Viral Pathogens: classification, biology, diseases 1 Flashcards
How are viruses classified?
NOT DUE TO PHYSICAL STRUCTURE E.G. MEMBRANE
- sturcture of viral genome
What are the diff types of viral genome?
Single stranded RNA - ssRNA
Double stranded RNA - dsRNA
Single stranded DNA - ssDNA
Double stranded DNA - dsDNA
How does double stranded and single stranded genomes differ in viruses?
Double stranded have base pairing
How do DNA and RNA genomes differ in viruses?
RNA genome is linear and segmented
DNA genome is linear OR CIRCULAR
How do genomes encode informations (genes) in viruses?
In either positive (5’-3’) or negative sense (3’-5’)
What is the central dogma?
process by which DNA instructions converted to functional product
What are the steps in central dogma in organisms?
Replication of DNA using DNA polymerase
Transcription of DNA into RNA using RNA polymerase
Translation of RNA into protein using ribosome
How do viruses use the central dogma differently?
RNA polymerase breaks down DNA into both +ve sense and -ve sense RNA
Reverse transcriptase converts RNA back to DNA
What is the baltimore classification?
virus classification depending on what type of genome it has (DNA or RNA)
What are the baltimore classification groups?
Group 1 - DNA+/- Group 2 - DNA+ Group 3 - RNA+/- Group 4 - RNA+ Group 5 - RNA - Group 6 - RNA + Group 7 - DNA +/-
What is the components of HIV?
2 copies of + sense RNA - genome
Protein layer and membrane layer
Reverse transcriptase (viral enzyme)
Capsid and glycoprotein envelope
Describe the structure of a mature HIV particle?
Outer envelope is a lipid bilayer with protruding heterotrimer spikes
Inside, shells of Gag proteins (in immature single shell of Gag proteins)
2 genomic RNA strands + tRNA and ciral enzyme
What are the 3 viral enzymes in HIV
PR, RT, IN
What are the 3 Gag proteins in HIV? and what does each do
MA - associates with membrane
CA - forms conical capsid
NC - coats viral RNA genome
What type of virus is HIV?
retrovirus
What 3 polyproteins can retroviruses synthesise?
Gag(antigen in viral core) , Pol(viral enzymes) and Env(envelope glycoproteins)
How does a retrovirus produce more than one type of protein for each polyprotein?
Multiple genes, splicing allows diff proteins of the 3 polyprotein types that can be produced
What are the regulatory/accessory protein in HIV? and what does each one do?
Tat - potent activator of viral transcription
Rev - mediates unspliced RNA nuclear transport
Vif - regulator of virus infectivity
Nef - immune modultor, T cell activation
Vpu - immune modulator and virus release
Vpr - cell cycle, virus nuclear export
define provirus + example
virus genome that is integrated into the DNA of a host cell
HIV does this
How does HIV RNA integrate it’s RNA into host DNA?
Reverse transcription
Long terminal repeats on either end of HIV RNA allowing binding to DNA
Regulatory RNA elements e.g. RRE and TAR
What are the steps of the retroviral replication cycle?
1) Entry
2) Reverse transcription
3) Integration
4) gene expression
5) assembly and release
How does a HIV retrovirus enter cell?
Viral envelope proteins engage with cellular receptors and fuse
Which HIV membrane proteins are involved in the entry of HIV into cells?
Trimer of gp41 and gp120 peptide subunits that is covered in glycans from post translational modifications
Which cellular receptors are involved in HIV entry into cell?
2 membrane proteins - CD4 and a chemokine receptor (CCR5 or CXCR4)
Describe the step by step mechanism of HIV entry into cell?
1) HIV binds to CD4 receptor in host cell
2) CoR (co-receptor) binding to membrane
3) 6 - HELIX BUNDLE FORMATION due to both above interactions - membrane fusion of viral lipid bilayer and cellular lipid bilayer
What cells does HIV target and why?
CD4 expressing cells (e.g. T cells and macrophages) which is what the receptor of HIV binds to
Which groups of the baltimore classification have to go through reverse transcription to form correct mRNA before protein produced?
Group 6 and 7
Why does HIV lead to AIDS?
Depletion of T cells and macrophages - immunodeficiency = aids
What happens once HIV has entered the host cell?
Uncoating and reverse transcription
Intracellular trafficking (using cellular microtubules)
Nuclear entry
Access to chromatin
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