Fundamentals in Microbiology Flashcards
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
2
Q
What do eukaryotes have that bacteria (prokaryotes) lack?
A
Histones
3
Q
What is an operon?
A
A cluster of many genes encoding enzymes of a single biochemical pathway
4
Q
What kind of genes do bacterial chromosomes contain?
A
Housekeeping genes
5
Q
What are housekeeping genes?
A
Genes that are essential for the maintenance of cells - e.g. for transport and replication
6
Q
Where are housekeeping genes located?
A
On the chromosome
7
Q
What are pathogenicity islands?
A
Distinct genetic elements on the chromosomes of a large number of bacterial pathogens
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
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
10
Q
What are some bacteria that have pathogenicity islands?
A
Salmonella, shigella, enteropathogenic E. coli, staphylococcus aureus
11
Q
What do DNA polymerases do?
A
Catalyse the addition of nucleotides
12
Q
Which organisms are plasmids found in?
A
Prokaryotes
13
Q
Do plasmids replicate independently of the host chromosome?
A
Yes, they possess their own origin of replication so can replicate independently
14
Q
Name an example of a function of a plasmid
A
Antibiotic resistance
15
Q
What type of antibiotic is penicillinase?
A
A beta-lactamase
16
Q
What do beta-lactamases do?
A
They split the beta-lactam ring inactivating the antibiotic penicillin
17
Q
What are the 4 main mechanisms bacteria use to acquire new traits?
A
- Genetic rearrangement (point mutations, insertion, deletions, etc.)
- Natural transformation (uptake and incorporation of naked DNA)
- Conjugation (genetic exchange between bacteria)
- Transduction (exchange occurs as consequence of phage predation)
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
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
20
Q
Is the peptidoglycan layer thicker in Gram-positive or Gram-negative bacteria?
A
Gram-positive
21
Q
What colour are Gram-positive bacteria when stained?
A
Purple
22
Q
What colour are Gram-negative bacteria when stained?
A
Pink
23
Q
Are teichoic and lipoteichoic acids present on Gram-negative or Gram-positive bacteria?
A
Gram-positive
24
Q
Do Gram-positive bacteria look smooth or ruffled under a microscope?
A
Smooth
25
Do Gram-negative have a ruffled or smooth appearance under a microscope?
Ruffled
26
Give an example of a species of bacteria that is Gram-positive
Staphylococci, streptococci, some listeria
27
Name a bacterial species that is Gram-negative
Enterobacter, salmonella, pseudomonas
28
What is the outer membrane of Gram-negative bacteria composed of?
Glycolipids called lipopolysaccharide
29
What does LPS cause?
Causes the endotoxic shock associated with the septicaemia caused by Gram-negative organisms
30
What are the 2 classes of the outer membrane in Gram-negative bacteria?
Lipoproteins and beta-barrel proteins
31
What do lipoproteins contain and what do they do?
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
32
What do nearly all transmembrane proteins have in the outer membrane of Gram-negative bacteria?
A beta-barrel conformation
33
What are outer membrane proteins (OMPs)?
Unqiue membrane proteins that have a beta-barrel fold
34
What do OMPs do?
Have key roles in cell structure and morphology, nutrient acquisition, colonisation and invasion, and protection against external toxic threats such as antibiotics
35
What are some examples of OMPs?
Porins, OmpF, OmpC
36
What do some OMPs allow the passive diffusion of?
Small molecules (e.g. mono and disaccharides and amino acids) across the outer membrane
37
What are the 2 key features of bacteria that lead to the different colours in gram staining?
The thickness of the peptidoglycan layer and the presence or absence of the outer lipid membrane
38
What does gram staining stain?
The internal contents, not the cell wall
39
What is the cytoplasmic membrane composed of in bacteria?
Typical phospholipid bilayer and various types of proteins
40
Which proteins are contained within the cytoplasmic membrane of bacteria?
Integral membrane proteins (span the membrane) and lipoproteins
41
What 4 things is the cytoplasmic membrane stabilised by?
Hydrogen bonds, hydrophobic reactions, and cations such as Mg2+ and Ca2+
42
What process does the cytoplasmic membrane have an important role in and why?
Respiration because it occurs in the cytoplasmic membrane
43
What are 3 functions of the cytoplasmic membrane?
- Permeability barrier
- Protein anchor
- Energy generation
44
What does the permeability barrier function of the cytoplasmic membrane do?
Prevents leakage outwards and functions as a gateway for the transport of nutrients into and out of the cell
45
What role does the protein anchor function of the cytoplasmic membrane play?
It is the site of many proteins involved in transport, bioenergetics and chemotaxis
46
Why is the energy generation function of the cytoplasmic membrane important?
It is the site of the proton motive force that produces energy used in transport, motility, and ATP generation
47
What are 2 functions of the peptidoglycan layer of Gram-negative and Gram-positive bacteria?
