Microorganism Diversity and Biology Flashcards
(387 cards)
1
Q
How are membranes linked in bacteria?
A
ester-linked
2
Q
What is the function of the microbiome ?
A
Development of the intestinal immune system, homeostasis, prevents colonisation of bacterial pathogens, effects on extra-intestinal autoimmune diseases
3
Q
What is the nucleoid ?
A
Nucleoid: DB DNA, circular chromosomes, negatively supercoiled, 1 set of each gene
4
Q
What are the ribosomes liked in bacteria ?
A
70S (30S + 50S)
5
Q
Why is 16S RNA sequencing good for phylogenetic studies ?
A
low mutation rate
6
Q
What is the uses of membranes?
A
o Anchor for 200 types of proteins
o Osmotic barrier
o Transport for solute
o Respiratory electron transport
o Synthesis of lipids and wall polymers
o Protein secretion
o Help determine shape and cell division
o Detection of environmental cues like nutrients
7
Q
What is the use of bacterial cell walls ?
A
o Resist osmotic pressure and determines shape
o Signal to the innate immune system of bacterial presence
8
Q
Gram negative cell wall
A
outer membrane then peptidoglycan in the periplasmic space and then cell membrane
9
Q
Gram positive cell wall
A
many layers of peptidoglycan then the cell membrane
10
Q
Gram staining
A
fixation –> crystal voilet –> iodine –> decoloriation –> safranin
positive traps CV and stains purple and negative decolorises and stains pink with the safranin
11
Q
Acid-fast cell envelop
A
Mycobacterium spp.
Large amounts of wax mycolic acids
Mycolic acids long, branched and complex fatty acids
Hydrophobic layer impenetrable to many harsh chemicals, disinfectants, strong acids
Reduced rate of nutrient uptake
12
Q
Layers of peptidoglycan in positive and negative
A
- Thick in gram positive (20-25 layers), thin in gram – (1-3 layers)
13
Q
What do lysozymes target ?
A
peptidoglycan, leading to lysis
14
Q
How do bacteria evade lysozymes ?
A
- Some bacteria have evolved to evade this TB amidation of glutamic acid or pneumonia has N-deacetylation of sugars so reduced inflammasome activation
15
Q
What acid is present in gram positive cell walls ?
A
Teichoic acids (TA)-
Chains of glycerol phosphate/ribitol phosphate, bound covalently with the peptidoglycan, provide rigidity, role in cell morphology and division, major surface antigen
o Promotes biofilm formation, adherence to host cell, proinflammatory response through toll-like receptors
16
Q
Is there any teichoic acid in gram negative cell walls ?
A
no
17
Q
Whats in the inner and outer leaflet of bacteria cell walls ?
A
- Outer membrane:
o Inner leaflet: phospholipids
o Outer leaflet: lipopolysaccharide (LPS)
18
Q
Whats in the periplasm of bacteria cell walls ?
A
transport systems for iron, proteins and other metabolites, hydrolytic enzymes break down large molecules, virulence factors like collagenases, proteases and beta-lactamase
19
Q
LPS cause ?
A
- LPS causes fever endotoxin, O-polysaccharide contributes to somatic antigens
o Essential for viability, O-polysaccharides repel hydrophobic molecules that could otherwise penetrate the membrane like antibiotics
o Small hydrophilic molecules can enter freely like porins
o LPS is used to class bacteria, O antigen serotypes of Escherichia coli
20
Q
What is a plasmid ?
A
Plasmid: circular or linear extrachromosomal DNA, not essential, capable of autonomous replication, often provide a selective advantage e.g., antibiotic resistance
21
Q
What is the flagella ?
A
Flagella: provide motility, arrangement and number of flagella is a characteristic of the genus, proton motive force used for energy
- Long helical filaments extend outside the cell
o The filament is hollow, single protein is called flagellin, most expose part highly antigenic (PAMP) H antigen
- Connecting hook
- Basal body motor to turn the flagellum
22
Q
What is pili and fimbriae ?
A
protein spikes that extend from the surface, pilli are typically longer than fimbriae, fimbriae are normally more abundant per cell than pili
- Adhesion: type 1 fimbriae allow E. coli to adhere to urethra to cause a UTI
- Twitching motility: type IV pili, extend and restrict to allow vibrio cholerae to move along a surface
23
Q
What is the role of sex pili ?
A
DNA transfer in conjugation
24
Q
What is the capsule ?
A
amorphous (not a defined shape) polysaccharide slime surrounding cells
- Tightly bound to the cell wall
- Can be present in both grams
- Observed under a light microscope with a specific stain
- Barrier to toxic hydrophobic molecules e.g., detergents
- Contain water prevents desiccation
- Presence and composition are strain-specific
25
What is the significance of the capsule in streptococcus pneumoniae ?
makes it virulent, resistant to phagocytosis and adheres to epithelial cells
26
What are some key macronutrients and their role ?
o Carbon: molecular building block
o Nitrogen: protein and nucleic acid, mainly inorganic (ammonia, nitrate, nitrogen
o Phosphorus: phospholipids and nucleic acids
o Sulphur: cysteine, methionine, vitamins, Co-A
o Potassium: enzymes
o Magnesium: stabilize ribosomes, membranes, nucleic acids
o Calcium: stabilize cell walls
27
What are some growth factors ?
o Small amounts of vitamins, amino acids, purines and pyrimidines
28
What are some micronutrients and their use ?
o Iron: cytochrome and electron transport proteins (siderphores: bind and transport of iron)
o Boron: auto-inducer for quorum sensing
o Zinc: enzymes
o Copper: respiration, cytochrome C oxidase
29
facilitate diffusion
pores and channels
30
Ion-coupled transport
(active transport):
- Symport – ion in the same direction as the transported molecule
- Antiport – ion in a different direction as the transported molecule
31
PTS system
activate transport, through translocators, transform another molecule in order to transport
32
ABC transport
active transport, uses ATP for transport
ATP-binding cassette, hydrolysis of ATP transport, specific binding proteins
33
Passive diffusion
- Simple: through membrane: small hydrophobic molecules like oxygen, carbon dioxide, ammonia, water
- Facilitated diffusion: Hydrophilic molecules require channel or carrier proteins
34
What are the 3 types of active transport ?
proton symport, ABC transport, group translocation
35
proton symport
driven by the electrochemical trans-membrane proton gradient (proton motive force)
o Co-transport in the same direction, hence ‘symport’
o E. coli lactose permease, lacy
36
Group translocation
substrate modified, generally phosphorylated, during transport
o PTS system
o The energy is provided by the PEP passed along chain of enzymes
o Modification of the sugar maintains concentration gradient
37
E. coli metabolism
- E. coli has 81 transcription factors and 41 target the central carbon metabolism pathways metabolic versatility
- Gluconeogenesis and TCA essential when E. coli infects the urinary tract
- Glycolysis and entner-doudoroff pathway growth in the intestinal tract
- The plateau in the growth curve is due to the bacteria adapting to a varying supply of carbon sources in the different niches
38
What is listeria
gram positive rods
- Food-borne with a 30% motility rate
- Utilization of host sugar phosphates via specific transporter activated in the host (Hpt)
- Promote rapid intracellular growth
39
What does all metabolic pathways lead to ?
pyruvate
40
How does aerobic respiration work in bacteria ?
