Chapter 6-Viruses and Prions

Question 1

Define: virus

Answer 1

-submicroscopic, infectious agents

Question 2

Define: virion

Answer 2

-single,infectious virus particle

Question 3

Define: virology

Answer 3

• the study of viruses

Question 4

Define: bacteriophage

Answer 4

-viruses that infect bacteria

Question 5

Define: pandemic

Answer 5

• worldwide outbreak of disease

Question 6

Define: Hemagglutinin

Answer 6

• glycoproteins which cause red blood cells to agglutinate or clump together

Question 7

Define: Neuraminidase

Answer 7

-an enzyme that catalyzes the breakdown of glycosides

Question 8

Define: attenuated strain

Answer 8

• genetic changes that limit infectivity

Question 9

Define: prophage

Answer 9

• in the lysogenic pathway, the result of the phage genome being incorporated into the host cells genome

Question 10

Define: provirus

Answer 10

-formed when some viruses that cause persistent infections integrate their genome into the host cell

Question 11

Define: reverse transcriptase

Answer 11

• virally encoded enzyme that enables retroviruses to use their single stranded RNA genome to direct formation of DNA

*basically special enzymes that carry out reverse transcription

Question 12

Steps of viral replication

Answer 12

Attachment: naked viruses attach to host cell membranes through capsid proteins

Penetration: enveloped viruses enter through endocytosis or membrane fusion while naked viruses enter by endocytosis

Uncoating: capsid is digested by enzymes in the endocytic vesicle or cytoplasm, or nucleus

Replication: genome is replicated and viral proteins are made

Assembly: new virions are formed

Release:

Question 13

*know table 6.1

Answer 13

Question 14

*Be able to diagram and label the parts of an enveloped and non-enveloped virus

*know the function of the parts of a virus

Answer 14

capsid: protein shell that packages and protects the genome (also accounts for the bulk of a virions mass)
capsomere: 3D subunits that account for a capsids shape
genome: entire collection of genetic material in a cell or virus
spikes: peplomers that protrude from the viral capsid or viral envelope
envelope: lipid based; surrounds the capsid

Question 15

How are viruses classified?

Answer 15

1. ) type of nucleic acid present (DNA or RNA)
2. ) capsid symmetry (helical, icosahedral, or complex)
3. ) presence or absence of an envelope
4. ) genome architecture (ssDNA, ssRNA, etc.)

Question 16

What is antigenic drift?

Answer 16

• changes to the HA and NA spikes
• minor changes
• allow the virus to evade a quick antibody response by making the new strains different enough to go unrecognized by the immune system-even if the host had a prior interaction with a related strain

Question 17

What is antigenic shift?

Answer 17

• major genetic reassortment
• broader mutations that lead to viral strains with new features, such as increased infectivity or expanded host range

Question 18

What is viral genome reassortment?

Answer 18

-when different viral strains coinfect a host cell, their genomes mix and can generate new viral combinations

Question 19

Lytic Replication (cycle)

*type of bacteriophage replication

Answer 19

-this pathway kills the host cell as newly made bacteriophages are released

Question 20

Lysogenic Replication (cycle)

*type of bacteriophage replication

Answer 20

Question 21

How is bacteriophage replication different from viral replication in animal cells?

Answer 21

• bacteriophages have a lytic or lysogenic cycle
• bacteriophages inject DNA into the host cell, while animal viruses enter via endocytosis or membrane fusion
• bacteriophages do not go through uncoating

Question 22

What is an acute infection?

Answer 22

-viruses infect a host cell and new virions are made (nonpersistant)

Question 23

What is a chronic infection?

Answer 23

• continuous release of virions over time and a slow progression of disease (persistent)
• HIV

Question 24

What is a latent viral infection?

Answer 24

• flare ups with intermittent periods of dormancy (persistent)
• herpesviridae

Question 25

How does HIV replicate in human cells?

