Virus genomes and proteins Flashcards
Do RNA viruses have a big or small genome?
Small generally
What is a virus?
Nucleic acid enclosed in a protein coat
Do eukaryotes contain RNA dependent RNA polymerase?
No
How error prone are viral RdRps?
Very
Do viral RdRps contain error correction and what does this mean for the virus?
No, more mutations leading to quick evolution
How do RNA viruse prevent too many errors amounting?
By having a small genome
Are coronavirus genomes big or small?
Big
How do coronaviruses correct genome mistakes?
Their RdRps have proofreading
What sense virus carried RdRp on the end of its strand?
Negative sense
What is the IRES?
Internal ribosome entry sites
Function of the IRES
Virus genome folds up, the RNA molecule folds up and can interact with eachother forming H bonds. THese interact with host machinery to initiate transaltion.
Examples of Flaviviruses (+)
Dengue fever virus
Yellow fever
West nile virus
Tick borne encephalitis
Flavivirus genome
Single ORF encoded polyprotein which is cleaved into indicidual polypeptides.
How is Hep C different from Flaviviruses?
Instead of a cap it has an IRES which initiates transalation
Picornavirus examples (+)
Poliovirus, rhinovirus, Hep A virus.
Alpha virus examples
Eastern equine encephalitis virus
Structure of alphavirus (+)
M7G cap, poly A tract, mimicing mRNA. Two ORFs encode two polyproteins.
Coronavirus examples (+)
SARS, SARS-Cov2, MERS
Structure of coronavirus genome
Multiple ORFs. A m7G cap and poly(A) tail. There is negative-strand production and then transcription of sub-genomic RNAs which are then translated into the virus proteins.
Retrovirus examples
Mo-MLV, HTLV and HIV
Are retrovirus postive or negative sense?
Positive
How many copies of genome are encapsulated in a retrovirus?
Two
Example of negative sense non segmented viruses?
Rhabdoviruses
Examples of rhabdoviruses (-)
Rabies virus and vescular stomatisis virus (VSV).
Structure of rhabodoviruses (-)
Poly U tract, terminator and promotor sequence. Monoscitronic RNA mimics cellular mRNA, freq of mRNA declines.
Examples of filoviruses? (-)
Ebola and Marburg
Genome structure of filoviruses?
Genes defined by hihgly conserved transcriptional start signals at theri 3’ and termination signals at their 5’ ends.
Example of orthomyxoviruses?
Infleuenza, negative sense and 8 segments.
Examples of linear DNA viruses
Adenovirus, Herpesvirus, Poxvirus
Examples of circular DNA viruses
Papoviruses
Hepadnaviruses
Parvoviruses
Example of ssDNA virus
Parvovirus
Features of human DNA viruses
All have origins of DNA replication. Most use host DNApol. Most replicate in cytoplasm.
Features of adenoviruses
Inverted terminal repeats (ITR) contain origin of DNA replication. Terminal protein (TP) is linked to 5’ ends.
Herpesvirus features
Long and short regions flanked by inverted repeats. 3 origins of DNA replication seperated through genome.
Papillovirus features
Early and late expressed genes
Overlapping reading frames
What virus is the leading cause of cervical carcinoma?
Human papillomaviruses
What charge do capsid proteins usually have?
Highly positive
What residues are capsid proteins rich in
Arg and Lys
Two forms of capsid protein structure
Helical, or icosahedral
Picornavirus capsid protein structure
Four protein form basic unit, 60 form icocasehrdal head. Negative charge of RNA is counteracted by Na+ and K+ ions
When are matrix proteins present?
In enveloped viruses
What is the matrix protein in herpesviruses called?
Tegument
What protein makes up the retroviral matrix?
Matrix aantigen (MA/p17)
Role of viral glycoproteins?
Mediate fusion between viral and cellular membranes, regulated fusogenic activity.
how does the gp160 HIV-1 glycoprotein mature?
Proteolytic cleavage –> gp120 and gp41