- Similar to mitochondria
- Dehydrogenase, quinones, cytochromes and one or more terminal oxidases
- Electron transfer between components is possible by the presence of components that can exist in oxidised or reduced form such as hemes, iron-sulfur clusters
- The final electron acceptor is molecular oxygen (O2)
41
How does anaerobic respiration work in bacteria ?
- The final electron acceptor is an inorganic compound other than O2
- NO3- (nitrate) is reduced to NO2- (nitrite) via Nitrate reductase (NR)
- Reductase instead of cytochrome
- The total ATP yield is less because only part of the krebs cycle operates under anaerobic conditions and due to the less redox potential of the final electron acceptor.
42
What is fermentation?
- Release energy from oxidation of organic molecules
- Does not use the krebs cycle or the electron transport chain
- Derives ATP from substrate-level phosphorylation
- Does not require oxygen (anaerobic process)
- Recycle NADH back to NAD+
43
What is the preference order of metabolism ?
aerobic --> anaerobic --> fermentation
44
Characteristics of mycobacterium tuberculosis ?
Mycobacterium tuberculosis: acid-fast rods, non-motile, strictly pathogenic, gram positive, facultative intracellular, dormancy
- Captured by macrophage
- Manipulates the vesicle to evade killing, therefore it replicates inside the macrophage
- Forms granuloma then fibrin (captures other immune cells) then encapsulated
- Then is released from the macrophage before the macrophage is detected and destroyed
45
What is the essential carbon sources during infection ?
host cell lipids
46
How does bacteria avoid carbon loss during oxidation in the TCA cycle ?
Switch from carbohydrate-based metabolism to the metabolism of lipid structures via the glyxolate shunt enzyme isocitrate lyase (avoid carbon loss during oxidation in the TCA cycle)
- Specific substrates are used at different stage of infection
- Microaerophilic will move the electrons to a cytochrome with a higher oxygen-affinity
47
Binary fission >
Binary fission:
1) Elongation of cell wall, cell membrane and overall volume
2) Start chromosome duplication
3) Septum wall grows inwards
4) Chromosomes are pulled towards opposite ends
5) Septum is synthesized
6) Cell membrane separates the cell chambers
48
How do actinomycetes reproduce ?
conidiospores
49
What is FTS ?
(Filamentous temperature sensitive)
- E. coli (gram -) divide at 37C, weird division at 42C (uneven shapes and sizes, start to filament)
- Fts proteins interact to form the divisome
50
Divisome
a cell division apparatus forms the septal ring and defines the cell division plane
- The ring is formed at the centre from other protein synthesis occurring at the equator of the cell
- Fts1 is a penicillin binding protein, that can block binary fission
51
MinCDE ?
(Min proteins):
- Cytoskeletal-like coiled in the poles
- Bipolar gradient that helps to localize the ring
- These proteins accumulate at one side allowing for one cell to split from the other, this prevents the septum ring from forming at the poles
52
DnaA
binds to the DNA origin of replication (oriC) to initiate formation of the DNA replication complex
53
Endospore formation
- Survival mechanism triggered by adverse conditions
- Endospores: resting stages highly resistant to heat, desiccation, etc
- May survive thousands of years
- Bacterial genome is sequestered in a safe place (spore) until environment conditions improve
Mother cell secretes protein coat (calcium dipicolinate) to protect spore then lyses releases the spore
54
Features of an endospore
- core: DNA, RNA, proteins
- inner membrane: lipids/proteins
- wall: peptidoglycan
- cortex: modify peptidoglycan (Ca++) – keratin – reverse osmosis to create dehydrate structure
- outer membrane: lipids/proteins
- coat: proteins
- exosporium: proteins
55
Dipicolinic acid
Dipicolinic acid --> form complex with Ca++ --> bind water --> spore became drier and compact
56
vegetative cells vs endospores
vegetative cells - gram positive, nonrefractile, absent calcium dipicolinic acid, low heat resistance, low radiation resistance, sensitive to lysozymes, sensitive to staining
endospores - no S- layer, refractile, dipicolinic acid in the core, very low water activity, high resistance to heat, lysozymes and chemicals, resistant to stains.
57
Where are endospores made ?
gram positive cells
58
Role of protein secretion in bacteria ?
- key role in modulating bacteria interactions with their environment
- mutualistic and pathogenic associations secreted protein enter inside host cells modify host physiology necessary for bacterial survival e.g., promote colonization of host (toxins and effector proteins)
59
Sec, TAT
Sec (general secretion)
- ubiquitous (found in every cell) and essential
- main route oof protein export
- requires a signal peptide/leader sequence
TAT (Twin-arginine translocation)
- not as widespread
- normally transports fewer substrates than the sec system
60
Translocase
selection of SecA, SecE, SecY and SecG
- Sec system secretes unfolded proteins using ATP on the translocase
- Tat system secrete folded protein using proton motive force, TatA (numerous) transports the proteins, TatB and TatC allow for proton transfer
61
How does secretion work in +ve and -ve
direct in +ve
2 steps in -ve, - Requires 2 steps, the second step translocation across outer membrane
- TxSS system (type x secretion system)
- Type 2SS, T5SS, T8SS, T9SS
62
Type II secretion system (T2SS)
- Also known as the Sec-dependent (requires the Sec protein)
- Importance in cell physiology and virulence
- Role in pilus biogenesis
- Required for virulence for human pathogens e.g., vibrio cholerae
- Complex system 12-15 proteins
Vibrio cholerae: free dwelling organism, in humans and in water, no human-to-human transmission
63
T1SS
Gram negative: T1SS, doesn’t require 2 steps, proteins move from the cytoplasm to the outside of the cell
- double-membrane- spanning export system
- translocate substrates in one step across two membranes
- virulence factors such as pore-forming toxins, adhesions proteins, etc. secreted via the T1SS
- uropathogenic (urinary tract) strains of E. coli haemolytic toxin called HlyA
64
What secretion systems in gram negative bacteria are one or 2 step processes?
So in gram negative, T2SS is 2 step, T1SS, T3SS, T4SS, T6SS is one step
65
T3SS
- injectisomes molecular syringes
- gram -ve interact with animal host (pathogenic or mutualistic)
- deliver effector proteins to the cytosol of the host cell
- modulate a large variety of host cell functions (immune and defence responses)
- samolnoella, pseudomonas
66
Parts of an injectisome
Translocon – a tup complex at the distal end
Needle complex – membrane-anchored base protruding needle filament
Basal body – several inner membrane proteins
Cytoplasmic sorting platform: large cytoplasmic multiple-protein complex that orderly selects and delivers the substrates to the export apparatus
67
Effector targets in host cells
- cytoskeleton
- T-junctions barrier function
- Cell cycle
- Inflammatory responses
- Mitochondrial function
- Apoptosis
68
T3SS-1 vs T3SS-2
- T3SS-1:
o Early phase invasion of enterocytes and M-cells
o Activation of proinflammatory responses
- T3SS-2:
o Later phase of infection
o Intracellular survival and replication within macrophages
69
Type IV secretion systems - T4SS
- DNA and protein transfer
- Target cells animal cells and bacteria
- Gram positive and negative
- T4SS may require up to 25 different proteins
- Role in pathogenesis
Contact-dependent interbacterial
Contact-independent DNA uptake and release
70
Type VI secretion system – T6SS
- Protein transfer
- Target cells animal host cells and bacteria
- Role in pathogenesis
- Translocates effector proteins into target cells in one-step manner
- Contractile nanomachine several protein subcomplexes
- Dynamic firing cycles: assembly, contraction and disassembly of a sheath-like structure expulsion of a cell-puncturing device loaded with multiple toxins.
