Viruses Flashcards
What are Viruses ?
Infectious agents that require a host in order to replicate
What do ‘obligate parasites’ lack ?
The mechanism for metabolic energy/protein synthesis
How are viruses classified ?
1) By morphology
2) Chemical composition
3) Mode of replication
What are virons (virus particles) assembled from ?
They’re assembled from pre-formed components
Name the pre-formed components virons are assembled from ?
1) Genome - which contains either DNA or RNA
2) Protein shell (Capsid) - together w/genome = Nucleocapsid
3) Membrane envelope
4) Outer layer (for protection and for recognition sites of host cells)
Give an example of a ‘non-serious’ virus and the infection it causes
- Rhinovirus - causes a cold
Give an example of ‘serious’ viruses
- Enteroviruses
Give examples of sever diseases caused by viruses
1) Rabies
2) Ebola
What is the importance of the Capsid of a virus ?
It allows for classification of a virus
Name 3 classes of Viruses ?
1) Helical
2) Icosahedral (formed by capsomers)
3) Complex
What is meant by a Naked virus ?
Virus that has a capsid only and no envelope
What is meant by an Enveloped virus and what is the envelope made out of ?
The capsid is surrounded by an envelope which is made out of Lipids and proteins
Name an example of complex virus
bacteriophage T4
Give 3 functions of the the Capsid
1) Protection -from the hosts acid and from protein-digesting enzymes
2) Assists in binding and penetrating host cell
3) Stimulates the host’s immune system
The nucleocapsid of an enveloped virus is more flexible than that of a naked virus. TRUE or FALSE ?
TRUE
Envelope spikes (glycoproteins) consist of carbohydates and protein complexes which are used in attachment to host cell. TRUE or FALSE ?
TRUE
Virus DNA or RNA can be double (ds) or single stranded (ss). TRUE or FALSE ?
TRUE
ssRNA further divides into Positive and Negative polarity. TRUE or FALSE ?
TRUE
DNA viruses fall into class 1, 2 AND 7. TRUE or FALSE ?
TRUE
RNA viruses fall into class 3-6. TRUE or FALSE ?
TRUE
RNA viruses show very rapid rates of mutation. TRUE or FALSE ? and why ?
TRUE, because they DO NOT have proof-reading abilties
DNA polymerases possess proof reading abilities, therefore less mutations and evolve less rapidly. TRUE or FALSE ?
TRUE
Give 2 mechanisms Viruses may use to evade detection ?
1) Change their antigens, therefore they’re not recognised
2) Generalised immune response
How many stages of the Viral cycle are there ? Name them.
6
1) Attachment
2) Penetration
3) Uncoating
4) Genome replication
5) Assembly of virion particle
6) Release
Many viral infections are not silent. TRUE OR FALSE?
FALSE
What does the outer layer of a virus do?
It provides protection and it is the recognition site for host cells
How are viruses classified?
By morphology and chemical composition/mode of replication
The capsomere does not forms the main building blocks of isohedral structure. TRUE OR FALSE?
FALSE
Icosahedral virus can be enveloped (with a capsid) or naked (without a capsid). TRUE OR FALSE?
TRUE
Give an example of a non enveloped icosahedral virus?
Adenovirus
Helical viruses can be enveloped or naked. TRUE OR FALSE?
TRUE
What does a helical virus assemble into together with viral nucleic acid?
Helical structure
Give an example of a non enveloped and non enveloped helical virus?
non -Ebola
Influenza is enveloped
What are complex viruses made up of?
Repeated units of a single polypeptide protomer
What structures does Complex viruses together with nucleic acid form?
Helical structure
What is enveloped spike involved in?
Recognition and attachment
What are the mechanism that viruses used to avoid detection?
- Changing their antigens, so not recognised
2. Generalises immune suppression
What does reverse transcriptase produce?
It uses a single stranded RNA genome to create a double stranded DNA
Reverse transcriptase , involves DNA to RNA. TRUE OR FALSE?
TRUE
What occurs during the initial contact of a viral infection?
Glycoproteins on the surface bind to cell surface
What are the two different phases during initial contact of viral infection?
Reversible phase - electrostatic repulsion reduced
Irreversible phase - initiation of viral penetration
What two mechanisms are initiated during the conformational changes of the anti-receptor - receptor complex?
Endocytosis (cell membrane is engulfs virus)
Fusion of viral envelopes and cell membrane (releases capsid into cytosol)
What are the two main routes of virion release?
Lysis
Budding
How are enveloped and non enveloped viruses released?
Enveloped - By budding
Non enveloped - By lysis
What does Hepatitis cause?
Inflammation of the liver
Hepatitis A - highly contagious, contamination is via water, it is a mild infection and can be self resolving. TRUE OR FALSE?
TRUE
Hepatitis B and C does not spread through body fluid and can cause long term disease. TRUE or FALSE?
FALSE
HBV is a small DNA virus that replicates through an RNA intermediate and can integrated into host genome. TRUE OR FALSE?
TRUE
The synthesis of influenza mRNAs and replication occurs in the nucleus. TRUE OR FALSE?
TRUE
For normal RNA viruses where does replication and synthesis occur?
In the cytoplasm
What are the two subtypes that influenza A is divided into?
Hemagglutin (H)
Neuraminidase (N)
What are the stages of HIV?
Acute infection - HIV replicates rapidly, CD4 count drops
Clinical latency - Virus replication much slower/immune system becomes compromised due to low CD4 count
AIDS - acquired immunodeficiency syndrome / immune system severely compromised / vulnerable to infections and infection related cancers.
Some viruses induce (bring about) cancer. TRUE OR FALSE?
TRUE
Give an example of an antiviral therapy
Vaccination
