Introduction to Virology and Viral Replication

Flashcards covering virus characteristics, theories of origin, morphologies, structure, classification, replication cycles, and bacteriophage interactions based on lecture notes.

How is the organization of viruses characterized compared to cellular organisms?

Viruses have simple organization, while cellular organisms have complex organization.

What can be the genome type of a virus?

DNA or RNA genome.

Can viruses reproduce outside of living cells?

No, they are unable to reproduce outside of living cells.

What term describes the lifestyle of viruses as parasites?

Obligate intracellular parasites.

What are the genome and reproductive characteristics of cellular organisms?

They have a DNA genome and RNAs, and they carry out cell division.

According to the theory of reductive origin, how did viruses evolve?

By degenerative evolution from intracellular parasitic cells.

What does the theory of intracellular origin suggest about viral evolution?

Viruses evolved from functional parts of cells that acquired an ability to reproduce themselves uncontrolled by the cell.

What does the theory of independent origin hold regarding viral evolution?

Viroid nucleic acids could have evolved outside of cells during the "RNA world" and acquired the ability to infect cells.

What are the dimensions of the Tobacco mosaic virus?

$15 \times 300\,nm$.

How does Pandoravirus compare to other known viruses and bacteria?

It is bigger by far than any other known virus and rivals bacteria.

What is the length of the Ebola virus?

$970\,nm$.

What are the dimensions of the Smallpox virus?

$200 \times 300\,nm$.

What defines multicomponent virus genomes?

The genomes are segmented and the segments are distributed into separate viral particles.

What is required for a multicomponent virus to successfully cause infection?

Multiple distinct particles are required.

What does the cultivation of viruses require?

Inoculation of a living host cell.

What are the common hosts used for virus cultivation?

Suitable animals, embryonated eggs, and tissue (cell) cultures.

What are plaques in the context of tissue culture?

Localized areas of cellular destruction and lysis.

What are cytopathic effects (CPEs)?

Microscopic or macroscopic degenerative changes or abnormalities in host cells and tissues.

Which cavities or sacs in an egg are used for virus inoculation?

Amniotic cavity, Allantoic cavity, Yolk sac, and Chorioallantoic membrane.

In viral structure, what is the Delivery system?

Structural components that enable the virus to survive and bind host cells.

In viral structure, what is the Payload?

The viral genome and enzymes required for the initial steps of replication.

Which virus is used as an example for icosahedral capsid symmetry?

Herpes simplex 1 (HSV-1).

What types of rotation axes are included in icosahedral symmetry?

Fivefold, threefold, and twofold axes.

What is the state of DNA within the icosahedral capsid of herpes?

Spooled DNA.

What is the head dimension of Phage T4?

$100\,nm$.

What is the total length of a Phage T4 particle?

$300\,nm$.

What is the function of the tail fibers in Phage T4?

They facilitate attachment to the surface of the host cell.

What happens after Phage T4 attaches to a cell?

The sheath contracts and the core penetrates the cell surface, injecting the phage genome.

What is contained inside the helical filament of the Tobacco mosaic virus (TMV)?

A single-stranded RNA genome coiled inside.

Provide an example of a filamentous bacteriophage.

Bacteriophage M13.

What components make up an enveloped virus?

Nucleocapsid, lipid bilayer envelope, and glycoprotein spikes.

What is the tegument in a herpes virion?

Proteins surrounding the capsid, located between the capsid and the envelope.

Which virus is characterized as an asymmetrical virus?

Vaccinia poxvirus.

How is the DNA genome of a pox virion stabilized?

By a hairpin loop at each end.

What properties are used of classify viruses?

Type and structure of nucleic acid, presence or absence of envelope, type of capsid symmetry, and replication strategy.

What do scientists call the collection of diverse viruses found in and on the human body?

The Human Virome.

Name four locations in the body where the human virome is found.

Blood, Skin, Respiratory system, and Gut.

Which viral family in the human virome exhibits low genetic diversity and is primarily pathogenic?

Adenoviridae.

What are the five general steps of virus replication?

