Biological Agents as cause of disease Flashcards Preview

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Flashcards in Biological Agents as cause of disease Deck (31):

What are obligate pathogens?

Can only survive in host, usually very specific to host species


What are facultive pathogens

Present in the environment waiting for host


What are opportunistic pathogens?

Secondary pathogens, normally benign but cause disease in compromised host


What are virulence genes?

Gene that makes a species able to cause disease
- Clustered on pathogenicity islands
- Can be carried on bacteriophages that incorporate into bacterial DNA


What is dimorphism?

The ability to have two different forms - fungal pathogens show it


What is a vector?

An insect that transmits a disease


What are the protective barriers against agents of disease?

Epithelia - tight junctions


What is pertussis toxin?

Interferes with the chemotactic pathway of neutrophils which destroy bacteria


How does E.coli make the host secure them?

Using a type III secretin system, make the host cell create an actin pedestal


What is Legionnaire's disease?

Caused by a bacterium that normally infects amoebae, Legionella pneumophilia
- If inhaled, L.pneumophilia is phagocytosed
- It then replicates inside the macrophages


How does L.monocytogenes avoid destruction in cells?

Secretes listeriolysin O, protein that breaks down membrane of phagosome
- Only works when pH acidic
- Degraded in cytoplasm as pH too high for them to work
- L.monocytogenes replicate in host cell


How does L.monocytogenes induce actin polymerisation?

- Used to move into new cells
- Assemble actin tails that push them into neighbouring cells
- Bacterial protein, ActA, initiates actin polymerisation at tail end


How do antibiotics work?

- Stop bacterial growth by disrupting cellular processes
- Majority based on natural products produced by fungi or bacteria


What is a single virus particle called?



What are viruses?

Encode a small number of proteins, encased in a coat protein called a capsid
Capsid further coated in envelope virus


How/when does a virus exit a cell?

- Virus enters cell and is broken into compartments
- Can be transcribed to form RNA or replicate to make DNA
- Then translated to form proteins
- DNA replicated, protein can be assembled to form virion
- Exits cell - if enveloped, leaves by budding, or a simple virus has to kill the cell


How are viruses classed?

Genome type and how their mRNA (+strand) is made
- Baltimore Classification


What is Class I?

Most similar to normal cells, one molecule of dsDNA
- Adenoviruses: respiratory, conjunctivitis
- SV40
- Herpes
- Papilloma


What is Class II?

Small, one molecule of ssDNA
- Parvoviruses - fifth disease


What is Class III?

Segmented genomes, 10-12 molecules of dsRNA
- Rotavirus (acute astroenteritis)


What is Class IV?

RNA infectious by itself, single positive strand RNA
- Polio viruses
- Toga viruses: yellow fever


What is Class V?

The virion carries RNA transcriptase, single minus strand RNA
- "RNA dependent RNA polymerase"
- Ebola virus, influenza
- Paramyxoviruses: measles


What is Class VI?

Retroviruses that form dsDNA form a positive strand plus a reverse transcriptase, ENVELOPED
- Human T-cell lymphotrophic viruses
- Human immunodeficiency viruses


What is Class VII?

Double stranded DNA and reverse transcriptase
- DNA made into genomic RNA
- Hep B


What strand is used as the template strand?

+ strand


What are the different entry strategies for viruses?

1) RNA enveloped virus
- Can fuse with host's membrane
- Uses receptors

2) Endocytosis (influenza)
- Envelope taken up into the membrane
- Virus has second membrane around it (endocytic vesicle)
- Vesicle can be acidifies - causes envelope mem to fuse with vesicle mem, removes coat and allows RNA into cell

3) Endocytosis (non-enveloped)
- Can't fuse with vesicle membrane
- Creates its own pore that lets contents come out

4) DNA virus - endocytosis
- Once endocytosed, ets into endocytic vesicle
- Forms early endosome
- Fully breaks open endosome and lyses membrane
- Needs to get into nucleus


What are E6 and E7?

Oncogenes in the papillomaviruses virus - normally act by turnin up hosts DNA replication machinery to make more virus


How is upregulated cell proliferation caused from transformation?

Transformation results when viral genome integrated into hosts genome and malfunctions - too much E6 and E7 produced
- Leads to unregulated cell proliferation


What do E6 and E7 do?

Take the breaks off host cell proliferation
- Bind the host proteins Rb an p53 to inactivate them - releasing constraints on DNA repl


How can retroviruses cause cancer?

- Carry an oncogene
- Incorporating human proto-oncogenes into their genome
- Thought to occur when mistakes made during integration of viral genome into host


How are proto-oncogenes involved with cell proliferation?

- c-src is a kinase that is a powerful activator of cell proliferation
- Normally, cell down regulates c-src activity by phosphorylating one end of the protein (a)
- This causes the protein to fold on itself to become inactive
- v-src (viral form) does not have the c-terminus, creating an oncogenic form of src