Answer 25

Question 26

How are viruses grown in the laboratory? (Bacteriophages)

Answer 26

Plaque assays - bacteria are grown on a petri plate - phage infects cell then lyse out of the cell - infect adjacent cells - lysed cells leave a clear zone \*each plaque represents a bacteriophage **Plaque forming units: quantity of bacteriophages in an initial volume of sample** **Viral titer: quantity of virus present in a given volume of sample**

Question 27

How are viruses grown in the laboratory? (Animal Viruses)

Answer 27

- more difficult to cultivate than bacteriophages - most are grown using tissue culture techniques - live animal hosts may be used to support growth of some viruses - embryonated eggs are useful for growing certain viruses

Question 28

What is an oncogenic virus? What cancers does it cause?

Answer 28

- virus that causes cancers - cause cancer by stimulating uncontrolled host cell division and/or decreasing host cell responsiveness to death signals ex. ) - Human papilloma virus (HPV) - Human T-lymphotropic virus (HTLV)

Question 29

Agglutination Test

Answer 29

- purified antibodies linked linked to tiny latex beads - mixed with the sample - antibodies bind the viral antigen - beads agglutinate

Question 30

Latex Agglutination Test

Answer 30

- viral antigens linked to tiny latex beads - mixed with the sample - patient antibodies bind the viral antigen - beads agglutinate

Question 31

ELISA Test

Answer 31

- can be adapted to detect either antigens or antibodies in a sample (early or later infections) - target adheres to surface - change of color indicates binding

Question 32

DNA Test

Answer 32

Question 33

How do antiviral drugs work?

Answer 33

- antiviral drugs treat infections but don't typically cure them - vaccinations are an effective means for limiting infection - viruses are obligate intracellular pathogens - antivirals should be selectively toxic - viruses have fewer chemically distinct targets than living pathogens

Question 34

Antiviral Drugs

Answer 34

Drugs that block viral attachement, penetration and uncoating **Postexposure prophylaxis** - laboratory prepared mixture of injectible antibodies prevents viruses from binding and entering host cells - used directly after exposure - used to treat rabies and HIV **Docosanol** **-**blocks viral entry into host cells -used to treat cold sores caused by HHV-1 **Palivizumab** - injectable antibody preparation - blocks fusion of the respiratory syncytial virus (RSV)

Question 35

Antiviral Drugs-

Answer 35

Drugs that target viral replication, assembly, and release **Nucleoside analogs** - block replication - activated into compounds that mimic normal nucleotides - chemical dead end for nucleic acid replication ex. )Acyclovir-inhibits DNA replication of HHV-1, HHV-2 Ribavirin-targets RNA polymerases syncytial virus, hepatitis C **Nucleoside reverse transcriptase inhibitors** -targer reverse transcriptase enzymes (AZT) **Antisense antivirals** **-**short sequences of nucleotides complementary to the viral DNA - bind to viral RNA inhibiting translation - targeted RNA destroyed by cellular enzymes - ex.) Vitravene **Interferons** - signal the presence of a virus - neighboring, uninfected cells make defensive changes to limit viral entry and replication **seltamivir (Tamiflu) and zanamivir (Relenza)** -Prevent influenza A and influenza B virions from budding off the host cell surface

Question 36

What is a prion?

Answer 36

–Infectious proteins; no genetic material –Do not replicate –Cause transmissible spongiform encephalopathies (TSEs)

Question 37

Prion Infections

Answer 37

Gerstmann-Straussler-Schienker syndrome (Genetic) • Creuzfeldt-Jakob disease (CJD) – Consumption of contaminated meat • Chronic Wasting Disease- (Deer, Elk)  MT- S f Billings \>50 deer tested positive 2017  N of Chester 3 deer tested positive  Spread thru urine, saliva, central nervous system tissue, direct contact (feces?)  Not passed to humans? • Scrapie- Sheep

Question 38

How are prions spread/ treatments?

Answer 38

Death of the host occurs from nerve cell death leading to sponge-like holes in brain tissue. – Symptoms include:  dementia.  weakened muscles.  loss of balance. – This results from insoluble aggregates of abnormal prions in the brain. • The human form of TSE is called variant CJD (Creutzfeldt-Jakob disease)