Viral properties L9 Flashcards
3 shape variations of viruses
Icosahedral
filamentous
spherical
icosahedral=
highly symmetric 20 faces
self-assembles
3 significant features of viruses
- Obligate intracellular parasite
- Depend on biochemistry machinery of host cell to replicate
- replication is by assembly of individual components
what is the nucleocapsid
the genome contained within a protein capsule
virion=
the infective viral particle
for non-enveloped viruses (naked)=
nucleocapsid= virus particle= virion
for enveloped viruses =
virion= nucleocapsid + envelope
what often protrudes from the surface of the virus particle and are involved in contact with the host cell
protein or glycoprotein structures called spikes
what can the enveloped be made from
derived from the host membrane via budding
e.g of enveloped virus
influenza
spikes on influenza (2)
- H
- N
H spike=
hemagglutinin receptor recognition on host cell (specificity
N spike=
neuramindase
what are H and N susceptible to (2)
- antigenic drift (mutations)
- Shift (recombinations)
e.g of a naked virus
norovirus
3 advantages of being non-enveloped
- more stable in face of environmental spread (no phospholipid membrane
- spreads more easily
- Survives gut, poor water treatment ect
4 consequences about enveloped viruses
must stay wet to remain infectious
very sensitive to detergents
spreads through large droplets
does not need to kill cell to spread (buds)
e.g 3 enveloped viruses
HIV
Ebola
Influenza
what is the key way of classifying viruses
Nature of the genome
transcription=
making a + strand mRNA from DNA
what is negative mRNA
the complementary strand
translation=
proteins from mRNA
always needs positive stranded mRNA
2 tasks to make new virus particles
- make mRNA to be translated to make new viral proteins
2. Make nucleic acids; copies of own genome to be packaged
3 classes of protein viral genome codes for
- proteins for progeny viral particles
- Enzymes for genome replication
- Proteins to interfere with host immune defence
do humans have negative RNA
no
3 classification of viruses on genome
RNA
DNA
retrovirus
retrovirus=
contain reverse transcriptase
have RNA to DNA step in life cycle
6 stages of the infectious cycle
- attachment
- penetration
- uncoating
- replication (gene expression)
- assembly
- release
burst size=
yield of infectious virus/cell
time required for single cell of virus to reproduce
Negative ss RNA are all ______
enveloped
entire life cycle is normally extra nuclear (3)
Negative ss RNA
Positive ss RNA
positive ds RNA
in neg ss RNA how are progeny viruses released
budding
life cycle of Retrovirus (e.g HIV)
- RT enzyme
- viral genome integrates into host cell chromosomal DNA
- viruses are packaged in cytoplasm and released by budding
where are DNA viruses usually assembled
in the nucleus and released by cell lysis
why very few antivirals?
limited choice of targets for anti-viral drugs
what is it called when viral infection causes death of host cell
lytic infection
what happens when genomic material is retained in host cells
latent infection
slow release of viral particles may lead to
persistant infection
how can viruses cause tumour cells
virus might induce transformation of the host cell leading to formation of normal cells to tumour cells
what can be viral oncogenes (4)
regulatory factors
receptor molecules for growth factors
signalling molecules
transcription factors
2 ways oncogenes can occur
- introduction of oncogenes
2. insertion of viral DNA into host genome activates host cellular oncogenes
shape of rotavirus
icosahedral
shape of ebola
filamentous
shape of adenovirus
spherical
name 4 negative SS RNA viruses
influenza,
mumps and measles
rabies
ebola
name 3 positive SS/ds RNA viruses
poliovirus
dengue
hepatitis C
name 2 DNA viruses
herpes, Epstein barr virus (EBV)
name a retrovirus
HIV