71
Type VII secretion system - T7SS in mycobacterium tuberculosis
- ATPase-driven export
- 5 distinct T7SS (ESX-1 to ESX-5)
- Major secretion pathway for approx. 200 proteins
- Interactions with host cells and modulation of the immune system
- Obligate – always needs a host
- Involved in pathogenesis attenuation of the current live vaccine BCG mainly attributed to an inactivating deletion of ESX-1 T7SS
72
How does our immune system differentiate between commensal and pathogenic E. coli ?
T3SS is only attributed to pathogenic E. coli, so that’s how our immune system recognises commensal and pathogenic E. coli.
73
How do commensals help prevent infection ?
- Prevent pathogen colonization
- Out-compete pathogens
- Produces antimicrobial compounds
- Microbiome “educates the immune system”
- Gut-associated commensals provide important nutrients
74
How do commensals have harmful effects ?
- Displaced commensals – can cause infection
- Antibiotic-induced dysbiosis e.g., clostridium difficile
- Conversion of commonly ingested food substances into carcinogenic substances
- Immunocompromised hosts
75
What changes can occur in the flora ?
- With changes in hormonal physiology and development
- When antibiotics select for a ‘resistant flora’
- New organisms may be acquired
76
how can we avoid clostridium difficile taking advantage of a reduce gut microbiota ?
stop precipitating antibiotics, oral medication, recovery requires re-establishment of normal flora (probiotics)
77
Koch's postulate
- The pathogen must be present in every case of the disease
- The pathogen must be isolated from the diseased host and grown in pure culture
- The specific disease must be reproduced when a pure culture of the pathogen is inoculated into a healthy susceptible host
- The pathogen must be recoverable from the experimentally infected host
78
Microbial pathogenicity factors
Toxins, adhesins, Iron uptake, LPS, Invasins, slime, enzymes, capsule
79
Endo/exo/entero toxins
o Exotoxin: secreted into the environment
o Endotoxin: LPS in gram negative bacteria
o Enterotoxin – an exotoxin that is effective in the gastrointestinal tract
80
Adhesins
hair-like structure (mono or poly-trichous), allows movement from one site to another, example of a PAMP
o Gram negative:
Fimbriae – protein subunits, interact with eukaryotic cells
Pilli – longer than fimbriae, 1 present on the surface, involved in conjugation (F-pillus)
o Gram positive:
Anchored either the cytoplasmic membrane or the cell wall
81
Invasins
proteases, glycosidases, nucleases, phospholipidase
82
steps in invasion
Breaking the barrier --> loose association --> adhesion
Colonisation: cell-wall associated proteins
Adherence – to the host cell, prevents being washed off, formation of a microcolony
83
Iron sequestering
- Iron is essential, limiting in host
- Sequestration is critical for in vivo success
- Produce iron binding compounds called siderophores
- Capture from the host and bind to the bacterial surface
84
How do bacteria protect itself
- Capsules – polysaccharide capsule, negative charged, slime
o Protects from desiccation and phagocytosis
- Teichoic acids – negatively charged
- Biofilms
LPS overstimulates cytokines leading to septic shock
LPS – most endotoxin molecule
85
How do commensals go to pathogenic ?
Genetic variation in bacteria: HGT turns commensals to pathogens
- Environmental response
- Niche adaptation – gene expression
- Host-mediated pathogenesis
1) Existing genetic factors chromosome, plasmid, mobile genetic elements (MGEs)
2) Genetic mechanisms (activated by the environment)
a. Regulatory networks LPS modification, Quorum sensing to form biofilms
Environmental signals can be transferred by transient-reactive or non-mutation, constitutive-mutational
86
Control of survival phenotype to avoid metabolic expenses
- Tailoring needs to the environmental niche
o Host environment – immune system dedicated to the prevention of infection
- Niche dependent – may inhibit more than one niche during the course of an infection
o E.g., attachment vs avoidance (intracellular vs extracellular)
87
Microbe-host interaction to promote survival
- Prevention of opsonization
- Toxin secretion can paralyze the hosts defences
- Disruption of mucosal integrity
- Chemokine production
- Microbial recognition and host response – cAMP
88
One component systems
toxins in cholorae
89
What signal tells a bacteria to grow ?
extra cytoplasmic function (ECF) alpha factors
90
signal cascade
- Signal – environmental change, signalling molecule
- Sensor – usually ligand-binding, able to change protein conformation for protein-protein interactions
- Regulator – usually specific DNA binding proteins, bind in control region
- Regulon – group of genes controlled by a common regulator
91
Bacterial regulons
- Catabolite repression
- DNA supercoiling
- SOS response to DNA damage
- Virulence
- Osmotic stress response
- Oxidative stress response
- Switch to anaerobic growth
- Sporulation
92
93
Phosphorelya
Phosphorelay – phosphate allows the protein to bind to the DNA, making it a regulator
- PhoQ, when magnesium and calcium are high the PhoQ isn’t activated, only activated when low.
- This allows proteins for peptide resistance, Mg2+ uptake and intramacrophage survival
94
Low weight inducer molecules
Low weight Inducer molecule – AHLs/AIPs
Gram negative – acyl-homoserine lactones (AHLs)
Gram positive – Autoinducing peptides (AIPs)
95
Which of the following is a key feature of the Mycobacterium cell envelope that contributes to its resistance to harsh environments?
mycolic acid
96
The type IV pili are involved in which of the following processes
twitching motility
97
Which transport system modifies the substrate during entry into the cell?
PTS system
98
In E. coli, which transport mechanism is used by the lactose permease (lacY) gene product?
symport using proton gradient
99
What gives flagella their rotational power in bacteria?
proton motive force
100
What type of metabolism doesnt require oxygen
fermentation
101
Which type of secretion system is involved in the transfer of folded proteins across bacterial membranes using a proton motive force?
TAT system
102
11. Which secretion system is responsible for injecting effector proteins into host cells during bacterial infections?
T3SS
103
What is the major function of the Type VI secretion system (T6SS) in bacteria?
to secrete toxins into the target cell
104
Which of the following secretion systems requires two steps for protein export in Gram-negative bacteria?
T2SS
105
Which environmental condition triggers the activation of Salmonella's SPI-2 virulence system?
Change in acidity detected by Toll-like receptors
106
What bacterial component is known for assisting with 'Twitching'?
Pili
107
Which yields more ATP = fermentation or glycolysis ?
glycolysis
108
Do spores produce calcium dipicolinate ?
Yes
109
What is the role of FtsZ during cell division ?
Forms a ring at the cell division site
110
Role of fimbriae
interact with eukaryotic cells or inert surfaces via receptors at the tip
111
Major difference in structure between pili and fimbriae ?
Fimbriae is composed of multiple subunits whereas pili are not
112
What type of molecule is a virus ?
Nucleoprotein
113
Viruses are metabolically ..
inert
114
size of a virus
10-400 nm
115
Nucleic acid + Capsid =
Nucleocapsid
116
What is the envelope in enveloped viruses?
lipid bilayer derived from the host, embedded with spike proteins
117
Viral genomes can be ...
