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Microbiology & Immunology > Fundamentals in Microbiology > Flashcards

Fundamentals in Microbiology Flashcards

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1
Q

What is the difference between bacterial (prokaryotic) DNA and eukaryotic DNA?

A

Bacterial DNA is circular whereas eukaryotic DNA is in chromosomes and is linear with telomeres

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2
Q

What do eukaryotes have that bacteria (prokaryotes) lack?

A

Histones

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3
Q

What is an operon?

A

A cluster of many genes encoding enzymes of a single biochemical pathway

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4
Q

What kind of genes do bacterial chromosomes contain?

A

Housekeeping genes

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5
Q

What are housekeeping genes?

A

Genes that are essential for the maintenance of cells - e.g. for transport and replication

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6
Q

Where are housekeeping genes located?

A

On the chromosome

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7
Q

What are pathogenicity islands?

A

Distinct genetic elements on the chromosomes of a large number of bacterial pathogens

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8
Q

What do pathogenicity islands encode?

A

Various virulence factors and are normally absent from non-pathogenic strains of the same or closely-related species

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9
Q

What are secretion systems and what do they have a role in?

A

They are transport systems in bacteria that have a role in pathogenesis

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10
Q

What are some bacteria that have pathogenicity islands?

A

Salmonella, shigella, enteropathogenic E. coli, staphylococcus aureus

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11
Q

What do DNA polymerases do?

A

Catalyse the addition of nucleotides

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12
Q

Which organisms are plasmids found in?

A

Prokaryotes

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13
Q

Do plasmids replicate independently of the host chromosome?

A

Yes, they possess their own origin of replication so can replicate independently

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14
Q

Name an example of a function of a plasmid

A

Antibiotic resistance

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15
Q

What type of antibiotic is penicillinase?

A

A beta-lactamase

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16
Q

What do beta-lactamases do?

A

They split the beta-lactam ring inactivating the antibiotic penicillin

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17
Q

What are the 4 main mechanisms bacteria use to acquire new traits?

A
  1. Genetic rearrangement (point mutations, insertion, deletions, etc.)
  2. Natural transformation (uptake and incorporation of naked DNA)
  3. Conjugation (genetic exchange between bacteria)
  4. Transduction (exchange occurs as consequence of phage predation)
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18
Q

What role does the bacterial cell wall/envelope play?

A

Provides bacteria with their shape, rigidity and structure and is involved in the transport of materials in and out of the cell

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19
Q

What is the difference between gram positive and gram negative bacteria?

A

Gram-negative bacteria have an outer membrane that gram-positive do not

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20
Q

Is the peptidoglycan layer thicker in Gram-positive or Gram-negative bacteria?

A

Gram-positive

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21
Q

What colour are Gram-positive bacteria when stained?

A

Purple

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22
Q

What colour are Gram-negative bacteria when stained?

A

Pink

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23
Q

Are teichoic and lipoteichoic acids present on Gram-negative or Gram-positive bacteria?

A

Gram-positive

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24
Q

Do Gram-positive bacteria look smooth or ruffled under a microscope?

A

Smooth

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25
Q

Do Gram-negative have a ruffled or smooth appearance under a microscope?

A

Ruffled

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26
Q

Give an example of a species of bacteria that is Gram-positive

A

Staphylococci, streptococci, some listeria

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27
Q

Name a bacterial species that is Gram-negative

A

Enterobacter, salmonella, pseudomonas

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28
Q

What is the outer membrane of Gram-negative bacteria composed of?

A

Glycolipids called lipopolysaccharide

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29
Q

What does LPS cause?

A

Causes the endotoxic shock associated with the septicaemia caused by Gram-negative organisms

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30
Q

What are the 2 classes of the outer membrane in Gram-negative bacteria?

A

Lipoproteins and beta-barrel proteins

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31
Q

What do lipoproteins contain and what do they do?

A

They contain lipid moieties that are attached to an amino-terminal cysteine residue. These are thought to embed lipoproteins in the inner leaflet of the outer membrane

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32
Q

What do nearly all transmembrane proteins have in the outer membrane of Gram-negative bacteria?

