Micro. Chapter 6: Acellular Pathogens

Host Range

• What the virus can infect

• Normally only one or two species

Viral tropism

• The type of cell or tissue a virus can infect

Viral Genetic Make-up

• DNA or RNA

• Single or multiple strands

• Single or double stranded

• Linear or circular

Capsid coat

• Surrounds the viruses genetic information

• Made of capsid protein

Spike Protein

• Viral Accessories

• Juts out of the protein

• Involved in viral uptake

Envelopes

• Piece of stollen cell membrane from infected cell

• Used to disguise virus

Bacteriophages

• Have a icosehedral head

• Infect bacteria

• Don’t have envelopes

• Multiplication cycle

- Attachment

- Penetrate

- Biosynthesis

- Mature and assemble

- Release

Lytic phages/cycle

• Replication process

• Virus genome enters

• Host cell makes more of the virus

• Virus exits and blows up the cell

Temperate phages/lysogenic cycle

• Replication cycle

• Virus genome enters

• Integrate with host DNA - prophage

• Replicates when host cell replicates

• May eventually become lytic

Transduction

• When phages transfer pieces of bacterial DNA between bacterial cells

• Often accidental

- Packaging error

- Generalized transduction

Uncoating

• One additional step added to the viral replication process in animal cells

• Releases nucleic acid

dsDNA

ssDNA

• Type of viral DNA

• Moves to the nucleus of the host cell

• Uses the host cell machinery to become complimented and replicated

- Protein is then replaced from it

dsRNA

• Type of viral RNA

• Moves to the nucleus of the host cell

• Uses the host cell machinery for replication and protein synthesis

+RNA

• Type of viral RNA

• “+” tells the direction, 5 to 3

- This is the normal direction of host RNA

• Can’t be replicated but can be used by ribosomes to make proteins

-RNA

• Type of viral RNA

• “-” tells the direction, 3 to 5

- This is opposite of the normal direction of host RNA

• Can’t be replicated by the cell or used by ribosomes to make protein

- Uses viral enzyme to make a complementary “+” strand that can be used for protein synthesis

Retroviruses

• Ultimately +RNA

• Once inside the cell they convert to ssDNA

- RNA used as a template to make DNA

Polymerases

• An enzyme that replicates nucleic acid

• Two subcategories: DNA dependent DNA polymerase and DNA dependent RNA polymerase

RdRP

• The viral enzyme that creates complementary “+” strips of RNA

- Needed for viral protein synthesis of -RNA

Acute Viral Infection

• Symptoms are shown

- Ex: The flu

Latent Viral Infection

• Stays in tissue dorment

Chronic Viral Infection

• Long time, recurring infection

- Ex: HIV

CPE

• Direct detection of virus

• Looks for damage on a host cell that is caused by the virus

Hemagglutinin

• Indirect detection of virus

• Test for viral proteins that clump RBC

PCR

• Indirect detection of virus

• Detects viral genome material

Immunoassays

• Indirect detection of virus

• Detects virus itself and antibodies

Viroids

• Viruses that don’t have a capsid coat

- Just nucleic acid

• None infect animal or humans

Satellite viruses

• Effect animals cells

• Viral helper RNA

• Can’t cause disease on their own but can help other viruses

Virusoids

• Effect plant cells

• Viral helper RNA

• Can’t cause disease on their own but can help other viruses

Prions

• Misfolded form of a protein that causes other proteins of the same type to misfold

• Causes plaques

• Highly resistant to destruction

Plaques

• The black spots in a Petri dish