DNA or RNA (never both), can be single-stranded (ss) or double-stranded (ds), linear or circular
118
What does a segmented genome mean?
A segmented viral genome means that the virus’s genetic material is split into multiple separate pieces (segments), instead of being one continuous strand
119
What is the capsids function ?
protect nucleic acid and aids transfer between or in hosts
120
What is the capsid made from ?
capsomere (subunits)
121
What are the 3 shapes that capsomere can arrange themself ?
Polyhedral (icosahedral)
Helical (cylindrical)
Complex
122
What does a naked virus look like ?
only a capsid with no envelope (lipid membrane)
123
What are some features of naked viruses ?
- More resistant to drying, heat, acid and detergents
- Uses direct endocytosis or entry
- Direct contact, fecal-oral, fomites
- Poliovirus, adenovirus, norovirus, rhinovirus
124
How do enveloped viruses gain entry ?
- Uses membrane fusion through bodily fluids
125
mRNA is what sense ?
positive
126
influenza has how many segments ?
8
127
How are viruses classified ?
- Structure, genome and replication properties
o This gives them their family
- Families subdivided into genera
- Subtypes based on nucleotide sequence and antigenic reactivities
o Like type 1 and type 2 of herpes virus
128
What is the baltimore classification?
describes the relationship between viral genome and mRNA
129
How are viruses cultured ?
tissue culture like chicken eggs
130
How are viruses quantified ?
plaque assay
131
What is the equation for PFU ?
- Plaque count x 1/dilution = plaque forming units (PFU) per unit volume of inoculate
132
What is CPE ?
Cytopathic effect (CPE) – changes to the host cell caused by a virus
- TCID50: tissue culture infectious dose 50%
- Quantity of virus required to produce signs of infection in 50% of cultures
133
What are the stages of viral replication ?
1) Adsorption (attachment)
2) Entry
3) Uncoating
4) Genome replication and transcription
5) Synthesis of virus components
6) Assembly
7) Release (and maturation)
134
how does the virus interact with the host ?
capsid or envelope holds specific proteins and receptors on the target cell (tropism)
135
Do viruses have the ability to infect all cells ?
No, only a specific number called host range
136
How do neutralising antibodies stop the virus gaining entry ?
Binding to the virion attachment protein to block the interaction
137
What are the 2 ways of entry for a virus ?
o Endocytosis
o Fusion of virus envelope with cell membrane
138
How does uncoating work in viral replication ?
- Release of viral genome
- Cell enzymes (lysosomes) strip off the virus protein coat
- Virion can no longer be detected; known as the ‘eclipse period’
- Uncoating can happen at the plasma membrane, endosome, nuclear membrane or nuclear membrane and a endosome
139
How does HIV attach ?
SU proteins bind to CD4 and a co-receptor is required which is a chemokine receptor, CXCR4 in T cells and CCR5 in macrophages
140
How does influenza enter and uncoating ?
- Low pH in the endosome
- Causes conformational change in hemagglutinin (glycoprotein)
- Allows fusion of the viral envelope with endosomal membrane allowing for uncoating and the viral genes to be excreted
141
How does SARS-CoV2 attach and enter ?
- S glycoprotein is cleaved by TMPRSS2
- Facilitates viral activation
- Essential host factors for pathogenicity
- TMPRSS2 is a target for antiviral drugs
142
Is poliovirus enveloped or not ?
not
143
How does polio get entry ?
- After receptors attach; virus is taken up into endosome, conformational changes to the structure
- Forms a pore in the endosome membrane
- Viral RNA is released into cytoplasm
144
Where does assembly occur ?
- May take place in cell nucleus, cytoplasm or (with most enveloped viruses) at the plasma membrane
145
How does the release work in non-enveloped viruses ?
- Sudden rupture of cell
146
How does the release work in enveloped viruses ?
- Gradual extrusion (budding) of enveloped viruses through the cell membrane
147
How does budding work ?
through virus-protein interactions leads to specific packaging of the genome
148
What is the role of the golgi and ER in virus replication ?
Golgi: creates the endosome with the viral glycoproteins on the intracellular membrane
ER: creates the glycoproteins
149
What is step 4 and 5 in viral replication ?
genome replication and protein expression
150
What is RNA dependent DNA polymerase also known as ?
reverse transcriptase
151
What do all RNA viruses encode ?
RNA dependent RNA polymerase
152
How does +ve RNA viruses replicate ?
genome acts as mRNA and is translated to produced polymerase
153
How does -ve RNA viruses replicate ?
o Need to carry the polymerase in the virion
o Required to convert -ve RNA +ve mRNA after entry
154
examples of dsDNA viruses
papillomaviridae, adenoviridae, Herpesviridae
155
examples of ssDNA viruses
circoviridae
156
How does a dsDNA virus replicate ?
dsDNA → mRNA → viral proteins
dsDNA → replicated → new viral genomes
✅ Uses host or viral DNA-dependent RNA polymerase
157
How does a ssDNA virus replicate ?
ssDNA → dsDNA (intermediate) → mRNA → viral proteins
dsDNA → new ssDNA genomes (positive and negative sense)
✅ Requires DNA synthesis before transcription
158
example of dsRNA virus
Reoviridae
159
How does a dsRNA virus replicate ?
dsRNA → mRNA (transcribed by viral RNA-dependent RNA polymerase)
mRNA → proteins
mRNA → replicated back to dsRNA for new genomes
✅ Genome replication and transcription inside viral particle to avoid host detection
160
How does a -ve ssRNA viruses replicate ?
−ssRNA → mRNA → viral proteins
mRNA → +RNA intermediate → −ssRNA genomes for packaging
✅ Must carry RNA-dependent RNA polymerase in the virion
161
Example of -ve ssRNA virus
Rhabdoviridae (e.g., Rabies virus)
162
Example of +ve ssRNA virus ?
Coronaviridae (e.g., SARS-CoV-2)
163
How does a +ve ssRNA virus replicate ?
+ssRNA acts directly as mRNA → translated to proteins
+ssRNA → −RNA intermediate → more +ssRNA genomes
✅ No need to carry polymerase in virion (but synthesize it quickly after entry)
164
What viruses are ssRNA with a DNA intermediate ?
retroviridae (HIV)
165
How does ssRNA with a DNA intermediate replicate ?
+ssRNA → −DNA (by reverse transcriptase)
−DNA → dsDNA (integrated into host genome as provirus)
Host machinery: dsDNA → mRNA & +ssRNA genomes
mRNA → viral proteins
✅ Integration into host genome allows lifelong infection
166
What are some problems that RNA viruses have that DNA don't ?
o Eukaryotic cells do not have RNA dependent RNA polymerase
o Eukaryotic cells do not (usually) encode for more than one protein on each mRNA
167
How does poliovirus replicate its genome ?
Poliovirus: polyproteins (ssRNA virus) (+)
- One single ORF that encodes for a large polyprotein then cleaved by viral proteases
168
How does coronavirus replicate its genome ?
Coronavirus: multiple transcripts (ssRNA virus) (+)
- Produces multiple transcripts sing discontinuous transcription
169
How does influenza replicate its genome ?
