?
plasma membrane
ribosome - function?
protein synthesis
what bacterial structure is the site of protein synthesis?
ribosome
ribosome - chemical composition?
50S and 30S subunits
periplasm - function?
space between the cytoplasmic membrane and outer membrane in gram- bacteria
what bacterial structure is the space between the cytoplasmic membrane and outer membrane of gram- bacteria?
periplasm
periplasm - chemical composition?
contains many hydrolytic enzymes, including \beta-lactamases
which bacterial structure contains many hydrolytic enzymes, including \beta-lactamases?
periplasm
capsule - function?
protects against phagocytosis by macrophages and neutrophils
what bacterial structure protects against phagocytosis by macrophages and neutrophils?
capsule
capsule - chemical composition?
polysaccharide
what bacterial structure is composed of polysaccharide? (2)
capsule
glycocalyx
what is the exception to capsule being composed of polysaccharide?
Bacillus anthracis, which contains D-glutamate amino acids
what is the capsule of Bacillus anthracis composed of?
D-glutamate amino acids
pilus/fimbriae - function?
mediate adherence of bacteria to cell surface;
sex pilus forms attachment between 2 bacteria during conjugation
what bacterial structure mediates adherence of bacteria to cell surface and forms attachment between 2 bacteria during conjugation?
pilus/fimbriae
pilus/fimbriae - composition?
glycoprotein
what bacterial structure is composed of glycoprotein?
pilus/fimbriae
flagellum - function?
motility
what bacterial structure is used for motility?
flagellum
flagellum - chemical composition?
protein
spore - function?
resistant to dehydration, heat, and chemicals
what bacterial structure is resistant to dehydration, heat, and chemicals?
spore
spore - chemical composition? (3)
keratin-like coat
dipicolinic acid
peptidoglycan
what bacterial structure is composed of a keratin-like coat, dipicolinic acid, and peptidoglycan?
spore
plasmid - function?
contains a variety of genes for antibiotic resistance, enzymes, and toxins
what bacterial structure contains a variety of genes for antibiotic resistance, enzymes, and toxins?
plasmid
plasmid - chemical composition?
small circles of double-stranded DNA
glycocalyx - function?
mediates adherence to surfaces, especially foreign surfaces (e.g., indwelling catheters). forms biofilms
what bacterial structure mediates adherence to surfaces, especially foreign surfaces (e.g., indwelling catheters) as biofilms?
glycocalyx
glycocalyx - chemical composition?
polysaccharide
What are the steps to the Gram stain? (4)
1) Pour on crystal violet stain (a blue dye) and wait 60 seconds.
2) Wash off with water and flood with iodine solution. Wait 60 seconds.
3) Wash off with water and then “decolorize” with 95% alcohol.
4) Finally, counter-stain with safranin (a red dye). Wait 30 seconds and wash off with water.
What color do Gram-positive cells appear on Gram stain? Why?
Blue (“I’m positively blue over you”).
Gram+ cells absorb the crystal violet and hold on to it in their thick cross-linked peptidoglycan cell wall.
What cells stain blue on Gram stain?
Gram-positive
What color do Gram-negative cells appear on Gram stain? Why?
Red (“No (negative) red commies”.
The crystal violet is washed off by the alcohol (alcohol partially dissolves the LPS-containing outer cell membrane) and the cells absorb the red safranin in their thin peptidoglycan cell wall.
What cell stain red on Gram stain?
Gram-negative
what is the layer just outside of the bacterial cytoplasmic membrane?
peptidoglycan layer (cell wall)
What kind of cells have a peptidoglycan (cell wall) layer?
All bacterial cells, both Gram+ and Gram-
transpeptidase - function?
catalyzes the formation of peptidoglycan linkages (composed of repeating disaccharides with 4 amino acids in a side chain)
what enzyme catalyzes the formation of peptidoglycan linkages (composed of repeating disaccharides with 4 amino acids in a side chain)?
transpeptidase
penicillin binds to and inhibits what enzyme in bacteria?
transpeptidase
transpeptidase is inhibited by what antibiotic?
penicillin
What is the difference in peptidoglycan cell wall between Gram+ and Gram- bacteria? (2)
1) thickness: Gram+ cell wall is very thick and Gram- cell wall is very thin
2) cross-linking: Gram+ cell wall has extensive cross-linking of the peptidoglycan amino-acid side chains. Gram- cell wall has a fairly simple cross-linking pattern.
What is the composition of the Gram-positive cell envelope?
1) cytoplasmic membrane, with embedded proteins
2) peptidoglycan cell wall, with teichoic acid
What important molecule is present in the peptidoglycan cell wall of Gram-positives?
teichoic acid
teichoic acid is present in the peptidoglycan cell wall of which Gram bacteria?
Gram-positives
What type of bacteria have a thick peptidoglycan cell wall?
Gram-positives
what type of bacteria have a cell wall with more extensive cross-linking of peptidoglycan amino acid side chains?
Gram-positives
What type of bacteria have a thin peptidoglycan cell wall?
Gram-negatives
What type of bacteria have a cell wall with fairly simple cross-linking of peptidoglycan amino acid side chains?
