Virology: Basics

Which are the 4 criteria of a microorganism to be considered a virus?

1. Only one type of NA (DNA or RNA)

2. It can’t growth or divide

3. Obligate intracellular paratisism

4. A define structure

What does it mean when we say viruses obligate intracellular paratisism?

Because they lack of enzymatic or energetic systems they are using the cell to replicate.

What is the virion?

Mature, infectious, extracellular viral particle

What does the virion contain?

It contains:

-genome

-capsid

(-envelope)

Which are the charcteristics of the DNA genomes?

1. genome size is variable

2. most often 3D 2-stranded and linear

Please tell me one example of 1. single stranded DNA virus 2. Double stranded (a. linear, b.circular) 3. partially double stranded

1. parvoviridae

2. a. adenoviridae b. papillomaviridae,

3. Hepadnaviridae

Which are the charcteristics of the RNA genomes?

1. Needs a viral RNA dependent RNA polymerase to replicate

2. Most often single-stranded and linear

Please tell me one example of 1. single stranded RNA virus (a. diploid b. linear, b. segmented) 2. Double stranded (segmented)

1. a. retroviridae b. coronaviridae, c. orthomyxoviridae

2. reoviridae

In what RNA genomes are divided?

1. Positive-strand: can act as mRNA and can immediately translated into proteins (coronavirus)

2. Negative-strand: has to be trancribed first (influenza virus)

Which are the special characistics of the RNA genome?

1. A cap at the 5’ terminal end

2. A poly-A Sequence at the 3’ terminal end

3. A viral protein covalently attached to the 5′ end acts as a primer during RNA synthesis (Picornaviridae)

Which are the roles of capsids?

1. Protect the genome from the environment

2. For naked viruses, take part in the attachment of the virus to the host cell.

Tell me the characteristics of the viral capsid.

1. Resistant and very stable structure

2. Limited viral genome coding capacity

3. Principe of self-assembly

How capsid is formed?

By polymerization of 1 or a small number of proteins.

Which are the 2 main shapes of capsid?

1. Tubular capsid with helical symmetry

2. Icosahedral capsid with cubic symmetry

Helical capsid: most of them are _____-sense RNA virus.

Negative

All helical animal viruses are ________.

Enveloped

Envelope: 1. from what they are composed of? 2. are they stable?

1. Complex composition with lipids and glycoproteins.

2. Very sensitive to physico-chemical actions and to environmental conditions.

How do viruses aquire their envelope?

By budding through a cellular membrane.

What are spikes?

Projections verticle to the surface.

What is the HIV1 spike (monomera, dimer, trimer)?

Trimer

How do we classify a virus?

1. Species

2. Genus

3. Family

4. Order

5. Class

6. Phylum

7. Kingdom

or baltimore classification

Which are the different steps in the viral replication cycle?

1. Attachment

2. Penetration

3. Uncoating

4. Replication

5. Trancription/Translation

6. Assembly

7. Release

What is the definition of viral attachment?

Interactions between viral glycoproteins, proteins and cellular receptors.

Which are the different strategies for penetration?

1. Endocytosis: naked or enveloped viruses

2. Fusion: only enveloped viruses

3. Translocation: poliovirus

What is happening during fusion?

Penetration of the nucleocapsid into the cytoplasm