Viral Pathogens: classification, biology, diseases 1

Question 1

How are viruses classified?

Answer 1

NOT DUE TO PHYSICAL STRUCTURE E.G. MEMBRANE

• sturcture of viral genome

Question 2

What are the diff types of viral genome?

Answer 2

Single stranded RNA - ssRNA
Double stranded RNA - dsRNA
Single stranded DNA - ssDNA
Double stranded DNA - dsDNA

Question 3

How does double stranded and single stranded genomes differ in viruses?

Answer 3

Double stranded have base pairing

Question 4

How do DNA and RNA genomes differ in viruses?

Answer 4

RNA genome is linear and segmented

DNA genome is linear OR CIRCULAR

Question 5

How do genomes encode informations (genes) in viruses?

Answer 5

In either positive (5’-3’) or negative sense (3’-5’)

Question 6

What is the central dogma?

Answer 6

process by which DNA instructions converted to functional product

Question 7

What are the steps in central dogma in organisms?

Answer 7

Replication of DNA using DNA polymerase
Transcription of DNA into RNA using RNA polymerase
Translation of RNA into protein using ribosome

Question 8

How do viruses use the central dogma differently?

Answer 8

RNA polymerase breaks down DNA into both +ve sense and -ve sense RNA
Reverse transcriptase converts RNA back to DNA

Question 9

What is the baltimore classification?

Answer 9

virus classification depending on what type of genome it has (DNA or RNA)

Question 10

What are the baltimore classification groups?

Answer 10

Group 1 - DNA+/-
Group 2 - DNA+
Group 3 - RNA+/-
Group 4 - RNA+
Group 5 - RNA -
Group 6 - RNA +
Group 7 - DNA +/-

Question 11

What is the components of HIV?

Answer 11

2 copies of + sense RNA - genome
Protein layer and membrane layer
Reverse transcriptase (viral enzyme)
Capsid and glycoprotein envelope

Question 12

Describe the structure of a mature HIV particle?

Answer 12

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

Question 13

What are the 3 viral enzymes in HIV

Answer 13

PR, RT, IN

Question 14

What are the 3 Gag proteins in HIV? and what does each do

Answer 14

MA - associates with membrane
CA - forms conical capsid
NC - coats viral RNA genome

Question 15

What type of virus is HIV?

Answer 15

retrovirus

Question 16

What 3 polyproteins can retroviruses synthesise?

Answer 16

Gag(antigen in viral core) , Pol(viral enzymes) and Env(envelope glycoproteins)

Question 17

How does a retrovirus produce more than one type of protein for each polyprotein?

Answer 17

Multiple genes, splicing allows diff proteins of the 3 polyprotein types that can be produced

Question 18

What are the regulatory/accessory protein in HIV? and what does each one do?

Answer 18

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

Question 19

define provirus + example

Answer 19

virus genome that is integrated into the DNA of a host cell

HIV does this

Question 20

How does HIV RNA integrate it’s RNA into host DNA?

Answer 20

Reverse transcription
Long terminal repeats on either end of HIV RNA allowing binding to DNA
Regulatory RNA elements e.g. RRE and TAR

Question 21

What are the steps of the retroviral replication cycle?

Answer 21

1) Entry
2) Reverse transcription
3) Integration
4) gene expression
5) assembly and release

Question 22

How does a HIV retrovirus enter cell?

Answer 22

Viral envelope proteins engage with cellular receptors and fuse

Question 23

Which HIV membrane proteins are involved in the entry of HIV into cells?

Answer 23

Trimer of gp41 and gp120 peptide subunits that is covered in glycans from post translational modifications

Question 24

Which cellular receptors are involved in HIV entry into cell?

Answer 24

2 membrane proteins - CD4 and a chemokine receptor (CCR5 or CXCR4)

Question 25

Describe the step by step mechanism of HIV entry into cell?

Answer 25

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

Question 26

What cells does HIV target and why?

Answer 26

CD4 expressing cells (e.g. T cells and macrophages) which is what the receptor of HIV binds to

Question 27

Which groups of the baltimore classification have to go through reverse transcription to form correct mRNA before protein produced?

Answer 27

Group 6 and 7

Question 28

Why does HIV lead to AIDS?

Answer 28

Depletion of T cells and macrophages - immunodeficiency = aids

Question 29

What happens once HIV has entered the host cell?

Answer 29

Uncoating and reverse transcription
Intracellular trafficking (using cellular microtubules)
Nuclear entry
Access to chromatin

Question 30

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