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Microbiology > Chapter 3 > Flashcards

Chapter 3 Flashcards

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Biology 101 flashcards
1
Q

6 different shapes of bacteria and archaea (depends on the cell membrane)

A

coccus, rod, spirillum,spirochete,budding and appendaged bacteria, filamentous bacteria

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2
Q

the cell wall of bacteria allows what

A

to withstand the intracellular osmotic pressure

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3
Q

the cell wall is responsible for what (2)

A

shape and rigidity of the bacteria

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4
Q

4 steps of Gram’s Stain + the result of each step

A
  1. flood the head-fixed smear with crystal violet for 1
    min (result: all cells purple)
  2. add iodine solution for 1 min (result: all cells purple)
  3. decolorize with alcohol briefly (20 sec) (result: gram-positive (G+) cells are purple and gram-negative cells (G-) are colorless
  4. counterstain with safranin for 1-2 min (result: G+ are purple, G- are pink to red)
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5
Q

why the dye is not washed away in G+ but it is in G-

A

layer of peptidoglican is thickier in G+

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6
Q

what is peptidoglican and it subunits (3)

A

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…

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7
Q

what is the target of the lysozymes, how it is secreted (3)

A

its target is the link between NAG and NAM

- its secreted in tears, saliva and other body fluids to protect against bacterial pathogens

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8
Q

what provides rigidity in the peptidoglycan of Bacteria

A
  • 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
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9
Q

type of cross-linking for positive and negative gram

A

positive gram: interbridge cross-linking

negative gram: direct cross-linking

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10
Q

how do we call cross-linking

A

transpeptidation

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11
Q

composition of cell wall Gram positive (3)

A
  • 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
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12
Q

4 compositions of the cell wall of the Gram negative

A
  1. 5-10% of peptidoglycan
  2. surface proteins are anchored in the outer membrane (contain hydrophobic domain)
  3. the periplasm (also called protein gel because it is very dense) contains a high concentrations of proteins
  4. the outer membrane sometimes called LPS layer
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13
Q

proteins in the periplasm of the cell wall of the Gram negative are involved in what (3)

A
  • nutrient acquisition
  • extracellular enzymatic reactions
  • sensing
    …
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14
Q

what is the role of the LPS layer (in the cell wall of the Gram negative)

A

helps protect the bacteria against a variety of substances, including antibiotics, and against the host defense system

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15
Q

what is LPS

A

a family of complex sugar polymers attached to a lipid moiety known as lipid A

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16
Q

characteristics of lipid A (what is it, role, risks)

A
  • 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
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17
Q

composition of lipid A

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)
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18
Q

what is O-specific polysaccharide + what it can be used for

A
  • 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
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19
Q

characteristics of cell walls of Archaea (4)

A
  • 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
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20
Q

difference between the structure of pseudomurein and pseudopeptidoglycan

A

their structures are similar but pseudomurein contains N-acetyltalosaminuronic acid instead of NAM and lack D-amino acids

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21
Q

what is the composition of the great majority of the cell walls of Archaea

A

proteins and/or glycoproteins

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22
Q

what is particular with the cell wall that are majority composed of proteins and glycoproteins called paracrystalline surface layer or S-layers

A

these cell walls have a crystalline appareance when viewed by electron microscopy

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23
Q

what type of cell walls from the Archaea family is also present in some bacteria species

A

S-layer

It forms an additional layer on top of the peptidoglycan (gram-positive) or on top of the outer membrane (Gram-negative)

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24
Q

what is the capsule or slime layers

A

it is a layer that bacteria and archaea species may synthesize

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25
Q

what is the capsule or slime layers composed of and where is it bound

A

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
26
Q

why is the capsule or slime layer important

A

it is a very important virulence determinant for capsulated bacterial pathogens- the capsule protects against the host defense system

27
Q

2 surface appendages of bacteria

A

flagella and fimbriae

28
Q

role of flagella + size

A

they are used for locomotion

15-20 um long

29
Q

what are monotrichous, peritrichous and lophotrichous

A
  1. one flagellum
  2. many flagella, all around the cell surface
  3. many flagella, originating from one end of the cells, polar flagellation
30
Q

where is the bacterial flagellum

A

it is anchored in the cytplasmic membrane **BUT NOT COVER BY THE CYTOPLASMIC MEMBRANE.MUCH MUCH smaller than the eukaryotes flagella/cilia

