Virology (1) Flashcards
(21 cards)
What are 4 possible shapes viruses can come in?
1) Head and tail
2) Helix
3) Icosahedron
4) Variable - pleomorphic
What is an example of a head+tail virus?
1) Bacteriophage X174
2) Head contains nucleic acid - ssDNA
3) Tail penetrates host cell wall to allow injection of phage DNA
What is an example of a helical virus?
Tobacco Mosaic Virus - TMV
What is an example of an icosahedral virus?
1) Polio
2) Capsid proteins arranged in icosahedral form (20 faces)
3) Polio capsid compromises 4 different glycoproteins - VP1, VP2, VP3 and VP4
What is an example of a variable/pleomorphic virus?
1) Influenza
2) Irregularly shaped particles 80-120nm
3) Membranes fused together
What is an example of an enveloped virus?
1) Herpes
2) Lipid envelope gives ‘fried egg’ appearance
3) Core virus particle contains dsDNA - 120-200nm
What is the basic structure of virus particles?
1) Protein outer coat including surface glycoproteins - capsid proteins form into regular structures (capsomers) which gives its symmetry
2) Nucleic acid + protein = nucleocapsid/virion
3) Each virus particle forms characteristic shape relates to size of particle + biochemistry of capsomers
What is the aim of replication in viruses?
1) Produce more copies of viral genome
2) Produce viral proteins - structural capsid proteins + enzymes to help replication of genome
How does replication work for dsDNA and ssDNA viruses?
1) Host RNA polymerase transcribes mRNA from viral DNA
2) Viral mRNA feeds into host protein synthesis mechanisms
3) Viral proteins either make enzymes (e.g., viral DNA polymerase to make more copies of genome), viral proteins to make new capsids
What is the process for replication of ssRNA viruses (positive and negative sense)?
1) Positive - viral genome acts as mRNA, feeds into host protein synthesis mechanisms
1) Negative - Viral RNA polymerase copies genome and then acts as mRNA, feeds into host protein synthesis mechanisms
2) Viral proteins make either enzymes (e.g., viral RNA polymerase to make more copies of genome) or make new capsids
What is the process for replication of dsRNA viruses?
1) Viral RNA polymerase transcribes viral mRNA
2) Viral proteins make either enzymes (e.g., viral RNA polymerase to make more copies of genome) or make new capsids
What is the process of replication of retroviruses (positive sense ssRNAs)?
1) Viral reverse transcriptase enzyme uses viral RNA as template to make negative sense ssDNA - host enzymes copy to make dsDNA strand integrated into host genome, feeds into host protein synthesis mechanisms
2) Viral proteins make either enzymes (e.g., viral reverse transcriptase to make more copies of genome) or make new capsids
What are the 2 main approaches to classifying viruses?
1) Baltimore - based on molecular principles
2) International Committee on Taxonomy of Viruses system - based on biological principles of taxonomy
How does the baltimore system class viruses?
1) Group I - dsDNA viruses
2) Group II - ssDNA viruses
3) Group III - dsRNA viruses
4) Group IV - positive sense ssRNA viruses
5) Group V - negative sense ssRNA viruses
6) Group VI - RNA reverse transcribing viruses
7) Group VII - DNA reverse transcribing viruses
How does the International Committee on Taxonomy of Viruses group viruses?
Split into realm, kingdom, phylum, class, order, family, genus and species
What suffixes are used to indicate level of classification?
1) Order - …..virales
2) Family - …..viridae
3) Subfamily - …..virinae
4) Genus - …..virus
5) Species - Name of virus
What is the structure of polio virus?
1) Capsid protein (Viral Protein, VPs) - there are 4 types
2) VP 4 is not visible as it is enclosed by other VPs
How does polio virus infect the human host?
1) Virus particles infect human gut epithelial cells and (rarely) neurones in CNS
2) Once virus entered host cell - replicates quickly and produces progeny within about 6hrs
How does polio replicate?
1) Virus particle uses surface capsid glycoproteins (VPs 1-3) to attach to receptive host cell
2) Bind to host cells with receptor CD155 (only) - e.g., gut epithelium
3) VP 4 is lost from virus particle during process of entry into host
4) Virus ‘uncoats’ in cytoplasm and genome released
5) Replication occurs inside cytoplasm of host cell
6) Polio is positive sense RNA, acts as mRNA inside cells
7) Migrates to ribosomes where translation takes places
What are the symptoms of poliomyelitis?
1) Minor flu-like symptoms such as fever, sore throat, tiredness and sometimes headaches/vomiting
2) Paralytic poliomyelitis has symptoms of meningitis, encephalitis and flaccid paralysis
3) In paralytic poliomyelitis intercostal muscles are also affected
How is polio identified in the lab?
1) Faecal samples
2) PCR
3) Use vaccine to prevent polio
