Microbiology Chapter 13

How do some viruses lead to cancer?

A transformed cell harbors a tumor-specific transplant antigen (TSTA) on the surface and aT antigen in the nucleus

What is the lytic cycle of bacteriophage infection?

1. Attachment: phage attaches by the tail fibers to the host cell 2. Penetration: phage lysozyme opens the cell wall; tail sheath contracts to force the tail core and DNA into the cell 3. Biosynthesis: production of phage DNA and proteins 4. Maturation: assembly of phage particles 5. Release: phage lysozyme breaks the cell wall

What is the lysogenic cycle of bacteriophage infection?

Lysogeny: phage remains latent -Phage DNA incorporates into host cell DNA -Inserted phage DNA is known as a prophage -When the host cell replicates its chromosome, it also replicates prophage DNA -Results in phage conversion—the host cell exhibits new properties

Characteristics of prions.

PRIONS: Proteinaceous infectious particles PrPc: normal cellular prion protein, on the cell surface. PrPsc: scrapie protein; accumulates in brain cells, forming plaques No virion structure or genome It was first thought it was a virus. Elicits no immune response Extremely resistant to inactivation by heat, disinfectants & radiation Can even survive autoclaving You need to hydrolyze the protein to destroy the protein

How do prions replicate?

The protein itself does not self-replicate and the process is dependent on the presence of the polypeptide in the host organism

What are oncogenes?

Transform normal cells into cancerous cells

Virion

complete, fully developed viral particle Nucleic acid—DNA or RNA can be single- or double-stranded; linear or circular

complex virus

complicated structures

Plant viruses

enter through wounds or via insects Plant cells are generally protected from disease by an impermeable cell wall

Bacteriophages

grown in bacteria Bacteriophages form plaques, which are clearings on a lawn of bacteria on the surface of agar Each plaque corresponds to a single virus; can be expressed as plaque-forming units (PFU)

helical virus

hollow, cylindrical capsid

Envelope

lipid, protein, and carbohydrate coating on some viruses

polyhedral virus

many-sided

What diseases are caused by viroids?

potato spindle tuber disease Citrus gummy bark viroid Cucumber pale fruit viroid Coconut cadang-cadang viroid Avocado sunblotch viroid *Hepatitis D possibly a viroid

Spikes

projections from outer surface

Capsid

protein coat made of capsomeres (subunits)

Oncogenic viruses

Become integrated into the host cell's DNA and induce tumors.

What is the function of the viral envelope and accessory proteins/spikes?

Envelope is a phospholipid bilayer that protects virus and helps it enter into host cells. spikes help the virus attach to the surface of the host cell.

Examples of oncogenic viruses.

DNA Oncogenic Viruses: Adenoviridae Herpesviridae- Epstein-Barr virus Poxviridae Papovaviridae- Human papillomavirus Hepadnaviridae-Hepatitis B virus RNA Oncogenic Viruses Retroviridae- Viral RNA is transcribed to DNA (using reverse transcriptase), which can integrate into host DNA HTLV-1 and HTLV-2 cause adult T cell leukemia and lymphoma

What are the different types of nucleic acid and replication schemes that viruses can have?

DNA viruses replicate their DNA in the nucleus of the host using viral enzymes RNA Virus multiplies in the host cell's cytoplasm using RNA-dependent RNA polymerase Single-stranded RNA, produce DNA Use reverse transcriptase to produce DNA from the viral genome. Viral DNA integrates into the host chromosome as a provirus

What are the major differences in the replication of RNA versus DNA viruses and viruses that use reverse transcriptase?

DNA viruses replicate their DNA in the nucleus of the host using viral enzymes Synthesize capsid in the cytoplasm using host cell enzymes. RNA Virus multiplies in the host cell's cytoplasm using RNA-dependent RNA polymerase --ssRNA; + (sense) strand Viral RNA serves as mRNA for protein synthesis --ssRNA; - (antisense) strand Viral RNA is transcribed to a + strand to serve as mRNA for protein synthesis --dsRNA—double-stranded RNA. Single-stranded RNA, produce DNA Use reverse transcriptase to produce DNA from the viral genome Viral DNA integrates into the host chromosome as a provirus.

What are the differences between entry and exit for enveloped vs naked viruses?

Entry : -enveloped viruses merge membranes/ -non enveloped viruses engulf Exit: -enveloped viruses leave through budding (does not kill host cell) -nonenveloped viruses exit through Lysis (killing the cell)

What is found in only some viruses?

Envelope—lipid, protein, and carbohydrate coating on some viruses Spikes—projections from outer surface

What are the multiplication steps for a virus? What happens at each step?

For a virus to multiply: It must invade a host cell It must take over the host's metabolic machinery 1. Attachment: viruses attach to the cell membrane 2. Entry by receptor-mediated endocytosis or fusion 3. Uncoating by viral or host enzymes 4. Biosynthesis: production of nucleic acid and proteins 5. Maturation: nucleic acid and capsid proteins assemble 6. Release by budding (enveloped viruses) or rupture

How can prion diseases be acquired/transmitted?

Inherited and transmissible by ingestion, transplant, and surgical instruments

Analyze the graph comparing acute, persistent, and latent infections

Latent virus remains in asymptomatic host cell for long periods May reactivate due to changes in immunity A persistent viral infection occurs gradually over a long period; is generally fatal

What is the significance of lysogeny?

Specialized transduction Specific bacterial genes transferred to another bacterium via a phage Changes genetic properties of the bacteria

What diseases are caused by prions?

Spongiform encephalopathies: "Mad cow disease" Creutzfeldt-Jakob disease (CJD) Gerstmann-Sträussler-Scheinker syndrome Fatal familial insomnia Sheep scrapie

What is found in all viruses?

Virion—complete, fully developed viral particle Nucleic acid—DNA or RNA can be single- or double-stranded; linear or circular Capsid—protein coat made of capsomeres (subunits)

What are viruses made out of ?

Virion—complete, fully developed viral particle Nucleic acid—DNA or RNA can be single- or double-stranded; linear or circular Capsid—protein coat made of capsomeres (subunits) *Enveloped Viruses contain* Envelope—lipid, protein, and carbohydrate coating on some viruses Spikes—projections from outer surface

Characteristics of Viroids

Viroid= small, short pieces of circular naked RNA ; does NOT have protein coat; infects PLANTS mainly

Define the nature of a virus and explain how a virus differs from a cell.

Viruses contain Obligatory intracellular parasites Require living host cells to multiply Contain DNA or RNA Contain a protein coat No ribosomes No ATP-generating mechanism

How are viruses are cultured?

Viruses must be grown in living cells Bacteriophages are grown in bacteria Bacteriophages form plaques, which are clearings on a lawn of bacteria on the surface of agar Each plaque corresponds to a single virus; can be expressed as plaque-forming units (PFU) In living animals In embryonated eggs Virus injected into the egg In cell cultures Tissues are treated with enzymes to separate cells Virally infected cells are detected via their deterioration, known as the cytopathic effect (CPE) Continuous cell lines are used