Gram-negatives
What polysaccharide acts as the major antigenic determinant of Gram-positive bacteria?
teichoic acid
what is teichoic acid?
polysaccharide present in the peptidoglycan cell wall of Gram-positive bacteria
What is the composition of the Gram-negative cell envelope?
1) cytoplasmic membrane, with embedded proteins
(periplasmic space)
2) peptidoglycan cell wall (thin), with murein lipoprotein
3) outer cell membrane, with LPS
What important molecule is present in the peptidoglycan cell wall of Gram-negatives?
murein lipoprotein
murein lipoprotein is present in the peptidoglycan cell wall of which type of bacteria?
Gram-negatives
What is murein lipoprotein?
a small helical lipoprotein that originates in the peptioglycan layer of Gram-negative bacteria and extends outward to bind the third outer membrane
What molecule is found in the unique third outer membrane of Gram-negative bacteria?
LPS
Where is LPS found?
In the third outer membrane of Gram-negative bacteria
What components of the cell envelope are unique to Gram-positive bacteria?
lipoteichoic acid
What components of the cell envelope are unique to Gram-negative bacteria? (3)
LPS (endotoxin) (outer membrane)
periplasm
porins
What are the 3 components in the structure of LPS?
1) O-specific side chain
2) Core polysaccharide
3) Lipid A
What is O-antigen/ O-specific side chain?
outer carbohydrate chain of LPS (on the outer membrane of Gram-negatives) that extend into the surrounding media. They differ from one organism to another and are antigenic determinants.
What is lipid A?
aka Gram-negative Endotoxin.
A disaccharide with multiple fatty acid tails reaching into the membrane. interior to the core polysaccharide of LPS on the outer membrane of Gram-negatives.
What is endotoxin and how does it work?
Endotoxin = Lipid A
When Gram-negative bacteria are lysed by uman immune system, fragments of membrane containing Lipid A are released into the circulation, causing fever, diarrhea, and possibly fatal endotoxic (septic) shock.
What are porins and where are they located?
Porins allow passage of nutrients.
Embedded in the gram-negative outer membrane.
Which type of bacteria are vulnerable to antibiotics and chemicals that attack the peptidoglycan cell wall (penicillins and lysozyme)? Why?
Gram-positives are vulnerable.
The Gram-positive thickly-meshed peptidoglycan layer does not block diffusion of low molecular weight compounds, so substances that damage the cytoplasmic membrane (such as antibiotics, dyes, detergents) can pass through.
Which type of bacteria are resistant to antibiotics and chemicals that attack the peptidoglycan cell wall (penicillins and lysozyme)? Why?
Gram-negatives are resistant.
The Gram-negative outer LPS-containing cell membrane blocks the passage of these substances into the peptidoglycan layer and sensitive inner cytoplasmic membrane.
Which 2 tests can be used to visualize capsules under the microscope?
1) India ink stain
2) Quellung reaction
How does the India ink stain allow you to detect bacterial capsules? What microbe does it detect?
India ink stain is not taken up by the capsule, so the capsule appears as a transparent halo around the cell.
This test is used primarily to identify the fungus (yeast) Cryptococcus neoformans
How does the Quellung reaction allow you to detect bacterial capsules?
The bacteria are mixed with antibodies that bind to the capsule. When these antibodies bind, the capsule swells with water.
opsonization - defn
the process of antibodies binding to the capsule, and allow macrophages and neutrophils to bind to (via Fc region) antibody and eat the encapsulated bacteria.
Examples of encapsulated bacteria (8+1)
"Even Some Super Killers Have (Pretty) Nice Big Capsules" or "SHiNE SKiS" 1) E.coli 2) Streptococcus pneumoniae 3) Salmonella 4) Klebsiella pneumoniae 5) Haemophilus influenzae () Pseudomonus aerigonosa 6) Neisseria mengitidis 7) Group B Strep 8) Cryptococcus Neoformans (yeast)
Why are asplenics at risk for severe infection?
Asplenics have decreased opsonizing ability (decreased macrophages and neutrophils) so they cannot easily clear infections
Vaccines for S. pneumoniae, H. influenzae, and N. meningitidis target what structure?
capsule
Capsule + protein conjugate serve as the antigen in vaccines
Vaccines in which the capsule + a protein conjugate serve as the antigen are available for which microbes? (3)
1) S. pneumoniae: PCV (Prevnar), PPSV (Pneumovax, no conjugated protein)
2) H. influenzae type B
3) N. meningitidis
Which bacteria form endospores? What is their Gram stain and morphology?
Bacillus and Clostridium. Both are Gram-positive rods.
Bacillus and Clostridium form what specialized structure?
endospores
Endospores are resistant to what? (4)
heat (boiling)
cold
drying
chemical agents)
What are the layers of the endospore protective coat? (5)
1) cell membrane
2) thick peptidoglycan mesh
3) another cell membrane
4) wall of keratin-like protein
5) outer layer called the exosporium
When do spores form?
when there is a shortage of needed nutrients, and can lie dormant for years
Which bugs are urease-positive? (8)
“CHuck Norris hates PUNKSS”
1) Cryptococcus
2) H. pylori
3) Proteus
4) Ureaplasma
5) Nocardia