Influenza virus: segmented genome (ssRNA) (-)
- 8 RNA segments, each encapsulated separately in the viral particle and transcribed separately in the host cell
170
What is genome reassortment ?
Genome reassortment leads to new strands being made:
- When segmented RNA viruses exchange gene segments when two or more strains infect the same host cell
- - influenza is a common example due to a segmented genome
171
How does HIV replicate its genome ?
- Diploid genome and replicates via a DNA intermediate
- Uses the host RNA polymerase to make a proviral DNA primary transcript
o Serve as genomic RNA for the new virion
o Unspliced mRNA for translation of structural proteins
o Spliced to form mRNA for regulatory and accessory proteins
Regulatory and accessory proteins control viral replication, immune evasion a host cell manipulation
172
What do anti-viral drugs target ?
o Attachment antagonists
o Inhibits uncoating
o Inhibit DNA/RNA synthesis
o Block maturation
173
What is epidemiology the study of ?
mode of transmission, age, gender, ethnic background, travel history, occupation, season, underlying health conditions
174
Can viruses transmit horizontally or vertically ?
both
175
When can transmission occur in the viral lifecycle ?
- With or without disease symptoms
- During asymptomatic shedding of virus
- During incubation period (before symptoms)
Transmission results in primary infection
Reactivation of some viruses can result in secondary disease
176
acute vs chronic vs latent infection
Acute infections: last less than a year, High amount of virus initially, soon decreases
Chronic infection: lasts longer than a year, amount of virus decreases over the years
Latent infection: reactivation years later of the virus, reactivation has smaller amounts of the initial infection’s virus
177
What effects do viruses have on the cell?
- Abortive infection, cpe, protein translation fault, apoptosis, transformation, PRR
178
What is transformation in terms of viral infection ?
affect on the cells behaviour, Immortalisation of cell – tumours
179
What does poliovirus do to the cell ?
- Shuts-off the cell’s protein translation
- Cleavage of ‘cap-binding complex’
- Viral 5’ UTR enters the ribosome allowing for viral translation
180
What does influenza do to the cell ?
- mRNA cap stealing
- allows translation of viral mRNA
- reduces expression of host proteins
181
What is the mechanism of apoptosis ?
- cell injury: DNA damage, protein misfolding
- effector mitochondria
- cytochrome c and other pro-apoptotic proteins
- executer capases destroy the cytoskeleton
- endonuclease activation
- bleb formation
- apoptotic body
- phagocytosis
Viruses may evade apoptosis or induce it
182
What are the 2 pathways to apoptosis ?
mitochondrial (intrinsic) pathway, death receptor (extrinsic) pathway
183
examples of transforming viruses
HPV, retrovirus, herpesviruses, Hepatitis B and C
184
What are some features of HPV ?
- Ubiquitous: Infection can be completely asymptomatic, commensal
- Cause papillomas (benign skin warts)
- Uterine cervix cancers
Genome: Double-stranded DNA (dsDNA)
Family: Papillomaviridae
Structure:
Non-enveloped (naked capsid)
Icosahedral capsid
185
What is the E6 and E7 genes in the HPV ?
The E6 and E7 genes of cancer-causing HPVs mediate destruction of the tumour-suppressor proteins p53 and pRB
186
What is the HPV vaccine ?
recombinant virus-like particles based on the HPV capsid
- Quadrivalent vaccine protects against HPV
- Elicits HPV – neutralizing antibody responses that protects against primary infection
- Nonvalent vaccine also protects against HPV
187
what is the cytokine storm ?
systemic inflammatory syndromes leading to hyperactivation of cytokine production throughout the immune system
188
what are some immune modulation strategies used by viruses ?
- Secreted modulators
o Cytokine/chemokine mimics and binders
- Modulators on infected cell surface
o Mimics/antagonists of immune signalling
- Stealth/latency
o Express few/no proteins
- Antigenic hypervariability
- Block adaptive immune response
- Inhibit complement
- Interfere with pattern recognition receptors (PRRs)
- Block interferons and/or infllamatory cytokines
189
Which virus has a DNA genome but replicates via an RNA intermediate?
Hepatitis B
190
Which virus replicates its genome in the nucleus despite being an RNA virus?
Influenza
191
Viral NS1 protein from influenza helps immune evasion by:
Blocking type I IFN production
192
Which virus downregulates MHC-I to escape CTL detection?
Epstein-Barr Virus (EBV)
193
What is the main mechanism by which vaccines protect against viruses?
Generating memory B and T cells
194
Which antiviral targets neuraminidase activity?
Oseltamivir
195
Which drug inhibits reverse transcriptase in HIV?
AZT (Zidovudine)
196
SARS-CoV-2 gains cell entry by binding:
ACE2
197
antigenic shift
Genetic reassortment between segmented genomes
198
Which viral feature contributes most to zoonotic potential?
Ability to use conserved host receptors
199
What is the common phenomenon in all viral infections?
mRNA synthesis
200
Which of these viruses has helical symmetry?
Influenza
201
Virus with icosahedral symmetry
Herpesvirus, picornavirus
202
In a one-step growth assay, the “Eclipse period” is...?
The time taken between infection of cell and the appearance of intracellular virus particles
203
Human Immunodeficiency virus (HIV) uses which of the following receptors for entry into Macrophages?
CD4 and CCR5
204
True or false: Some enveloped viruses fuse at the nuclear membrane
False
205
True or false:Viruses directly inject their genomes through the plasma membrane
false
206
True or false: Poliovirus assembles it’s capsid around the genome
false, Poliovirus forms a progeny virion, which involves genome replication and packaging into a pre-formed capsid rather than directly assembling around the genome in the sense of it happening immediately upon entry or early in the replication cycle
207
true or false: Maturation is catalysed by the viral protease enzyme
True, This protease cleaves the viral polyprotein into functional units
208
True or False: Maturation is catalysed by the viral reverse transcriptase
False
209
True or False: The HIV protease is a target for antiviral drugs
True
210
The Baltimore classification, classifies viruses based on the processes used for synthesising...
mRNA
211
Retroviruses encode for which of the following enzymes
RNA-dependent DNA polymerase (reverse transcriptase)
Protease
integrase
212
RNA viruses (other than retroviruses) encode for which of these polymerases?
RNA-dependent RNA polymerase
213
True or false: Eukaryotic cells encode for RNA-dependent RNA polymerase
false
214
Which immune evasion strategy does the herpes simplex virus (HSV) employ to avoid detection by MHC-I molecules?
HSV inhibits the peptide transporters that load viral peptides onto MHC-I
215
Retrovirus in baltimore classification ?
Retroviruses (RNA, positive sense) – replication occurs through reverse transcription
216
How does the adaptive immune system tackle viruses ?
B cells produce antibodies that can neutralize free viral particles
217
What mechanism do coronaviruses use to generate a variety of viral proteins from their RNA genome?
Ribosomal frame-shifting
218
What is the genome type and envelope status of Influenza?
-ssRNA, segmented genome, enveloped; replicates in the nucleus.
219
How does Influenza generate new variants?
Antigenic shift via reassortment of its 8 RNA segments during co-infection; and antigenic drift through point mutations.
220
What is the genome type of HIV, and what key enzyme does it use?
+ssRNA with reverse transcriptase (Class VI); also uses integrase and protease; enveloped
221
What is the replication strategy of HIV?