Provides shape and rigidity to the cell, and withstands the substantial turgor pressure within the bacterial cell and prevents osmotic lysis
48
The peptidoglycan layer is composed of thin sheets of 2 sugar derivatives. What are these?
N-acetylglucosamine and N-acetylmuramic acid
49
How are the 2 sugar derivatives of the peptidoglycan layer linked together?
They are linked together alternatively to form glycan chains
50
How are glycan chains linked?
By beta (1,4)
51
Describe the structure of peptidoglycan layer in terms of glycan chains
Glycan chains are cross-linked via short chains of 4 amino acids (tetrapeptides) that are connected to the N-acetylmuramic acid residues
52
What is the significance in how glycan chains are cross-linked in Gram-negative/positive bacteria?
How they are linked differs in Gram-negative and Gram-positive
53
What is the strength of the peptidoglycan layer determined by?
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
The amount of peptidoglycan in the Gram-negative and Gram-positive cell wall differs. What percentage does each have?
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
Describe the structure of the Gram-positive cell wall
Multi-layered sheets of peptidoglycan with teichoic acid and lipoteichoic acid inserted into them
56
What proteins will you find in the cell wall of Gram-positive bacteria and what are their functions?
Cell wall associated proteins which function for transport and interacting with the host
57
What are teichoic and lipoteichoic acids?
Acidic polysaccharides embedded in the peptidoglycan
58
What is teichoic acid?
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
What are lipoteichoic acids composed of?
Contain glycerol and are bound to the cell membrane via a diacylglycerol
60
What are the 4 main constituents of the outer membrane?
Phospholipids, lipopolysaccharide, major proteins (e.g. porins, OmpA), and minor proteins (e.g. transport proteins)
61
What type of bacteria have outer membranes?
Gram-negative
62
Which leaflet in the outer membrane, out of inner and outer, are phospholipids found in?
The inner leaflet
63
What is found in the outer leaflet of the outer membrane?
Lipopolysaccharide
64
Which proteins are transmembrane and span both the inner and outer leaflets of the outer membrane?
OmpA and transport proteins
65
What is unique about transmembrane proteins in the outer membrane of Gram-negative bacteria and why?
In Gram-negative bacteria, transmembrane proteins have a beta-barrel structure, whereas all others have an alpha-helical structure
66
What part of the transmembrane proteins in the outer membrane allow bacteria to interact with the host?
Their exposed 'loops' of variable lengths
67
What are 4 functions of the outer membrane?
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
Describe the structure of porin proteins
Consist of 3 transmembrane protein subunits
69
What do porin proteins form through the membrane?
Small water-filled channels (pores) that are approximately 1nm in diameter
70
What do the water-filled pores that porin proteins form in the outer membrane allow?
Diffusion of small hydrophilic molecules (sugars and other nutrients) across the impermeable outer membrane
71
Give 2 examples of porin proteins in E. coli
OmpC and OmpF
72
What function does the OmpA protein have?
Maintaining structural integrity of the outer membrane as it binds the outer membrane to the peptidoglycan layer
73
Why does the OmpA protein have high specificity in its adherence via external loops?
Because of the amino acid sequences at the loop tips
74
Which protein can act as a bacteriophage receptor?
OmpA
75
Does OmpA form a pore through the outer membrane?
No
76
What is the function of transport proteins?
Moving nutrients into the cell and various molecules out of the cell
77
What are the 3 major features of transport proteins?
- External loops involved in binding to receptors
- Transmembrane pores through which molecules pass
- Internal "plug" which acts as a "gate" and requires energy
78
What structure do transport proteins have?
A beta-barrel structure
79
What is the difference between transport proteins and porin proteins?
The pore in transport proteins is usually closed by a gate until the molecule passes through, whereas molecules diffuse constantly in porin proteins
80
What allows the molecules to pass through the "gate" in transport proteins?
The energy of the proton motive force
81
What are the 3 components that make up the lipopolysaccharide structure?
Lipid A, a core polysaccharide, and an O-antigen polysaccharide
82
What is the structure of the O-antigen polysaccharide in lipopolysaccharides?
Made of 4-7 sugar groups, highly variable due to the variation of sugars possible
83
What important function does the O-antigen of polysaccharides have?
Involved in immune evasion
84
What does lipopolysaccharide provide resistance to in the gut and how does this help bacteria?
Bile salts - it protects the bacteria from being digested
85
What is an important feature of Lipid A?
It is highly toxic
86
What are bacterial capsules composed of?
Polysaccharides, protein, or a combination of the two (glycoproteins)
87
What is bacterial capsule diversity responsible for?
Serotyping schemes
88
Where are bacterial capsules produced?
External to the cell wall
89
Name 4 functions of bacterial capsules
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
