Microbiology 4: Viral properties Flashcards
Describe a generic virus replication cycle
1)Attachment to the host cell by specific interaction between the virus attachment protein and a host cell receptor (a molecule on the surface of a host cell that has a completely different role but that the virus has evolved to use as its key for entry to the interior of the cell). 2)Entry of the virus genome to the host cell and synthesis of viral mRNA (primary transcription) 3) Translation of viral mRNAs into viral proteins by host cell ribosomes in the cytoplasm 4)Replication of the viral genome, usually by making a small number if complementary copies that are then themselves copied at high numbers into new genomes (asymmetric replication) 5)Assembly of the virus proteins into new virons, association and encapsidation of the new genomes 6) Exit from the infected cells and dissemination to new hosts?
What is the cytopathic effect and how does it lead to cell death?
If you put a virus on healthy cells you get a change in cell shape and you get cell death.
This is the CYTOPATHIC EFFECT (CPE) which is defined as the death of the cell as a result of being infected by a virus.
The CPE could be due to the virus taking over your genetic machinery so that the cell is no longer able to produce the proteins that it needs to survive - the cell is destined to die.
Death is probably due to apoptosis In other words: virus has to compete with host proteins synthesis - they do this in such an aggressive way that it destroys the capability of the host cell to use its own machinery
Describe how viruses are detected?
-Electron microscope -We also “see” viruses by their effects on their hosts. Thos can be a plant or animal (in vivo) or cells cultured in the laboratory (in vitro) e.g. cytopathic effect syncytia, inclusion bodies, membrane blebbing
what is a plaque assay used for and how does it work?
Viruses form plaques in cell monolayers.
As a result of this death - viruses form plaques on cell monolayers. Plaques - the result of an INDIVIDUAL virus infecting one cell and then infecting other cells. Each plaque is the result of one single virus that was originally put onto the cell monolayer.
If you count the plaques you can measure how many viruses there were in the sample. Someone who is freshly infected will have fewer plaques than someone who has had it for a while .This is used to find out how much virus is in the patient and is done using Plaque Assay
What is syncytia and name a virus that can cause syncytia formation?
Some viruses don’t make plaques - they do other things to the cell such as syncytia formation. In this image - there is a big bundle of cells in the middle which have stuck together (effectively becoming one massive cell with many nuclei) HIV has the ability to fuse at the cell membrane.
When a cell has been infected by HIV, it begins expressing HIV glycoproteins on their surface. One cell can fuse with another cell because of the interaction between the HIV protein and the receptor on the opposite cell In the laboratory, this is way you can visualise whether there is a virus or not in a sample You can take a sample of blood, drop it on some susceptible cells and if you see syncytian formation, it suggests that there is virus present add pic
How would you detecta virus which produces little visable change on the cells?
Immune florescence Antibodies generated in the lab to unique virus proteins indicate which cells are infected or where in the cell the virus proteins are located.
List the different ways Viruses can be diagnosed (in a lab)?
Detecting Viral Genome PCR Have primers which are complementary to a specific part of the viral genome which identifies the virus Use sets of primers and the one which shows up positive will identify the virus Detecting Viral Antigen Indirect Fluorescence Antibody (IFA) ELISA Detecting Viral Particles Electron Microscopy Haemagglutination Assay Detecting virus cytopathic effect in cultured cells Virus isolation Detecting antibodies to virus Serology
Why can propagating viruses be useful?
We can passage viruses in the lab by providing permissive cells Viruses may accumulate mutations that adapt them to the new host (e.g. losing some accessory genes) This can lead to ATTENUATION and was the basis of generation of vaccines in the past .
Why and how can viruses be manipulated?
Virus genomes are so small they can be synthesized This allows reverse genetics, the creation of viruses at will with engineered mutations in their genomes.
Define virus
Viruses are infectious OBLIGATE intracellular PARASITES. A virus has a genome that comprises DNA or RNA. Within an appropriate cell, the viral genome is replicated and directs the synthesis, by cellular systems, of more viral components and genomes. The components effect the transport of replicated viral genomes through the environment to new host cells.
What is used nowadays to classify viruses.
Baltimore classification system which places viruses into groups depending on the pathway they use to make their genomes into mRNAs.