31
Q

how many genes are involved in motility (biosynthesis of flagella, structure or regulation)

A

50

32
Q

where is the growth of the filament take place

A

at the tip

33
Q

what do the cap during the flagellum biosynthesis

A

assists flagellins to organize at the Tip

34
Q

how many subunit/flagella

A

20 000 flagellin subunit

35
Q

another way than flagella to move around

A

gliding motility

36
Q

what is taxis

A

directed movement toward or away from a gradient of chemical or physical agents

37
Q

4 types of taxis

A
  1. chemotaxis: chemicals, nutrients, antibiotics
  2. phototaxis: light (phototrophic organisms)
  3. aerotaxis: oxygen
  4. osmotaxis: ionic strenght (high/low salt concentration)
38
Q

role of fimbriae, its structure, its size and where do we find them

A
  • 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
39
Q

P fimbriae is produced by what

A

uropathogenic E. coli

40
Q

proteins required for the assembly of the fimbriae of Gram-negative bacteria

A

chaperone and usher (chaperone-usher system)

41
Q

in contrast of flagella, fambria of Gram-negative bacteria grow from …

A

the base

42
Q

how subunits of fimbriae of Gram-negative bacteria are assembled

A

by strand exchange (like puzzle pieces)

43
Q

how adhesion of fimbriae of Gram-negative bacteria can be mediated by (2)

A
  • the main subunits

- a specialized subunit at the tip (as is the case with the P fimbriae)

44
Q

in Gram-positives, how is the adhesion to surfaces is made

A
  • it is generally carried out by surface adhesin, consisting of one protein
  • such adhesins mediate very close attachment
45
Q

fimbriae of Gram-positives are assembled by ____ and attached to the ______

A

sortases

peptidoglycan

46
Q

3 differences between the fimbriae of Gram-negative and Gram-positive bacteria

A
  1. Fimbrie of Gram-positive are anchored in the peptidoglycan and the one sof Gram-negatives are anchored in the outer membrane
  2. Gram-positive are covalently- linked to one another and Gram-negative are not covalently bound to one another (strand exchange)
  3. Gram-positive are assembled enzymatically by sortases and Gram-negative need accessory proteins, encoded with the fimbria pilin genes
47
Q

what is an endospore

A
  • 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
48
Q

in which species spores are best studied (2)

A 
Clostridium species
Bacillus species (gram-positive)
49
Q

composition of the endospores + what they contain (5)

A
  1. exosporium: proteins
  2. spore coat: layers of spore-specific proteins (keratins like)
  3. cortex: peptidoglycan
  4. Core (cytoplasm): Ca2+, dipicolinic aci (DPA), SASPs (small, acid soluble spore proteins), also conatin protein needed for germination
  5. DNA
50
Q

what is unique to spore that you will not find in bacteria

A

DPA (dipicolinic acid)

51
Q

what do SASPs (small, acid soluble spore proteins)

A

it binds to DNA and help protect it against damage (UV light)

52
Q

what do DPA and Ca2+

A

bind water, dehydrate the core

53
Q

step for the formation of the endospore

A
  1. asymmetric cell division: commitment to sporulation
  2. engulfment
  3. cortex formation
  4. spore coat, Ca2+ uptake, SASPs, dipicolinic acid
  5. maturation, cell lysis
  6. germination
54
Q

what is need for the germination to occurs

A

heat (70 degree) and water

55
Q

what is germination

A

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

56
Q

3 types of nutrients that are storage in cell inlucsions

A

carbon
sulfur
polyphosphate

57
Q

in some cases, cell inclusions can be enclosed by what

A

a single layer membrane (phospholipid, protein, glycoprotein)

58
Q

some cell inclusions confers __

A

buoyancy (to decrease density, have more floatation)

59
Q

what contains magnetosomes and what allows the bacteria

A

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

60
Q

2 roles of the enzyme sortase

A
  1. in gram-positive bacteria, wall-associated protein are covalently attached to peptidoglycan by sortase
  2. fimbriae of Gram-positive bacteria are assembled by sortases and attached to peptidoglycan
61
Q

2 mechanisms of gliding motility

A
  1. secretion of mucus

2. type 4 pilus-dependant

Microbiology (25 decks)

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