A

A beta-barrel conformation

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33
Q

What are outer membrane proteins (OMPs)?

A

Unqiue membrane proteins that have a beta-barrel fold

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34
Q

What do OMPs do?

A

Have key roles in cell structure and morphology, nutrient acquisition, colonisation and invasion, and protection against external toxic threats such as antibiotics

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35
Q

What are some examples of OMPs?

A

Porins, OmpF, OmpC

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36
Q

What do some OMPs allow the passive diffusion of?

A

Small molecules (e.g. mono and disaccharides and amino acids) across the outer membrane

37
Q

What are the 2 key features of bacteria that lead to the different colours in gram staining?

A

The thickness of the peptidoglycan layer and the presence or absence of the outer lipid membrane

38
Q

What does gram staining stain?

A

The internal contents, not the cell wall

39
Q

What is the cytoplasmic membrane composed of in bacteria?

A

Typical phospholipid bilayer and various types of proteins

40
Q

Which proteins are contained within the cytoplasmic membrane of bacteria?

A

Integral membrane proteins (span the membrane) and lipoproteins

41
Q

What 4 things is the cytoplasmic membrane stabilised by?

A

Hydrogen bonds, hydrophobic reactions, and cations such as Mg2+ and Ca2+

42
Q

What process does the cytoplasmic membrane have an important role in and why?

A

Respiration because it occurs in the cytoplasmic membrane

43
Q

What are 3 functions of the cytoplasmic membrane?

A
  • Permeability barrier
  • Protein anchor
  • Energy generation
44
Q

What does the permeability barrier function of the cytoplasmic membrane do?

A

Prevents leakage outwards and functions as a gateway for the transport of nutrients into and out of the cell

45
Q

What role does the protein anchor function of the cytoplasmic membrane play?

A

It is the site of many proteins involved in transport, bioenergetics and chemotaxis

46
Q

Why is the energy generation function of the cytoplasmic membrane important?

A

It is the site of the proton motive force that produces energy used in transport, motility, and ATP generation

47
Q

What are 2 functions of the peptidoglycan layer of Gram-negative and Gram-positive bacteria?

A

Provides shape and rigidity to the cell, and withstands the substantial turgor pressure within the bacterial cell and prevents osmotic lysis

48
Q

The peptidoglycan layer is composed of thin sheets of 2 sugar derivatives. What are these?

A

N-acetylglucosamine and N-acetylmuramic acid

49
Q

How are the 2 sugar derivatives of the peptidoglycan layer linked together?

A

They are linked together alternatively to form glycan chains

50
Q

How are glycan chains linked?

A

By beta (1,4)

51
Q

Describe the structure of peptidoglycan layer in terms of glycan chains

A

Glycan chains are cross-linked via short chains of 4 amino acids (tetrapeptides) that are connected to the N-acetylmuramic acid residues

52
Q

What is the significance in how glycan chains are cross-linked in Gram-negative/positive bacteria?

A

How they are linked differs in Gram-negative and Gram-positive

53
Q

What is the strength of the peptidoglycan layer determined by?

A

The degree of cross-linking of the glycan chains (more = stronger, which is why gram-positive have a thicker layer because they have more cross-linking)

54
Q

The amount of peptidoglycan in the Gram-negative and Gram-positive cell wall differs. What percentage does each have?

A

In Gram-negative, the cell wall is 10% peptidoglycan and the rest is outer membrane. In Gram-positive, 90% is peptidoglycan and the rest is teichoic and lipoteichoic acid

55
Q

Describe the structure of the Gram-positive cell wall

A

Multi-layered sheets of peptidoglycan with teichoic acid and lipoteichoic acid inserted into them

56
Q

What proteins will you find in the cell wall of Gram-positive bacteria and what are their functions?

A

Cell wall associated proteins which function for transport and interacting with the host

57
Q

What are teichoic and lipoteichoic acids?

A

Acidic polysaccharides embedded in the peptidoglycan

58
Q

What is teichoic acid?

A

A polymer consisting of repeating glycerol or ribitol residues (up to 30 units) joined by phosphodiester linkages (may also have D-alanine and other sugars attached)

59
Q

What are lipoteichoic acids composed of?

