Viral Pathogens: Classification, Biology, Diseases I Flashcards
How varying are viral structures?
Various different viral structures with varying genomes (RNA/DNA)
How does structure effect viral function?
Adenoviruses and influenza viruses cause significant respiratory disease in humans although they differ greatly in structure, pathogenesis and their molecular biology
Outline the various configurations of viral genomes
- Single-stranded RNA (ssRNA)
- Double-stranded RNA (dsRNA)
- Single-stranded DNA (ssDNA)
- Double-stranded RNA (dsDNA)
What maintains the double stranded genomes?
Double-stranded genomes have complementary base pairing
Describe the structure of RNA genomes
RNA genomes can be linear and segmented i.e. more than one RNA per capsid
What is the structures of DNA viral genomes?
DNA genomes can be linear or circular.
What is Baltimore classification?
Viruses are grouped together by the way their genomes are grouped together (RNA/DNA)
Which nucleic acid do all viruses produce?
All viruses produce RNA which can be transcribed into protein to make new viruses
Describe HIV structure
Contains 2 RNA strands encapsulated by a protein capsid all covered by a lipid bilayer gathered by the virus as it emerges from the cell
What is the role of surface glycoproteins?
Protein sites / protein envelope glycoproteins on the cell surface mediate entry into the cell
Name the enzymes in HIV
HIV also houses integrase, reverse transcriptase and protease enzymes
Describe the outer structure of mature HIV
The outer envelope of HIV consists of a lipid bilayer with protruding Env spikes (heterotrimers of SU3TM3).
What structures lie within the envelope of mature HIV?
Inside the envelope lie shells of Gag proteins
In the immature particle, Gag itself forms a single shell
How is the mature HIV conical capsid formed?
MA (matrix protein) associates around the membrane CA (capsid protein) to form the conical capsid
What is the role of the nucleocapsid?
Nucleocapsid coats the viral RNA genome and bridges the interaction between the genome and the capsid as the variant forms
What are the 3 polyproteins synthesised by retroviruses?
- Gag
- Pol
- Env
What is contained within the HIV core?
The core contains two genomic RNA strands (plus strand) that the nucleosome binds, as well as tRNALys3, and ~50 copies of each viral enzyme (PR, RT, and IN).
What is the gag protein?
Gag; group specific antigen; viral core proteins; MA (matrix), CA (capsid), NC (nucleocapsid)
What is the Pol protein?
Pol; viral enzymes; protease (PR), reverse transcriptase (RT) and integrase (IN)
What is the Env protein?
Env; envelope glycoprotein; gp120 SU (surface); gp41 TM (transmembrane)
Name the accessory / regulatory HIV proteins present
- Tat
- Rev
- Vif
- Nef
- Vpu
- Vpr
Involved in immunoregulation to interact and try overcome complex human immune system
What is the role of the Tat accessory protein?
Potent activator of viral transcription
What is the role of the vpr protein?
Cell cycle, virus nuclear import (?)
What is the role of the regulatory Vpu protein?
immune modulator, virus release
What is the role of the Nef protein?
Immune modulator, T-cell activation, virus spread (?)
Describe the role of the regulatory Vif protein
Critical regulator of virus infectivity
Outline the role of the regulatory Rev protein in HIV
Mediates unspliced RNA nuclear export
What mechanism do retroviruses use to organise their genome?
Mechanism of Retroviruses: RNA is brought into cells via viruses and reverse transcribed into DNA
How is HIV RNA differentiated?
HIV RNA is split into different RNA structures that are recognised for different functions
What is the effect of reverse transcription in HIV?
Reverse transcription produces DNA version of the genes to be transcribed to produce all the protein products required as well as back into RNA
Describe the HIV outer envelope structure
HIV-1 Env consists of a trimer of gp41 and gp120 peptide subunits and is covered with glycans
These glycoproteins are large globular structures
How does HIV entry into cells differ from other retroviruses?
HIV entry at cell surface triggered by conformation changes driven by Env/receptor interactions
Contrasts with pH-dependent entry of adenovirus, influenza virus, etc
How does HIV gain entry into cells?
HIV-1 entry requires two membrane proteins:
CD4 (T-cells) and a chemokine receptor (CCR5/CXCR4)