Virology - Lecture 2 Flashcards Preview

2nd year - Microbiology > Virology - Lecture 2 > Flashcards

Flashcards in Virology - Lecture 2 Deck (38):
1

What are four things viruses need to survive?

1) Genetic material
-DNA, RNA
2) The ability to replicate
-Genome replication relies on host or viral genes
3) Gene expression
-Trasncription relies on host or viral genes (RNA polymerase)
-Translation relies on host translational machinery (ribosomes)
4) Structural integrity
-Capsid, envelope

2

What are the seven stages of the life cycle of a virus?

1) Binding
2) Entry
3) Uncoating
4) Viral gene expression
5) Genome replication
6) Virus assembly
7) Egress

3

Describe the first phase of viral life cycle (binding)

A viral ligand bind to a cellular receptor.
a host cell or organism is susceptible to infection by a particular virus if the host bears a cognate receptor for the virus

4

Describe the second phase of viral life cycle (entry)

Fusion
Endocytosis
Cell membrane disrutption

5

Describe the third phase of viral life cycle (uncoating)

Virus releases genetic material for gene expression and replication
Mediated by viral or cellular enzymes

6

Describe the fourth phase of viral life cycle (viral gene expression)

mRNA trascription often required
Translation using host ribosomes required
Some viruses encode their own transciptional machinery

7

Describe the fifth phase of viral life cycle (genome replication)

Virus may use host machinery
Some viruses encode viral replication machinery
ALL RNA viruses encode a viral polymerase for replication

8

Why do all RNA viruses encode viral polymerase for replication?

Host cells (humans) do not possess polymerase that turn RNA into DNA. Therefore, RNA viruses must possess an RNA dependent RNA-polymerase to carry out transcriptoin o the negative strand into the positive strand and then it can be translated by the host's ribosomes into proteins.

9

Describe the sixth phase of viral life cycle (virus assembly)

This phase is spontaneous

10

Describe the seventh phase of viral life cycle (egress)

Lysis
Exocytosis

11

Describe susceptibility

The ability of a virus to bind to a cellular receptor

12

Describe permissivity

the ability of a virus to replicate in a host cell/organism

13

Describe tropism

The range of cell types, tissues or organisms that are both susceptible and permissive to replication
Ex) Rabies virus has tropism for humans and many animals - it is a neurotropic virus

14

In the Baltimore Classification System of Viruses:
How many classes are there?

Seven

15

In the Baltimore Classification System of Viruses:
What is class I?

dsDNA viruses
-herpesviruses
-poxviruses
-papillomaviruses
-adenoviruses

16

In the Baltimore Classification System of Viruses:
What is class II?

ssDNA viruses
-parvoviruses
-circoviruses

17

In the Baltimore Classification System of Viruses:
What is common between class I and II (dsDNA & ssDNA)

Most use host DNA-dependent DNA polymerase to replicate genome
Rely on cellular replication machinery
Rely on host transcriptional and translational machinery

18

In the Baltimore Classification System of Viruses:
What is class III?

dsRNA viruses
-reoviruses

19

In the Baltimore Classification System of Viruses:
What is class IV?

(+)ssRNA viruses
-picornaviruses
-flaviviruses

20

In the Baltimore Classification System of Viruses:
What is class V?

(-)ssRNA viruses
-orthomyxoviruses
-rhabdoviruses

21

In the Baltimore Classification System of Viruses:
What is common between class III, IV & V ((dsRNA, (+)ssRNA & (-)ssRNA)?

These classes must encode an RNA-dependent RNA polymerase in their genome

(-)ssRNA viruses must package an RNA-dependent RNA polymerase in each viral particle

22

In the Baltimore Classification System of Viruses:
What is class VI?

(+)ssRNA viruses with a DNA intermediate
-retroviruses

23

In the Baltimore Classification System of Viruses:
What are some characteristics of class VI ((+)ssRNA with DNA intermediate)?

Require a virally encoded reverse transcriptase in the virus particle
Revers transcrition and viral integration are hallmarks of the retroviral family

24

In the Baltimore Classification System of Viruses:
What is class VII?

dsDNA viruses with an RNA intermediate
-Hepatitis B

25

In the Baltimore Classification System of Viruses:
What are some characteristics of class VII (dsDNA with RNA intermediate)?

Require a virally encoded reverse transcriptase for genome replication
Genomic DNA is transcribed into mRNA for viral gene expression
mRNA is revers transcribed by RT to make genome copies during replication

26

What does a lytic infection result in?

Results in host cell lysis
-rhabdoviruses

27

What does a lysogenic infection result in?

Results in virus production without cell lysis
-retroviruses, herpesviruses

28

Describe an acute infection

Infection characterized by a rapid production of virus and/or rapid onset of disease symptoms, followed by clearance by the host
-rhabdoviruses

29

Describe a persistent infection

Infections occur when the primary infection is not clears
-retroviruses, herpesviruses

30

Describe a chronic infection

Infections are persistent infections that are eventually cleared

31

How are viruses classified?

Classified by nucleic acid composition

32

What are the different types of latent infections?

Clinical and Molecular

33

Describe clinical latent infections

1) Clinical latency
- A period in which no symptoms of infection are observed
- Viral/pathogen replication may or may not be present
- HIV - after acute phase, patients experience a long period of clinical latency, where no symptoms exist but viral replication occurs and CD4+ T cell counts diminish

34

Describe molecular latent infections

2) Molecular latency
- A period in which no viral/pathogen replication occurs
- Features of latency vary by pathogen
- Herpesviruses - latent in neuronal or other cell types, express transcripts that prevent viral replication in order to hide from the host immune system

35

What does PAMP stand for?

pathogen-associated molecular patterns

36

Describe a PAMP response to infection

Derive from pathogens, common molecular features that indicate infection are:
-LPS
-flagellin
-dsRNA
-bacterial cell wall components
CpG DNA

37

What does DAMP stand for?

Danger-associated molecular patterns

38

Describe a DAMP resonse to infection

Derive from physiological changes that indicate damage
-ROS
-changes in cytoplasmic CA+/K+ concentrations
-ATP influx
-Crystal deposition (MSU, etc.)
-Membrane damage - mitochondrial, lysosomal, cell membrane