W hole Virsuses

Virus taxonomy is regulated by what organization?

International Committee on Taxonomy of Viruses (ICTV)

What characteristics are used to classify viruses?

Nucleic acid type, envelope presence, capsid symmetry, virion dimensions

What does the Baltimore Classification System focus on?

Viral genome type and how viral mRNA is produced

Class I viruses

dsDNA viruses

Class II viruses

ssDNA viruses

Class III viruses

dsRNA viruses

Class IV viruses

Positive-sense ssRNA viruses

Class V viruses

Negative-sense ssRNA viruses

Class VI viruses

Retroviruses (+ssRNA with reverse transcription)

Class VII viruses

Hepadnaviruses (DNA viruses that use reverse transcription)

What is positive-sense RNA?

RNA that can function directly as mRNA

What is negative-sense RNA?

RNA that must first be transcribed into positive-sense RNA

What enzyme must negative-sense RNA viruses bring into the host cell?

RNA-dependent RNA polymerase

What is the difference between enveloped and nonenveloped viruses?

Enveloped viruses bud from host membranes; nonenveloped viruses usually leave by lysis

How do nonenveloped viruses leave host cells?

Lysis of the host cell

How do enveloped viruses leave host cells?

Budding through host membranes

What is a virion?

A complete infectious virus particle

What is viral tropism?

The preference of a virus for specific host cells or tissues

Why do viruses bind specific host receptors?

To attach and gain entry into susceptible cells

What are the major outcomes of animal virus infection?

Lysis, persistent infection, latent infection, transformation

What is a lytic infection?

Virus replication followed by host cell death

What is a persistent infection?

Continuous virus production without immediate cell death

What is a latent infection?

Virus remains dormant and can reactivate later

What is viral transformation?

Conversion of normal cells into tumor cells

How are bacteriophages cultivated?

In actively growing bacterial cultures

What is a viral plaque?

A clear area of cell destruction caused by viral replication

What are cytopathic effects (CPEs)?

Visible changes or damage in infected cells

What are prions?

Infectious proteins lacking nucleic acids

What diseases are caused by prions?

Scrapie, BSE, CJD, kuru, fatal familial insomnia, GSS

What is the normal prion protein called?

PrPC

What is the abnormal prion protein called?

PrPSc

How do prions reproduce?

PrPSc converts normal PrPC into abnormal PrPSc

What is Chronic Wasting Disease (CWD)?

A fatal prion disease affecting deer, elk, and moose

Which virus family includes herpes simplex virus (HSV)?

Herpesviridae

Which diseases are caused by HSV and VZV?

HSV causes herpes; VZV causes chickenpox and shingles

What type of genome do herpesviruses have?

Double-stranded DNA

What is unique about herpesvirus infections?

They establish latent infections in neurons

What drug is commonly used against herpesviruses?

Acyclovir

How does acyclovir work?

It is a nucleoside analog that terminates viral DNA synthesis

What are immediate early genes in herpesvirus infection?

Genes that regulate viral replication

What are late genes in herpesvirus infection?

Genes that encode structural proteins

What is VP16 in herpesvirus infection?

A viral protein required for activation of early genes

What host factor is important for herpesvirus lytic infection?

HCF-1

Why is herpesvirus latent in neurons?

HCF-1 remains in the cytoplasm and early genes are repressed

What triggers herpesvirus reactivation?

HCF-1 enters the nucleus and VP16 is produced

What is the tegument of herpesviruses?

A protein layer between the capsid and envelope

Where is the herpesvirus envelope acquired?

Golgi apparatus or endosomes

What is the largest group of viruses?

Double-stranded DNA viruses

Name important dsDNA vertebrate viruses.

Herpesviruses and poxviruses

What human diseases are caused by poxviruses?

Smallpox

What virus causes cervical cancer and genital warts?

Human papillomavirus (HPV)

What type of genome does rotavirus have?

Double-stranded RNA

What disease is caused by rotavirus?

Severe diarrhea in children

What is the appearance of rotavirus?

Wheel-like

Is rotavirus enveloped or nonenveloped?

Nonenveloped

What is a viroplasm?

A viral inclusion body where rotavirus replication occurs

Where is the third protein layer added to rotavirus?

Endoplasmic reticulum

What type of genome do coronaviruses possess?

Positive-sense single-stranded RNA

Can positive-sense RNA genomes be translated immediately?

Yes

What enzyme do positive-sense RNA viruses synthesize?

RNA-dependent RNA polymerase

Examples of medically important positive-sense RNA viruses.

Polio, Zika, Hepatitis A, SARS-CoV, SARS-CoV-2

What receptor does SARS-CoV-2 use?

ACE2 receptor

How do coronaviruses enter cells?

Fusion after receptor attachment

Where are coronaviruses assembled?

Endoplasmic reticulum

How are coronaviruses released?

Exocytosis

What type of genome do influenza viruses possess?

Negative-sense single-stranded RNA

What family does influenza belong to?

Orthomyxoviridae

What family does rabies belong to?

Rhabdoviridae

What family does Ebola belong to?

Filoviridae

What family includes measles and mumps viruses?

Paramyxoviridae

Why must negative-sense RNA viruses carry RNA polymerase?

Their genomes cannot function directly as mRNA

What intermediate is produced during negative-sense RNA replication?

Positive-sense RNA

What type of genome does influenza have?

Segmented negative-sense RNA

How many genome segments does influenza contain?

Seven or eight

What protein mediates influenza fusion?

Hemagglutinin (HA)

What causes influenza viral fusion?

Low pH in the endosome

How does influenza acquire its envelope?

Budding from the host membrane

What is antigenic drift?

Small gradual mutations in viral antigens over time

What is the result of antigenic drift?

New strains that may escape existing immunity

Why is a new flu vaccine needed each year?

Antigenic drift

What is antigenic shift?

A major genetic reassortment event creating a new influenza strain

What causes antigenic shift?

Mixing of genome segments from different influenza viruses

Which animals are often involved in antigenic shift?

Pigs

What pandemic was caused by antigenic shift in 2009?

H1N1 swine flu

What two proteins define influenza A subtypes?

Hemagglutinin (H) and neuraminidase (N)

What does H1N1 mean?

Hemagglutinin type 1 and neuraminidase type 1

How many hemagglutinin subtypes exist?

18

How many neuraminidase subtypes exist?

11

What is a retrovirus?

An RNA virus that converts RNA into DNA

What enzyme is required by retroviruses?

Reverse transcriptase

What is a provirus?

Viral DNA integrated into the host genome

What virus is the most important retrovirus in humans?

HIV

What are the three major enzymes of HIV?

Reverse transcriptase, integrase, protease

What does HIV integrase do?

Inserts viral DNA into the host chromosome

What does HIV protease do?

Matures viral proteins into infectious particles

What receptor does HIV bind?

CD4

What is reverse transcription?

Synthesis of DNA from an RNA template

What type of virus is Hepatitis B virus?

A DNA virus that uses reverse transcription

What family does Hepatitis B belong to?

Hepadnaviridae