Virology I & II Flashcards
Name some viral diseases present in humans
In humans there is a wide range of viral diseases e.g. - cancer - immunodeficiency - respiratory these can be acute or chronic
What are the different structures of viral genomes?
ssRNA - single stranded RNA
dsRNA - double stranded RNA
ssDNA - single stranded DNA
dsDNA - double stranded DNA
Double stranded genomes have complementary base pairings
RNA genomes are linear or circular
Genomes can encode info in positive or negative 5’-3’ or 3’-5’ directions
Name some examples of HIV associated pathogens
Virus - KSHV or HSV
Bacteria - mycobacterium & salmonella
Parasites - Toxoplasma gandii
Fungi - Candida
Use the central dogma to explain how virus’ form proteins in the host cell
- DNA replication via DNA polymerase (DNA -> DNA)
- Transcription occurs via RNA Polymerase (DNA ->
mRNA) - Translation of proteins via ribosomes (mRNA -> protein)
What are the 2 types of way a virus can cause disease?
Directly - as a product of their host range & tissue tropism
Indirectly - by promoting/inhibiting cell functions
Which structural proteins are present in viruses?
Capsids formed by proteins have viral nucleic acids packaged into it
Proteins interact with one another in protein-protein interactions
What is the role of polymerases?
Polymerase proteins catalyse nucleotides into nucleic acids
DNA viral genomes produce DNA Polymerases
RNA viral genomes produce RNA Polymerases
Polymerase proteins interact with specific nucleic acids in proteins-nucleic acid
interactions
Outline how viral replication occurs
- Entry into cell
- attachment/entry through glycoprotein on virus with
receptors on host cell via direct fusion or endocytosis - Genome movement within cell where most
advantageous nucleotides found- intracellular structures used to synthesise viral DNA
- Genome replication
- Genome packaging into protein shells encoded by new
viral DNA- packaging sequences in viral DNA/RNA
- Exit from cell
- budding or lysis
How can viruses cause cancer?
As cells divide in cell cycle, nucleotides are produced that can be used by viral polymerases to form new viral genomes
Some viruses can produce proteins ensuring continuous cell cycle - uncontrollable cell division
~ 30% cancer caused by viruses
What is pathogenesis?
When viral and cellular proteins shape the intracellular environment to facilitate viral replication and evasion of the immune response which leads to disease
What is meant by a chronic disease?
A persistent or life-long disease (typically anything > 3 months
Give examples of viral infections and how they’re transmitted
Respiratory viral infections:
- Adenovirus / Influenza
- replicate in lungs
- transmitted by air via coughing, sneezing, breathing etc.
Genital infections:
- replicate in procreation tissues
- transmitted via sexual intercourse
Immunodeficiency Virus’
- replicate in immunity cells
- prevent immune function
- indirect infection
some choose not to replicate immediately and so cannot be detected by the immune system
How do HIV cause T cell death?
Causes apoptosis of immature thymocytes induced by death receptors and activation-induced cell death
HIV inhibits immune cell function resulting in patients being open to attack from any infectious bacteria or virus causing diseases
What is an acute disease?
Disease that are severe and sudden in onset - are typically resolved quickly
How is it beneficial for virus’ to replicate within host cells?
Host cells contain nucleotides that virus’ can use to produce their own viral DNA
Virus’ also use these nucletoides to encode proteins for their protein coat in which the newly synthesised viral DNA is packaged. Protein formation cannot occur outside a cell, therefore replication within host cells is beneficial for this purpose also
What is the significance of viral structures?
Different viruses have different structures, but retain similar organisations
Virus structure can dictate host range and tissue tropism
What is a virus’ host range?
The spectrum of cells a virus can infect and lyse
What is endocytosis?
Cellular process when a virus is brought in by invagination of its membrane to form a vacuole
Give examples of some oncogenic viruses
HPV - human papilloma virus EBV - epstein-Barr virus HBV - hepatitis B virus HCV - Heoatitis C virus HIV - human immunodeficiency virus HHV8 - human herpes virus 8 HTLV-1 - human T-lymphotropic virus MCV - merkel cell polyomavirus
Where are viruses found?
Viruses can be found in different hosts e.g.
- Humans
- Plants
- Animals (& insects)
- Bacteria
Some viruses can move between hosts
Describe the structure of a bacterium
Contain nucleic acid (DNA) covered in protein
Have a cell wall - coat of sugar molecules
Can replicate outside of cell
Describe the features of a virus
Nucleic acids (DNA/RNA) covered by protein coat
Don’t contain cell wall
Can have a lipid coat
Replicate inside host cells
How do virus’ enter a cell via direct fusion?
Virus’ with viral envelopes containing receptors attach to cell surface receptors causing secondary receptors to puncture/fuse the cell membrane allowing viral entry into the cell
How many types of virus are there?
We don’t know how many different types of viruses there are in each host as new viruses are constantly being found
How does HPV cause cancer?
HPV proteins E6 and E7 remove molecular switches in the cell cycle
E6 influences master regulater gene P53 (damaged DNA can still undergo cell cycle) which regulates P21 and cyclin A function
E7 protein binds directly to RB affecting proteins E2F in cell cycle
These cause cell cycle checkpoints to no longer be effective
What is meant by tissue tropism in regards of a virus?
Cells and tissues of a host that can support the growth of a particular virus.
Some virus’ have a broad tissue tropism; can infect a large variety of cells & tissues of a host
How do viruses cause immunodeficiency?
Viruses must evade immune responses
They achieve this by replicating within immune cells, hiding virus from immune cells therefore depleting cell function
Inhibition of immune cells allows other pathogens to replicate in infected hosts
=> causing disease
Outline how virus’ form DNA genomes using the central dogma theory
DNA replication occurs via DNA polymerase (DNA -> DNA0
How do viruses cause disease?
Viruses evolve to replicate in tissues favouring transmission between hosts, allowing them to evade the host’s immune system
How are RNA viral genomes produced by the virus?
If positive sense RNA present (5’-3’)
replicate using RNA polymerase
translate RNA into protein via ribosomes
If negative sense RNA (3’-5’)
viral enzyme RNA dependent RNA polymerase converts -ve into +ve RNA
replicate using RNA polymerase
translate RNA into protein via ribosomes
Describe the key features of Prions
Don’t contain nucleic acids
Replicate inside cells
What is a virus?
An infective agent, typically consisting of a nucleic acid molecule surrounded by a protein coat
What is the Baltimore classification system?
Virus classification system grouping viruses into families depending on their genome and replication method
What is the role of reverse transcriptase?
An enzyme found in retrovirus’ used to generate cDNA from an RNA template
- process is called reverse transcription
What are prions?
Misfolded proteins causing neurodegenrative diseases