A

Contain glycerol and are bound to the cell membrane via a diacylglycerol

60
Q

What are the 4 main constituents of the outer membrane?

A

Phospholipids, lipopolysaccharide, major proteins (e.g. porins, OmpA), and minor proteins (e.g. transport proteins)

61
Q

What type of bacteria have outer membranes?

A

Gram-negative

62
Q

Which leaflet in the outer membrane, out of inner and outer, are phospholipids found in?

A

The inner leaflet

63
Q

What is found in the outer leaflet of the outer membrane?

A

Lipopolysaccharide

64
Q

Which proteins are transmembrane and span both the inner and outer leaflets of the outer membrane?

A

OmpA and transport proteins

65
Q

What is unique about transmembrane proteins in the outer membrane of Gram-negative bacteria and why?

A

In Gram-negative bacteria, transmembrane proteins have a beta-barrel structure, whereas all others have an alpha-helical structure

66
Q

What part of the transmembrane proteins in the outer membrane allow bacteria to interact with the host?

A

Their exposed ‘loops’ of variable lengths

67
Q

What are 4 functions of the outer membrane?

A
  1. Forms an impermeable barrier around the bacteria
  2. Involved in the transport of materials into and out of the cell
  3. Keeps proteins and enzymes within the periplasmic space
  4. Interacts with the host
68
Q

Describe the structure of porin proteins

A

Consist of 3 transmembrane protein subunits

69
Q

What do porin proteins form through the membrane?

A

Small water-filled channels (pores) that are approximately 1nm in diameter

70
Q

What do the water-filled pores that porin proteins form in the outer membrane allow?

A

Diffusion of small hydrophilic molecules (sugars and other nutrients) across the impermeable outer membrane

71
Q

Give 2 examples of porin proteins in E. coli

A

OmpC and OmpF

72
Q

What function does the OmpA protein have?

A

Maintaining structural integrity of the outer membrane as it binds the outer membrane to the peptidoglycan layer

73
Q

Why does the OmpA protein have high specificity in its adherence via external loops?

A

Because of the amino acid sequences at the loop tips

74
Q

Which protein can act as a bacteriophage receptor?

A

OmpA

75
Q

Does OmpA form a pore through the outer membrane?

A

No

76
Q

What is the function of transport proteins?

A

Moving nutrients into the cell and various molecules out of the cell

77
Q

What are the 3 major features of transport proteins?

A
  • External loops involved in binding to receptors
  • Transmembrane pores through which molecules pass
  • Internal “plug” which acts as a “gate” and requires energy
78
Q

What structure do transport proteins have?

A

A beta-barrel structure

79
Q

What is the difference between transport proteins and porin proteins?

A

The pore in transport proteins is usually closed by a gate until the molecule passes through, whereas molecules diffuse constantly in porin proteins

80
Q

What allows the molecules to pass through the “gate” in transport proteins?

A

The energy of the proton motive force

81
Q

What are the 3 components that make up the lipopolysaccharide structure?

A

Lipid A, a core polysaccharide, and an O-antigen polysaccharide

82
Q

What is the structure of the O-antigen polysaccharide in lipopolysaccharides?

A

Made of 4-7 sugar groups, highly variable due to the variation of sugars possible

83
Q

What important function does the O-antigen of polysaccharides have?

A

Involved in immune evasion

84
Q

What does lipopolysaccharide provide resistance to in the gut and how does this help bacteria?

A

Bile salts - it protects the bacteria from being digested

85
Q

What is an important feature of Lipid A?

A

It is highly toxic

86
Q

What are bacterial capsules composed of?

A

Polysaccharides, protein, or a combination of the two (glycoproteins)

87
Q

What is bacterial capsule diversity responsible for?

A

Serotyping schemes

88
Q

Where are bacterial capsules produced?

A

External to the cell wall

89
Q

Name 4 functions of bacterial capsules

A
  1. Allows bacteria to resist desiccation due to their high water content
  2. Resistance to phagocytosis
  3. Resistance ro complement-mediated bactericidal effects of serum
  4. Evasion of host immune response

Microbiology & Immunology (5 decks)

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