Microbiologi 4

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• Virus VS virion The virus refers to the entire virus which is an obligatory parasitic infectious particle and a virion is the infectious particle
• Why is a virus an obligate intracellular parasite. It needs an host cell to replicate and rely on the host for energy, metabolic intermediates and protein sythesis
• Capsid A protein shell that surrounds the genome of a particle. It is made up of capsomeres and they can be in different shapes. Icosahedral=spherical. Helical viruses= rods. Complex viruses= several part. An example is T4 bacteriophage
• Viral envelope It is the outer most layer of many types of viruses and it consists of a phospholipid bilayer. The virus gets this during the release state.
• Spikes Viral protein embedded in the envelope. Glycoprotein projections found on the surface of the viruses
• Process of viral replication 1. Attachment of the virion to the host cell. 2. Penetration of the virion nucleic acid into the host cell. 3. Synthesis of the virus nucleic acid and protein by host cell machinery as redirected by the virus.4 Assembly of capsids and packaging of viral genomes into new virions. 5. Release of new virions from the cell
• Susceptible cell. Has a functional receptor for the virus and allows entry.
• resistant cell has no receptor which means virus cannot enter
• permissive cell has the ability to replicate viruses
• Growth curve for viruses growing in a cell culture 1. First inoculation happens and then the virus will enter the eclipse phase, here the viral genome and proteins will be replicated and translated. 2. The maturation phase, this begins when a new synthesized viral nucleic acid molecules becomes packaged inside their capsules. During this phase the number of infectious virions inside the host cell rises dramatically. The eclipse and the maturation phase comprise together the latent period because newly assembled virions are not yet presented outside the cell. 3. At the end of the muturation phase virions are are relesaed and the virus comes into a burst size which is the number of virions released per cell
• Steps in viruses growing 1. Eclipse period. 2. Muturation phase. 3. Burst size.
• Lytic vs lysogenic phase in bacteriophages In the lytic cycle bacterial cells are broken open and destroyed after replication of the virion, the virus will replicate and kill the host cell. As soon as the cell is destroyed the phage progeny can find a new host to infect. The lysogenic cycle allows the host cell to continue to survive and reproduce
• Direct penetration Penetration is used by non-enveloped viruses. The capsid of the genome enters the cytoplasm either by the direct injections or after fusion
• Membrane fusion Used by enveloped viruses, the viral envelope merges with the host cell membrane allowing the capsid to enter the cytoplasm.
• Endocytosis infection Used by both enveloped and non-enveloped viruses. The host cell engulfs the virus in a vesicle before releasing the viral genome
• How to enveloped and non-enveloped viruses exit the cell Enveloped viruses exit the cell through lysis and non-enveloped cell exit their host cell by budding from a cellular membrane
• Latent vs Persistant infections In latent infections virions are not produced and the virus lies dormant and can reactivate later and in persistent infections virions are not produced over time.
• What effects can can viruses have on its host cell The host cell can get a persistent infection, virulent infection, latent infection and can transform the host cell into tumor cells.
• Baltimore classification It bases the virus on how the synthesize mRNA
• +ssRNA vs -ssRNA In genetic material processing -ssRNA can transform to mRNA directly but +ssRNA needs first to become -ssRNA. In transcription +ssRNA is immediately translated into viral proteins and -ssRNA needs to be transcribed to +ssRNA first. In RNA replicase -ssRNA viruses carries RNA replicase in the virion and +ssRNA virus lets the host cell produce RNA replicase
• How do overlapping genes and viral polyproteins work? An overlapping gene is a gene whos nucleotide seuence overlaps with another gene, this will do so the virus has numerous ways to control the translation. It encodes more than one protein. A polyprotein is a single protein that can be cleaved into smaller proteins. It allows a virus to translate a large protein that is later cleaved into functional viral proteins
• Treatment of viruses Antibiotic does not work!!! There are antiviral drugs, vaccinations is a preventive treatment
• Prion A proteinaceous infectious particle and a misfolded protein that lacks RNA and DNA. No cure
• How do prions cause disease They cause neurological diseases by triggering normal proteins to misfold into abnormal shape. It spreads between individuals if you consume contaminated tissue

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