Viruses Flashcards
What are viruses
Viruses are infectious, highly specialised intracellular parasites
What does acellular mean and are viruses acellular
Viruses are acellular which means they are not made up of cells
What is the structure of a virus
Viruses usually have a geometric shape. They have a protein coat or capsid which is made up of repeating protein units known as capsomeres. They have genetic material stored in the centre of the virus. In some viruses the genetic material and protein coat is covered by a lipid envelope. They also have glycoprotein receptor spikes on their envelopes to help them attach to cell surfaces.
Why do most viruses cause damage and disease
Because natural viruses invade and take over living cells to reproduce and very few drugs can work on them
How do viruses attach to their host cells
By means of specific proteins (antigens) known as virus attachment particles that target proteins in the host cell surface membrane.
What are the different types of viruses
DNA viruses, RNA viruses and RNA retroviruses
What is the DNA in DNA viruses used for
The viral DNA acts directly as a template for both new viral DNA and for the mRNAs needed to induce synthesis of viral proteins
What is the RNA in RNA viruses used for
There are ssRNA which is a single strand of RNA and positive ssRNA viruses have RNA that can act directly as mRNA and be translated at the ribosomes. Negative ssRNA viruses cannot be directly translated the RNA must be transcribed before it is translated at the ribosomes
What is the RNA in RNA retroviruses used for
The single strand of viral RNA directs the synthesis of a special enzyme called reverse transcriptase and this goes on to make DNA molecules corresponding to the viral genome. This DNA is then incorporated into the host cell DNA and used as a template for new viral proteins and ultimately a new viral RNA genome.
What are the different ways DNA viruses replicate
Latency or the lysogenic pathway and the lytic pathway
What happens in the lysogenic pathway (latency)
Viruses that are non virulent insert their DNA into the host DNA so it is replicated every time the host cell divides. This DNA inserted into the host is a provirus. mRNA isn’t produced from the viral DNA as one of the viral genes causes the production of a repressor protein making it impossible to translate the rest of the viral genetic material during this period the virus is said to be latent
What happens in the lytic pathway
Sometimes the viral genetic material is replicated independently of the host DNA straight after entering the host. Mature viruses are made and eventually the host cell bursts releasing large numbers of new virus particles to invade other cells.
What are the different ways RNA viruses can replicate
Positive ssRNA Viruses are used directly as mRNA for translation into proteins at the ribosomes the proteins made include viral protein and RNA polymerase which is used to replicate the viral RNA. Negative ssRNA viruses are firstly transcribed into a sense strand. The virus then imports RNA replicase to transcribe the antisense RNA strand and produce a sense strand that can be translated at the ribosome. It then acts as mRNA at the ribosome and codes for viral protein.
How does RNA retrovirus replicate
They have viral RNA as their genetic material. It is translated into DNA by the viral enzyme reverse transcriptase in the cytoplasm of the cell. This viral DNA passes into the nucleus of the host cell where it is inserted into the host DNA. Host transcriptase enzymes then make viral mRNA and new viral genome RNA.
What are the different ways viruses can be spread
They can be spread through Infected mucus, droplets of saliva, infected blood or faeces or simple contact between organisms
