Viruses and Prions

What are some components found in a typical virus?

Every Virion- Nucleic acid genome, protein capsid

Some Virions- Lipid envelope with virus protein strikes and replication enzymes

What does a viral capsid consist of?

Protein Capsomeres/ protomeres

What are the different types of viral morphologies?

Polyhedral/cosahedral

Helical

Comples

Polyhedral/cosahedral

20 triangular faces and 12 vertices

Helical

Capsid proteins surrounding nucleic acid coil in hollow tube.

What is the Lipid Membrane?

Not the same as cell membrane as it has host and viral components.

Has viral proteins that may look like spikes and attach to host cell.

Viral Genomes

DNA or RNA

Single-stranded or double-stranded

Linear or circular

5 stages of viral replication

1. Attachment to host cell

2. Entry of virus/viral genome into cell

3. Synthesis of essential replication components

4. Assembly of nucleocapsids

5. Release of virions from cell

Attachment

Specific interaction between viral proteins and host cell receptors.

What happens when receptors are found in one species?

It limits the cells the virus can infect.

What happens if receptors are found in more than one species?

Virus has a broad host range

What are the 3 possibilities of entry and how does it work?

Endocytosis- non-enveloped or enveloped

Fusion- enveloped only

Injection- bacteriophages only

What often causes cell lysis when viruses release during replication?

Naked viruses

What often causes cytolysis?

Escape of virions

How does enveloped viruses use budding?

Viral proteins are inserted into host cellular membrane.

Viral capsid associates with viral proteins in the membrane.

Virions bud out from membrane

Replication of a simple naked dsDNA virus

1. Virions binds to host cell

2. Nucleocapsid enters host cell

3. Viral dsDNA is copied, Viral mRNA is transcribed, viral proteins are translated

4. Virions self-assemble

5. Cell Lyses and virions are released

Replication of a Typical Enveloped DNA Virus

1. Membranes Combine

2. Endocytosis or membrane fusion is used for entry

3. Viral components are replicated

4. Nucleocapsid matures in cell

5. Virus buds from the cell, taking a chunk of membrane with it.

3 Types of Viral Infections

1. Ones that don’t affect the cell

2. Ones that affect the cell, but don’t kill the cell

3. Ones that kill the cell

What happens when lambda repressor is expressed?

Cro is repressed and cl is activated

What happens when Cro is expressed?

cl is repressed and Cro is activated

Four Principles to Establish a Universal Virus Taxonomy

1. It should reflect evolutionary history

2. Placement should reflect other non-molecular traits so longs as group is monophyletic.

3. Taxonomy is one way of classifying viruses; others should be considered

4. Strict sequence quality control is important

Viroids

Nucleic-acid based nonviral acellular infectious agents

No protein capsids and protein coding genes

Prions

Protein-based nonviral acellular infectious agents.