BIOL 2401 Week 5 Unit 3.2: Viruses

WHy are viruses considered acellular?

Because they aren’t made of cells, and are just nucleic acid surrounded by protein

Obligate intracellular parasite

Term used to describe viruses, since they must reproduce inside a cell and use the cell’s resources to replicate

Virion

Developed infectious viral particle allowing transmission from one host cell to another

Components of a virion

Nucleic acid (linear or circular), capsid, ± envelope

Can a virion’s nucleic acid be both DNA and RNA?

No, a virion’s nucleic acid is either DNA or RNA

Can a virion’s nucleic acid be both single-stranded and double-stranded?

Ni, a virion’s nucleic acid is either single-stranded or double-stranded

Capsid

Protein code made of capsomeres surrounding the nucleic acid

Capsomere

Protein subunits which make up the capsid

Shapes of capsids

Helical, polyhedral, complex

Virion envelope

Structure not present in all viruses made from phospholipid bilayer containing carbohydrates and proteins. Dervied from host cell membrane, may have spikes (glycoproteins)

Spikes (in virion evelope)

Glycoproteins used to attach to host cells

HIV, Hepatitis B, Influenza, Coronavirus, are examples of ___________ viruses

Enveloped

Adenoviruses and Norovirus are examples of ____________ viruses

Non-enveloped

Order of viral taxonomy

Order → family → genus → species

If viruses are acellular and not living, how are they classified?

By using nucleic acid, capsid morphology, size, envelope, host range, disease, and strategy of replication

Virus family suffix

-viridae

Virus genus suffix

-virus

Steps in animal virus replication (AEUBAR)

Attachment → Entry → Uncoating → Biosynthesis → Assembly → Release

What does the nucleic acid in viruses code for?

It codes for how to make the capsid, and enzymes that process their nucleic acid

Attachment in animal virus replication

Viruse spikes attach to host cell receptor sites

Entry in animal virus replication

The entire virion enters the host cell.

• Non-enveloped viruses enter via endocytosis

• Enveloped viruses enter via fusion

Uncoating in animal virus replication

Genetic material of the virus is released from the capsid

Biosynthesis in animal virus replication

Virus “hacks” cell metabolic pathways, forming new virions.

Biosynthesis of DNA viruses

Viral DNA in host cell cytoplasm enters nucleus. mRNA transcribed and moves to cytoplasm, mRNA translated by ribosomes to produce capsid proteins

Assembly of DNA viruses

Capsid proteins re-enter nucleus and join with replicated viral DNA, forming new virions

Biosynthesis of RNA viruses

Assembly of RNA viruses

Biosynthesis of RNA viruses: retroviruses

Release in animal virus replication

Where the viruses escape through cell lyis, exocytosis, or budding