A virus is a [blank_start]nucleic[blank_end] acid surrounded by a [blank_start]protective[blank_end] protein coat ([blank_start]capsid[blank_end]). Replication is dependent on a host cell, viruses can't replicate on their own so are [blank_start]obligate parasites[blank_end].
CYCLE- they are introduced in the popn, they [blank_start]spread[blank_end], they [blank_start]escape[blank_end] cell defences. Some do this by: [blank_start]changing[blank_end] quickly to escape being recognised by the immune system, some have safe ways to escape, some aren't good at escape but can replicate and infect [blank_start]very easily[blank_end] so the immune system has [blank_start]no time[blank_end] to respond to them.
They cause disease and attract publicity. HIV is one of the biggest killers, but not always lethal.
TYPES of virus:
ds DNA, ssDNA, dsRNA, ssRNA and retrovirus ([blank_start]RNA[blank_end] virus with [blank_start]DNA[blank_end] intermediate)
Viruses have [blank_start]intracellular[blank_end] and extracellular ([blank_start]virion[blank_end]) phases. Virions are much smaller than other life forms.
Nucleic acid surrounded by protective protein [blank_start]capsid[blank_end]. The capsid is a distinctive feature. It's very repetitive. Some virions are surrounded by a membrane= [blank_start]enveloped[blank_end] virus, with no membrane= [blank_start]naked[blank_end]
The capsid is made of [blank_start]capsomers[blank_end]. [blank_start]Nucleocapsid[blank_end]= nucleic acid+capsid.
Attachment to target cells is mediated by [blank_start]proteins[blank_end] or spikes on viral surface which bind to host surface molecules. often [blank_start]glycoproteins[blank_end]. these are viral receptors.
1) [blank_start]MEMBRANE[blank_end] FUSION. [blank_start]spikes[blank_end] of virion attach to host cell [blank_start]receptors[blank_end] (adsorption), the envelope of the virion then fuses with the plasma membrane. This releases the [blank_start]nucleocapsid[blank_end] into the cytoplasm, the viral envelope [blank_start]remains[blank_end] part of the plasma membrane. The nucleic acid then [blank_start]separates[blank_end] from the [blank_start]capsid[blank_end] coat protein.
2) [blank_start]ENDOCYTOSIS[blank_end]. Virion adsorbs to hot cell, endocytosis. Plasma membrane surrounds the vision and a [blank_start]vesicle[blank_end] forms. This also occurs for [blank_start]naked[blank_end] viruses.
DNA viruses MUST GO to [blank_start]the NUCLEUS[blank_end] as they need transcription-->Viral DNA is transported to the [blank_start]host[blank_end] nucleus-->Host [blank_start]RNA polymerase[blank_end] converts DNA to viral [blank_start]mRNA[blank_end] in the nucleus this then is transported to [blank_start]the cytoplasm[blank_end]-->Viral RNAs are translated to new viral proteins and transported back to the [blank_start]nucleus[blank_end]-->Viral DNA gets replicated by [blank_start]DNA poly[blank_end]--> reassembly of viral genome and proteins followed by [blank_start]release[blank_end]
Viral RNA translated to proteins by [blank_start]cytoplasmic ribosomes[blank_end]. Viral [blank_start]RNA genome[blank_end] is replicated by [blank_start]viral synthetase[blank_end]. Viral proteins form the [blank_start]capsid[blank_end] and encapsulate replicated RNA genomes to form new [blank_start]virions[blank_end]. New virions then bud from the infected cell.
Viral proteins which are to become [blank_start]spikes[blank_end] attach to the plasma membrane. Viral [blank_start]matrix[blank_end] protein coats the inside of the membrane. Nucleocapsids become enclosed by viral envelope composed of host plasma membrane. = [blank_start]BUDDING[blank_end]
Viral infections can cause: tumour, cell lysis, persistent infection or latent infection
ds DNA virus, starts as [blank_start]respiratory[blank_end] infection with a high mortality but lead to high immunity. Edward Jenner created vaccination with cowpox but this later changed to vaccinia virus. It was eradicated because it was: [blank_start]exclusive to humans[blank_end], [blank_start]no hidden[blank_end] carriers, 100% vaccine success, only [blank_start]1 serotype[blank_end].
exclusive to humans
only exhibited in humans and cows
not exclusive to humans
only a few
Viruses can change. They infect, immunity ensues, then they change [blank_start]mutate[blank_end] and evolve. There are [blank_start]8[blank_end] types of herpesvirus, alpha beta and gamma, and they are sDNA viruses with large genomes. Infections are lifelong. They undergo a [blank_start]LATENT[blank_end] cycle where few viral proteins are expressed and no virions are produced. They can be activated to express a [blank_start]lytic[blank_end] cycle where all viral proteins are expressed and virions are produced to infect new cells.
