Virus structure, viral replication cycle & prions Flashcards
1
Q
Viruses
A
- Viruses infect all living things
- Once infected with those viruses, it is for life
- We carry viral genomes as part of our own genetic material
2
Q
Virus general characteristics
A
- Acellular Infectious particles
- viruses are the smallest infectious agents - don’t need nutrient
- Do not grow or undergo division outside a cell
- Obligatory intracellular parasites requires host for replication
- Assembly of pre-formed viral components such as DNA and RNA
3
Q
Treatment for viruses
A
- Cannot be treated with antibiotics with antiviral agents
4
Q
Virus taxonomy
A
- Viridae - genus
- Virus - species
5
Q
Virus composition
Nucleic acid
A
- DNA or RNA can be single or double-stranded matrix proteins or enzymes
6
Q
Viral compostition
Capsid
A
Protein coat/shell to protect the
nucleic acid
7
Q
Virus composition
Envelope
A
- Lipid bilayer membrane on some viruses, in which
some peripherical glycoproteins (e.g.
Spikes) projects from outer surface
8
Q
Absence envelope
A
- External layer of a virion
- Not always present
- Not present in rhinoviruses, adenoviruses
- Whereas influenza has envelope
9
Q
Envelope
A
- External to viron
- A lipid bilayer derived from host cell
- Acquired by budding of capsid when
viruses leaves the cell
10
Q
Envelope glycoproteins
A
- Transmembrane glycoproteins synthesised through the secretory pathway destined to the plasma membrane
11
Q
Mechanism of Envelope glycoproteins
A
- Involved in binding specific protein receptors on the external surface of the host’s cell (viral absorption, the first step)
12
Q
Capsid
A
- Large and protective shell that surrounds/protects viral nucleic acid
- Composed of many capsomers
- Has identical and reversible bonding contacts with its neighbours
13
Q
Capsid shape
Helical
A
- Capsomere subunit forms a capsid in hollow circular shape
14
Q
Capsid shape
Polyhedral
A
- Many-sided shape 3-D structure
15
Q
Viral genomes
A
- Either DNA or RNA which is double or single stranded
- Encodes for the structure of the virion and invading the host cells and hijacking/regulating its metabolic activity to produce more viral proteins
- Enzymes to reproduce/multiply their genomes
16
Q
Spectrum of a viral infection
A
- Mainly determined by the presence of specific receptors on the surface
- Cells should have cellular factors capable
of replicating virus - Different viruses can bind the same receptor
- Viruses of the same family may bind different receptors
17
Q
Viral replication cycle
A
- Attach to the target of the epithelial cell
- Cell engulfs the virus by endocytosis
- Viral contents are then released
- Viral RNA enters the nucleus which is replicated by the viral RNA polymerase
- Protien synthesis them protien maturation and viron assembly
- Release new viral particle into extracellular fluid not killed in the process
18
Q
Viral attachment
A
- Virus adheres to cell surface with no specificity
- Specific receptors on cell surface by envelope
glycoprotein or protruding capsid protein
19
Q
Virus penetration
A
- By fusion of viral envolope and host cell membrane
mediated by viral fusion proteins if envalope is present - Coreceptor binding induces exposure of the gp41 fusion peptide, which inserts itself into the host cell membrane
- Tethers the viral and host membranes and promotes their fusion
20
Q
Naked virus penatration
A
- Enter cell via endocytosis
- Receptor binding triggers the process of endocytosis
- Cell membrane is pinched off
- The virus is engulfed
- A vesicle is formed
21
Q
Virion uncoating
A
Disassembly of the virion to release the genetic
material in the nucleus of the cell
22
Q
Virus genome replication and protein synthesis
A
- Viruses hijack the host cell synthesis machinery to:
- Replicate their genome
- Produce their proteins
23
Q
Assembly of NEW virions
A
- Many capsid subunits are synthesised via endomembranous system, envelope glycoproteins are synthesised by the cell and sent to the plasma membrane
- Capsid subunits assembled together to form a capsid
24
Q
Release of new virions
Exocytosis/Budding
A
- Completed viral particles exit the cell and can infect other cells
- Enveloped viruses new capsid particles bind the membrane
- The membrane pinches off and viruses acquire the envelope and there are released. Cells are not destroyed
25
# Release of new virions
Lysis – Naked viruses
Viruses are released only when the cell dies
26
Prions
- Don't contain nucleic acids causes transmissible spongiform encephalophaties
- May cause fatal neurological diseases
27
Spongiform encephalopathies
- Long incubation periods
- Impairment of brain function
- Mental and physical abilities rapidly deteriorate
- Always fatal
- Many tiny holes appear in the cortex causing it to appear like a sponge
28
Defence against pirons
- Extremely resistant to standard sterilization techniques cannot autoclave at 121
- Requirement to autoclave at 134 degrees