Reverse transcription of RNA into DNA → integrates into host genome → host machinery transcribes/replicates it.
222
What class is Rotavirus and what makes its genome unique?
Class III: dsRNA, segmented genome; uses RNA-dependent RNA polymerase packaged in virion.
223
How does Rotavirus replicate?
Replicates in cytoplasm using RdRp; avoids detection by hiding dsRNA in subviral particles.
224
What are key features of SARS-CoV-2?
+ssRNA genome, enveloped, uses spike (S) protein to bind ACE2, replicates in cytoplasm using viral RdRp.
225
How is SARS-CoV-2 translated and replicated?
Direct translation of +ssRNA; viral RdRp makes -ssRNA template to synthesize more genomes
226
What is the genome type and structure of Norovirus?
+ssRNA, non-enveloped, icosahedral; translated directly into viral proteins in cytoplasm
227
What enzyme must a -ssRNA virus carry?
Must carry its own RNA-dependent RNA polymerase (RdRp) to transcribe +mRNA
228
Which RNA virus replicates in the nucleus?
Influenza (unique among RNA viruses); allows access to host capping enzymes
229
Which DNA virus replicates in the cytoplasm and why?
Poxvirus; brings all its own replication machinery.
230
What is a obligate parasite ?
requires at least part of their life cycle in a parasitic relationship
231
What is a facultative parasite ?
free living but can become parasitic if they enter a suitable host e.g., plasmodium falciparum
232
What is a definitive host ?
where the parasite reaches sexual maturity
233
What is a intermediate host ?
a host that is required for parasite development but where no sexual development takes place
234
What is an incidental host ?
a host that can be infected but does not play a role in the life cycle
235
What is a paratenic host ?
no development takes place but the parasite remains alive and infective to another host
236
What is a helminth?
parasitic worms, cause many neglected tropical diseases e.g., intestinal worms, onchocerciasis, lymphatic filariasis
237
Parasitic worms (Helminths) are split into what 3 groups ?
Nematodes (roundworms), cestodes (tapeworms) and trematodes (flukes)
238
Example of a roundworm (nematode) ?
trichuris trichiura
239
example of a fluke (trematode) ?
schisosoma mansoni
240
Example of a tapeworm (cestode) ?
taenia solium
241
Helminths infect by ...
orally, through skin, or vector bite
242
Do helminths proliferate in the host ?
no, generally lay eggs in faeces or urine
243
What are some symptoms to intestinal helminths ?
- Abdominal pain
- Diarrhoea
- Malnutrition
- Protein deficiency
- Iron deficiency anaemia
- Growth reduction
- Neurological problems
244
What are some challenges to combating helminths ?
- Very good at evading and supressing host immunity
- Long-lived: they don’t want to kill their host
- Large size – hard to kill or dislodge
- Takes decades to develop immunity and protective memory
- Immune suppression is often associated with reduction in pathology
245
Why are helminths so good at manipulating its host ?
co-evolution
246
What is the whipworm ?
trichuris trichiura
- One of the most common helminthic infections
- Sexual reproduction occurs in the mammalian host
- Eggs ingested
- Larvae emerge in the duodenum
- Adults feed in the large intestine and the male and female’s mate
247
What does the whipworm lead to ?
Trichuris dysentery syndrome
- Infection may be asymptomatic
- Can cause diarrhoea, intestinal bleeding, iron deficiency
- Rectal prolapse
248
What are some filarial worms ?
- Wucheria bancrofti – lymphatic filariasis
- Onchocerca volvus – river blindness
249
What is Taenia solium ?
Taenia solium – tapeworm/cestode
- Animal eats ingested vegetation, we ingest infected meat
- Causes cysticercosis (occurs after ingesting of eggs from environment)
o Eggs develop into larvae in the gut, penetrate intestinal wall and encyst in muscle and CNS
o Symptoms can include brain and spinal cord pathologies:
Dizziness
Seizures
Epilepsy
250
What is the Schistosoma spp. ?
- Causes schistosomiasis
o Larvae and egg migrate through the body
o Inflammation
o Trapped in liver causing fibrosis
o Eggs may migrate to the CNS leading to spinal inflammation
o If migrate to female reproductive organs can lead to ectopic pregnancy or infertility, increase risk of HIV
251
What changes do protozoal parasites face when entering the host ?
- Infecting hosts and sometimes, specific host cells 0 may involve migration and parasite motility
- Undergo transmission
- Gaining nutrients – may need to adapt to different environments at different lifecycle stages
- Avoid being killed by the host
- Maintain a balance between proliferation, forming a long-term infection and undergoing transmission
252
In malaria what type of hosts are mosquitos ?
definitive
253
What is the sporozoite ?
injected into the human host when the mosquito feeds
254
What is the gametocyte ?
sexual stages that form in humans
255
What is the ookinete ?
formed from macrogametocytes and microgametocytes
256
What is toxoplasmosis ?
mild flu-like symptoms as a result of malaria
- Infection in pregnancy can lead to foetal encephalitis (inflammation of the brain)
- neuropathology in immune-compromised people
- intermediate host can be any mammal specie
- definitive host are cats (in their gut epithelium)
- transmission occurs via predation
- parasite forms in the brain, forms cysts
- transmission occurs via ingestion of contaminated faeces or meat containing the cyst
257
What is african trypanosomiasis ?
- transmitted by the tsetse fly (definitive host)
- causative agent of sleeping sickness in humans
- trypansoma brucei gambiense/rhodesiense
258
Whats the significance of trypansoma brucei ?
has only a extracellular stage
259
What are the advantages to plasmodium to being intracellular ?
o Gain nutrients
o Shielded from host cell
o Easy to reach another vector (Mosquito)
o No MHC antigens for antigen presentation in RBC
260
What are the disadvantages to plasmodium to being intracellular ?
o Parasite must convert terminally-differentiated erythrocytes into cells with nutrient uptake systems
o Remodelling of the cell membrane by the parasite leads to increased cell rigidity
could be removed through the spleen
261
What are apicomplexan parasites ?
Apicomplexan parasites use gliding motility to invade host cells
- Used by motile stages of the lifecycle to migrate to their host cell and actively propel themselves into the host cell
- Substrate-dependent cell motility – does not involve flagella or cilia or shape-shifting
262
What is the survival trade-off of the malaria parasite ?
Malaria parasites adopt a ‘trade of’ strategy between survival and reproduction
- Asexuals and gametocytes
- Maximises transmission opportunities whilst maintaining infection
263
Name an extracellular parasite
human African trypanosoma
264
Advantages to being a extracellular parasite
o Glucose and nutrient-rich environments
o Readily accessible to insect vector
265
disadvantages to being a extracellular parasite
o Exposed to the host immune system
o Proliferative stages cannot survive in the Tsetse fly gut
266
A parasite is covered with ...
variant surface glycoprotein (VSG) coat
267
What is the role of the variant surface glycoprotein (VSG) coat
- Shields the parasite surface by hiding invariant proteins
- N-terminal – antigenic diversity, C-terminal – surface packaging
- VSGs are transcribed from an expression site, one active at a time
268
How do VSG form ?
Gene conversion, segmental gene conversion, telomere exchange, transcriptional switch allows for VSGs
269
How does Trypansomes cause long-term chronic infection ?