Herpes simplex. [blank_start]Cold sores[blank_end]. Infects [blank_start]neurones[blank_end] and manifests as cold sores. If they aren't present then the virus is latent and reactivates due to [blank_start]stress[blank_end].
Poliovirus is a +ve strand ss[blank_start]DNA[blank_end] virus with a linear genome. [blank_start]icosahedral[blank_end] structure. Virion has 4 proteins. vpg protein at 5' end and polyA tail at 3' end.
RNA acts as mRNA and is translated by [blank_start]host[blank_end] ribosomes. A large [blank_start]polyprotein[blank_end] is cleaved to produced 20 proteins. RNA [blank_start]poly[blank_end] transcribes viral RNA to negative RNA strand. This acts as a template for a new +ve RNA strand.
Poliomyelitis- [blank_start]oral[blank_end] infection, infects [blank_start]gut[blank_end] before [blank_start]blood[blank_end]. Targets nerve cells and destroys them, causing [blank_start]paralysis[blank_end] of infected tissues. It develops very quickly so there are no long term asymptomatic carriers, No [blank_start]non primate[blank_end] reservoir in nature.
POLIOMYELITIS. [blank_start]Inactivated[blank_end]- treated with formaldehyde, prevents entry to nerve cells but gut infection remains.
effective, can be incorporated into [blank_start]routine[blank_end] vaccines, good [blank_start]stability[blank_end] in transport and storage, no risk of poliomyelitis in recipients and contacts.
Doesn't introduce local gut immunity, [blank_start]booster[blank_end] vaccines are needed admin by [blank_start]injections[blank_end], higher community vaccination levels needed
[blank_start]Attenuated[blank_end]: cell culture, introduces immunity in the gut and prevents infection
Effective, [blank_start]lifelong[blank_end], similar imm response to natural infection, [blank_start]indirect[blank_end] community immunisation by spread of attenuated virus, oral, no booster needed.
Induced poliomyelitis, spread without [blank_start]consent[blank_end] and unsafe for immunocompromised ppl
Influenza A B and C. -ve [blank_start]ssRNA[blank_end] virus. Killed 20-40 mil in 1918. [blank_start]Segmented[blank_end] genome with 8 segments to produce [blank_start]8 proteins[blank_end]. Helical nucleoprotein. No defined shape, enveloped. [blank_start]Hemagglutinin[blank_end] (HA) attaches to host receptors. [blank_start]Neuraminidase[blank_end] (NA) breaks down sialic acid to allow budding.
1) taken up by [blank_start]endocytosis[blank_end]
2)RNA -ve strand converted to mRNA by viral RNA polymerase.
3)mRNA translated in cytoplasm to make [blank_start]viral[blank_end] proteins.
Antigenic drift-[blank_start]minor[blank_end] mutation. Occurs as a result of activity of viral [blank_start]polymerase[blank_end].
Antigenic [blank_start]shift[blank_end]-[blank_start]major[blank_end] reassortment and strong change, viruses infective different [blank_start]species[blank_end] can recombine in a permissive host leading to major genomic changes.
made of killed vaccine of 3 strains
made of live vaccine
given to most vulnerable
given to everyone
recombinant HA vaccine
Target [blank_start]M2[blank_end] protein to stop viral [blank_start]uncoating[blank_end] in the cell e.g. amantidine. Target [blank_start]neuraminidase[blank_end] to stop viral budding e.g. tamiflu.
Many flu viruses in birds and pigs. Can spread to other animals. Usually not human to human. Serious concerns that antigenic drift or shift would result in human to human transmission.
[blank_start]HSN1[blank_end] Avian influenza infects deep alveolar cells in lungs, causes a strong response called a [blank_start]cytokine storm[blank_end] where a person's own organs are attacked.