MI06: Introduction to Virology

How are viruses different than bacteria and eukaryotic cells?

Most viruses are known for their small size (e.g. filterable agents). But Amoeba viruses are so large (might represent a unknown branch).

Can viruses be treated with antibiotics?

No

What does a virus use from a host cell?

They make mRNA to be translated by host ribosomes since they cannot make their own proteins and generate energy for themselves.

Does a virus divide by binary fission?

They do replication (they cannot grow).

What is a virus?

It is an infectious and obligate intracellular parasite made of genetic material (DNA or RNA) surrounded by a protein coat.

How does a virus make more of itself? What parts of this process does a host cell provide?

The virus makes more of itself by replicating in a cell. They must produce mRNA that can be translated by the host ribosomes.

What are the structural characteristics of non-enveloped viruses?

They are surrounded by a capsid and have glycoprotein spikes for attachment.

What are the structural characteristics of enveloped viruses?

Lipid coating on the outside (derived from host plasma membrane).

What is a capsid? What makes up one?

It is a protein shell that surrounds the genome and composed of repeated units called capsomeres.

What is the envelope made of? What can be viral and what’s not?

It is made of lipid coating (outside) that is derived from the host plasma membrane.

Viral part: Protein/Glycoprotein spikes

Non-viral: Receptor

What is the receptor used for?

It is used to initiate entry by membrane fusion or receptor-mediated endocytosis.

How does envelope status affect transmission of the virus?

Depending on the type of envelope, the virus might have an easier/harder time entering cells.

Ex: Non-enveloped (protein = stronger), enveloped (lipids = weaker)

Which viruses can resist stomach acid better?

Non-enveloped viruses

Which viruses are more susceptible to desiccation/drying?

Enveloped viruses

Which are more likely to be transmitted by fomites?

Non-enveloped viruses

What are the different possibilities of nucleic acids that can make up viral genomes?

(+/-) ss/dsRNA and (+/-) ss/dsDNA

What is a virion?

Entire virus particle

What is a capsid?

A protein shell that is composed of repeated units called capsomeres (which can be either icosahedral or helical).

What is a nucleocapsid?

Capsid + Genome

What does the surface of a viral envelope / capsid contain?

Glycoprotein spikes

What are enveloped viruses more susceptible to?

Heat, desiccation, detergents, and pH

How do enveloped viruses attach to host cells?

They use viral attachment proteins which are spikes that are used for attachment.

How do envelope viruses enter or leave the host cells?

Released via budding.

Penetrates a cell by membrane fusion to enter host.

What are non-enveloped viruses covered on their surface?

Capsid (virus encoded protein shell)

How do non-enveloped viruses attach to a host cell?

They use glycoprotein spikes that come out of the capsid to attach to host cells.

How are non-enveloped viruses released from the host cell?

They are released from the cell by lysis.

Ex: Rhinovirus, norovirus, and papillomavirus.

What is the causative agent of COVID-19?

SARS-CoV-2

What type of virus is COVID-19?

• Enveloped

• ssRNA (+) genome

What is tropism for specific species or tissues seen in viruses?

Species: viruses choose to target humans or all mammals.

Tissues: viruses can choose to target epithelial cells, neurons, or white blood cells.

What does a permissive cell have?

• Proper surface receptors for the virus (attachment)

• Biosynthetic machinery to support the complete replicative cycle of the virus

What does not allow nonpermissive cells to replicate a particular strain of virus?

• Lacks a receptor

• Express an antiviral mechanisms that inhibits replication

What are the steps of viral replication?

1. Attachment: bind virion to host cell

2. Penetration: virus gain access to interior of cell

3. Uncoating: release genome from capsid

4. Transcription: viral genes (DNA/RNA) to mRNA

5. Translation: mRNA to protein

6. Replication: production of progeny copies of the virion nucleic acid

7. Assembly: production of new virions

8. Release: new virions leave cell

What are two ways that penetration can occur by viruses?

• Membrane fusion (only enveloped viruses)

• Receptor-mediated endocytosis

What viral structure is the target of neutralizing antibodies?

Viral attachment proteins

What helps viruses enter host cells?

Receptor

What is the attachment protein of SARS-CoV-2?

Spike

What is the cellular receptor of SARS-CoV-2?

Angiotensin Converting Enzyme II (ACE2)

What are the three ways that releasing a virus can happen?

• Budding: Capsid and proteins push out of cell membrane (enveloped virus)

• Cell lysis: Non-enveloped virus or enveloped gets a membrane from an organelle

• Exocytosis: Virus inside cell has membrane that fuses with lipid bilayer (non-enveloped and enveloped)

Which genome can be translated without any kind of replication?

+ssRNA

How can SARS-CoV-2 be released out of a host cell?

Release: exocytosis

How can SARS-CoV-2 enter/penetrate a host cell?

Membrane fusion

What is tropism?

Target cells that a virus is able to infect.

What does the viral family and genus name end in?

Family: -viridae

Genus: -virus

What is the Baltimore Classification of viral families that produce mRNA?

• Group I: dsDNA

• Group II: ssDNA

• Group III: dsRNA

• Group IV: ssRNA (+)

• Group V: ssRNA (-)

• Group VI: Retroviruses

• Group VII: Hepadnaviruses