- Trypanosomes have an inexhaustible repertoire of antigenic variants, VSG genes undergo high rates of mutations
o Can establish long-term chronic infections
270
Transmission of a parasite requires ...
differentiation
271
slender form proliferation
increase in parasitaemia, increase in concentration of soluble stumpy induction factor (sif), some parasites differentiate into non-replicating, but transmissible, stumpy forms
272
Stumpy form transmission
transmission
273
3 sub-species of Trypanosome brucei
Trypanosoma brucei brucei
Trypanosoma brucei rhodesiense
Trypanosoma brucei gambiense
274
What are the factors dependent on how susceptible a human is to trypansoma brucei ?
- SRA, TgsGP
275
Helminth parasites are ...
Multicellular organisms that can range from millimetres to tens of meters in length
276
Nematodes parasite examples
Ascaris lumbricoides
Onchocerca volvulus
Trichuris trichiura
Wuchereria bancrofti
277
do female or male tsetse flys transmit sleeping sickness ?
both
278
Do female or male mosquitos transmit malaria ?
female only
279
Apicomplexa parasites
Plasmodium falciparum
Cryptosporidium parvum
Toxoplasma gondii
280
Trypansomes respond to SIF to differentiate to short stumpy forms, what does SIF stand for ?
Stumpy induction factor
281
Which is a characteristic of Onchocerca volvulus infection?
river blindness
282
Which parasite forms tissue cysts in the CNS and is a risk during pregnancy?
Toxoplasma gondii
283
Which of the following is a protozoan parasite that causes a deadly amoebic brain infection?
Naegleria fowleri
284
Which of the following parasites has only an extracellular stage in its lifecycle?
Trypanosoma brucei
285
Wuchereria bancrofti causes pathology primarily via
Blockage of lymphatic vessels
286
What kind of pathology is associated with schistosomiasis in the liver?
Fibrosis due to trapped eggs
287
Which statement best describes the variant surface glycoprotein (VSG) coat in Trypanosomes?
It masks underlying invariant antigens
288
Why is immunity against helminths difficult to develop?
They suppress immunity and live for years
289
Plasmodium falciparum causes severe malaria partly because
Infected erythrocytes block small vessels
290
The hygiene hypothesis suggests:
Parasites suppress autoimmune diseases in endemic areas
291
Which parasite is acquired via larval penetration through the skin?
Schistosoma mansoni
292
Naegleria fowleri typically enters the body through:
The nasal passages
293
name an obligate parasite
Ascaris lumbricoides, plasmodium falciparum
294
name a facultative parasite ?
Naegleria fowleri
295
How are parasitic infections marginalised ?
hot and humid area
296
parasitic worm
helminths
297
what is a problem with modernisation of develeoped countries ?
hygiene hypothesis
298
How does roundworm infect ?
Ascaris lumbricoides eggs are ingested then larvae emerge in the duodenum and feed in the intestines and pass out the feaces
299
What are the 2 filarial worms ?
Wucheria bancrofti- lymphatic filariasis
Onchocerca volvulus- river blindness
300
what is the definitive host of taenia solium ?
cows and pigs
301
What causes cysticercosis ?
Taenia solium, lay eggs in the CNS leading to seizures and epilepsy
302
schistosoma spp are trematodes and cause
schistosomiasis - liver fibrosis and CNS difficulties, blood in urine, infertility and gentical ulcers
303
malaria is a ... parasite
protozoan
304
whats the difference between helminths and protozoan parasites
helminths: multicellular worms, animalia, large, complex cycle
protozoan: unicellular, protista, microscopic, binary fission
305
toxoplasma life cycle
intermediate host - any mammal, definitive is cats, transmission through predation, forms cysts that can be ingested in meat or in faeces
306
examples of a kinetoplastid
trypansoma
307
PfEMP1
antigen on erythrocyte when infected with plasmodium falciparum that can lead to thrombosis
308
How are VSG switched ?
gene conversion, segmental gene conversion, telomere exchange, transcriptional switch
309
stumpy inducer factors are released when ...
parasite density in the blood is too high
310
stumpy forms of T. brucei are for ... and slender are for ...
transmission, proliferation
311
fungi kingdom is split into ...
basidiomycetes and ascomycetes
- Branching away from these are chytrids, zygomycetes and glomeromycetes
312
Cellular slime moulds – “social amoebae”
part of protista kingdom and dictyosteliomycota phylum
- Aggregations of amoebae differentiate into spore-bearing fruiting structures
313
Chemotaxis of amoeba
Chemotaxis of amoeba to micro-pipetted cAMP:
- Induction of cellular extensions termed pseudopods that grow in response to a micropipette containing a solution of cyclic AMP
- Actin causes the amoeba to bulge towards cAMP
314
plasmodial slime moulds
single cell containing many nucleus, part of protista kingdom and myxomycota phylum
- Exist as a single wall-less cell (plasmodium) and can contain many thousands of nuclei
315
structures of yeast cells
spindle pole bodies, lipid bodies, bud scars
316
example of budding yeast
Saccharomyces cerevisiae
317
example of fission yeast
Schizosaccharomyces pombe
318
yeast cell cycle
- Start spindle pole body duplication bud emergence nuclear migration and division cytokinesis
319
Yeast classification
fungi kingdom and ascomycota phylum
320
Hyphae
Hypha is used to describe a filamentous fungal cell: a fungal network composed of multiple interconnected hyphae is termed mycelium.
- Only filamentous fungi form hyphae
321
tip growth involves ..
polarised extension in which the increase in cell length is restricted to a narrow region of a few micrometres at the cell tip
322
cells that exhibit tip growth are often ...
- Fungal hyphae
- Pollen tubes
- Root hairs
- Algal and fern rhizoids
- Moss cell filaments
323
most of fungal biomass results from ...
hyphal tip growth
324
what are germ tubes ?
Germ tubes are specialized hyphae which emerge during spore germination and are involved in colony establishment
325
spores can survive extreme conditions like ?
- Certain spores can survive and germinate after extreme conditions (freezing temperatures, Vaccum, electron beam/radiation) and extended time
326
What are septa ?
cross-walls found within hyphae and allow for compartmentalisation – for support and limit movement of organelles
327
hyphae aggregate to form ...
rhizomorphic mycelium
328
rhizomorphic mycelium
thick strands of hyphae which have adhered. Helps the fungus cover area, grow quickly through substrates and establish a feeding network
329
the hyphae have ...
apical vesicle cluster, microtubules, septum, woronin body
330
Spitzenkorper
- Spitzenkörper (apical vesicle cluster) found by phase-contrast microscopy, contain apical vesicles and microvesicles, often contains core region with few vesicles, plays a pivotal role in regulating hyphal tip growth.
- They contain lots of secretary vesicles
- A multi-component organelle assemblage predominated by vesicles
331
What does stress do to Spitzenkorper ?
dichotomous branching and retraction
332
what does osmotic stress of to hyphae ?
bursting
333
septa can ...
become rapidly blocked if hyphae become damaged or eaten by mites
- Some septal pores can also be blocked in old hyphae
334
Characteristics of mitochondria in fungi ?