Adsorption, penetration and uncoating, synthesis of viral proteins and nucleic acids, assembly of virions, and release.

What mediates the adsorption of virions to host cells?

Viral surface proteins and/or enzymes mediate attachment to specific host receptors.

What does HSPG stand for in the context of viral receptors?

Heparin sulfate chains of proteoglycans.

What is the host receptor for the Epstein-Barr virus?

Receptor for the C3d complement protein on human B lymphocytes.

What receptor does HIV use on T-helper cells?

CD4 protein.

What are the co-receptors used by HIV?

CXCR-4 or the CCR5 receptor.

What is the receptor for Influenza A virus?

Sialic acid-containing glycoprotein.

Which receptor is used by the Measles virus?

CD46 complement regulator protein.

What is the cell surface protein receptor for the Rabies virus?

Acetylcholine receptor on neurons.

What are the receptors for Rhinovirus on respiratory epithelial cells?

Intercellular adhesion molecules (ICAMs).

What is the receptor for Vaccinia virus?

Epidermal growth factor receptor.

What are the three mechanisms of viral penetration and uncoating?

Injection of nucleic acid, fusion of envelope with host membrane, and endocytosis.

How do naked viruses typically achieve penetration?

Direct penetration.

What structures are involved in the entry of an enveloped virus by endocytosis?

Clathrin-coated pit, coated vesicle, and endosome.

Which enzyme is used by retroviruses like HIV for synthesis?

Viral reverse transcriptase.

Which enzyme is used by single-stranded +RNA viruses for genome replication?

Viral RNA polymerase.

Which viruses use a host RNA polymerase for mRNA synthesis according to the synthesis table?

Double-stranded DNA viruses and Single-stranded DNA viruses.

What genes encode capsid proteins?

Late genes.

How are naked viruses typically assembled?

Empty procapsids are formed, and then the nucleic acid is inserted.

Where do Adenoviruses replicate their nucleic acid and assemble their capsids?

The Nucleus.

Where does nucleic acid replication occur for Hepadnaviruses?

The Cytoplasm.

What membrane is used in budding for Coronaviruses?

Golgi apparatus and endoplasmic reticulum.

Where does capsid assembly occur for Orthomyxoviruses?

The Cytoplasm.

How are naked viruses usually released from the host cell?

By lysis of the host cell.

How do enveloped viruses typically release from the host cell?

By budding outward, surrounded by a modified host membrane.

In the virus replication cycle, what is the "Eclipse" period?

The time during which the virus has disassembled and is replicating, but new virions have not yet been assembled.

What is the typical transcription pattern for a DNA virus?

Early genes, then DNA replication, then late genes.

What characterizes an acute infection?

A rapid increase in the relative amount of virus followed by rapid clearance.

What defines a latent infection?

The virus remains in the tissues for long periods with very low or no detection before potentially reactivating.

What characterizes a chronic infection?

The virus is continuously produced and present in tissues over months or years.

Which Salmonella host molecules can serve as phage receptors?

LPS components, membrane proteins (OmpF and TolC), and flagellar proteins.

What is the "ghost" in Phage T4 DNA insertion?

The empty capsid that remains outside the bacterium after the DNA is injected.

What happens during the lytic cycle of a bacteriophage?

The phage genome reproduces progeny particles and then lyses the cell to release them.

What happens during lysogeny in Phage Lambda?

The phage genome integrates itself into the host genome as a prophage and replicates with it.

What enzyme directs the excision of a phage chromosome from the host genome?

Site-specific DNA recombinase.

Which prophage gene provides the Botulinum toxin trait to Clostridium botulinum?

Phage C1.

Which prophage gene is responsible for the Shiga toxin (stx) in E. coli O157:H7?

Phage 933.

What human protein provided by HERV-W is essential for placental fusion?

Syncytin-1.

What is a slow-release replication cycle?

A cycle where a filamentous phage produces particles and exits without lysing the cell, though host growth slows.

What are restriction endonucleases?

Bacterial enzymes that cut invading DNA.

What is CRISPR in the context of bacterial defense?

A bacterial immune system.