- energy production
- structure: same as animals
- calcium storage
- distributed throughout fungal hyphae and contained within spores
- interact with other organelles
- highly motile and dynamic
335
Golgi cisternae in fungi
- glycosylation and packaging of proteins into vesicles
- filamentous fungi do not form golgi stacks as observed in animals and plant cells
336
Vacuoles in fungi
- spherical and tubular vacuolar compartments in hyphae
337
Nucleus in fungi
- fungal colony is a supra-cellular interconnecting network of multinucleate hyphae
- they pass through the open septal pores
- more common in the apical hyphal compartments
338
fungal mycelium
the fungal mycelium is composed of a complex, interconnected network of hyphae
- increase in colony diameter via hyphal tip growth
- hyphal fusion and additional growth occur in the colony interior, as the colony matures
Hyphal branches grow towards each other in older parts of the fungal colony
339
Nuclear comets
‘Nuclear comets’ move rapidly through the colony network of Neuorspora crassa
340
endoparasitic fungi
Hirsutella rhossiliensis
341
nematotrophs
parasites of nematode worms
- nematodes are trapped by specialized hyphae and adhesive knobs. Pleurotus ostreatus (Basidiomycota) produces both adhesive traps and “toxic droplets”.
342
steps in insect infection by fungi
Spores land on cuticle germination (appressorium formation) penetration of cuticle (growth within cuticle) invasion of epidermis and hypodermis) tissue invasion by normal hyphae and proliferation of hyphal bodies or yeast-like cells insect death saprotrophic growth dispersal by spores/resting stage
343
What is mycoses ?
moulds which infect humans
- increase with use of immunosuppressant drugs in transplant and cancer therapy, HIV/AIDS
- mainly opportunistic
344
examples of mycoses
dermatophytes, commensals, opportunistic
345
dermatophytes
cause ringworm, athlete’s food, nail infections, example of parasitism
- All dermatophytes are ascomycete fungi and primarily asexual
- Reproduce by asexual spores called conidia – commonly spread infection
- Arthrospores (fragmentation of hyphae) and pigmented hyphae can also spread infection.
346
fungal commensals
grows harmlessly on mucous membranes, but under appropriate conditions can become invasive pathogens, candida albicans
347
opportunistic fungi in the lungs
found normally as saprotrophs, but can grow in the lungs and invade the tissues of immune-compromised individuals
o Sporothrix brasiliensis: opportunistic pathogen of wounds or traumatised tissues e.g., Pneumocystis jirovecii
348
Arthrospores
fragments of hyphae
349
dermatophytes cannot grow at ... and cause ...
- Cannot grow at 37C
- Irritation caused by them allows for skin lesions
- Inoculum flakes of skin in areas, in which the fungi can exist in dormant phase
- The indirect transmission is thought to be more important than direct host-to-host transmission
350
hyphal fronds
flattened ‘hyphal fronds’ can grow in planes of weakness within a stratified substrate such as skin flakes, hair structures act as a perforating organ
351
dermatophytes pathogens are ... as they produce ...
keratinophilic, keratinase
352
candida albicans
Candida albicans is a type of yeast that frows harmlessly as a commensal on mucous membranes of the mouth, gut and vagina. Dimorphic (change from budding yeast to hyphal growth)
- Major fungal pathogen that causes thrush
353
stages of candida albicans
- Yeast hypha (adhesion and colonisation)
- Hypha yeast (epithelial penetration and infiltration into tissues)
- Dissemination within the blood stream
- Yeast hypha (endothelial colonisation and penetration and infiltration into tissues)
354
dimorphic candida albicans
changes between budding and hyphal growth.
low pH and below 30C favours budding
starvation at pH 7 and at 27C favours hypha
355
opportunistic pathogens must ...
Any fungi that produce small spores, smaller than alveoli. Can grow at 37C, can withstand/evade host defences.
356
examples of opportunistic fungi
- Aspergillus fumigates invade the lung through the alveoli from the spores.
- Cryptococcus neoformans infects the CNS cuasing meningitis and cryptococcosis, produces basidiospores (sexual spores of basdiomycota)
357
basidomycetes fungus produce ...
basidiospores
358
basidiomycetes fungus
exist as a yeast in host and spends most of its life growing as a yeast. Pathogenicity factors: ability to grow at human body temperatures, growing in presence of 5% CO2. Capsule of polysaccharide, melanin protects from UV radiation and oxidants
359
main fungal treatments
azoles inhibits ergosterol synthesis for the membrane, polyene antibiotics forms pores disrupting ion homeostasis , echinocandins inhibits synthesis of beta glucans for the cell wall , flucytosine inhibits DNA and protein synthesis
360
uses of fungi
fungal textiles uses chitin rather than cellulose, medical products like freeze dried pads for absorbents, pencillium can be grown from the mold on citrus fruits
361
Aflatoxin
carcinogenic toxin produced by aspergillus flavus
362
Coprine
produced by ink caps and cause toxic symptoms when consumed with alcohol
363
Muscimol and Muscarine
allow by pass of blood brain barrier
364
Orellanin
a toxin produced which affects the kidneys
365
Amanitins
nausea and vomiting leading to liver damage and deaths
366
Psilocybin
indole alkaloids can cause heightened perceptions, euphoria, paranio and hallucinations
367
Clavices purpura (ascomycota)
produces sclerotia which is a cocktail of alkaloids that harm rye and grasses but also have vasoconstrictive and pschyoactive effects
- Sporocarps grow from a sclerotium which has survived dormant in the soil for several months
368
ergot alkaloids
derived from LSD (made from fungus), from these have helped with migraine symptoms
369
Woronin body
specialized organelles found in the filamentous fungi of the Pezizomycotina class, serving as a defense mechanism by plugging septal pores to prevent cytoplasmic loss during hyphal damage
370
what fungus is this descrbing: The presence of a polysaccharide capsule, the ability to grow at 37° Celsius and in high levels of CO2 are important features that affect its pathogenicity
Cryptococcus neoformans
371
Fluconazole
Inhibits ergosterol synthesis
372
5-Flucytosine
Inhibits DNA and protein synthesis
373
Caspofungin
Inhibits β(1-3)-glucan synthesis
374
Amphotericin B
Forms pores in the plasma membrane
375
Which of the following is true of fungal mitochondria?
Interact with other organelles and are dynamic
376
Which of the following is not involved in tip growth?
A. Pollen tubes
B. Fungal hyphae
C. Yeast buds
D. Moss cell filaments
yeast buds
377
Germ tubes emerge during...
spore germination
378
The apical vesicle cluster known as the Spitzenkörper is best observed using:
Phase-contrast microscopy
379
Which antifungal drug targets β-1,3-glucan synthesis in fungal cell walls?
Caspofungin
380
Which of the following contributes to Cryptococcus neoformans virulence?
Melanin production
381
Which fungal pathogen is most associated with opportunistic infections in immunocompromised individuals?
Aspergillus fumigatus
382
Which of these is not a function of the fungal vacuole?
A. Calcium storage
B. Protein folding
C. Degradation
D. Turgor pressure regulation
Protein folding
383
Which of these is not a known use of fungi in biotechnology?
A. Enzyme production
B. Vaccine development
C. Ethanol production
D. Antiviral drug synthesis
antiviral drug synthesis
384
Which class of antifungals binds directly to ergosterol in fungal membranes?
Polyenes
385
Which of the following is true of chytrids?
They form complex fruiting bodies
386
What are the 4 methods of switching between VSGs in Trypansoma brucei ?
gene conversion, segmental gene conversion, telomere exchange, transcriptional switch
387
