Viruses

What is a virus?

Infectious particle that reproduces us using a host cell

What is a capsid?

Outer layer around nucleic acid core

What cells are capsids made of?

Capsomids

What is located in the capsid of a virus?

DNA or RNA

What is a virus capsid made of?

Protein

How do viruses reproduce?

By infecting host cells and reprogramming them

What is a viral envelope made of?

Bilayer of lipoproteins and glycoproteins

Do viruses contain enzymes?

Some

What is a viral nucleic acid?

Genetic material of a virus enclosed in a capsid

What is a viral protein?

Proteins produced by a virus serving structural roles and performing functions like attachment, replication and modulating host responses

What does virus symmetry refer to?

Geometric arrangement of protein subunits forming the capsid

What is a icosahedral virus?

Polygon with 12 corners, 20 facets and 30 edges

What shape is each facet of an icosahedral virus?

An equilateral triangle

What are the two types of icosahedrals?

Pentagon and hexagonal

What is another type of viral symmetry?

Filamentous - thin, linear, rod shaped

What shape is the head of a virus?

Icosahedral

What shape is the tail of a virus?

Filamentous

What are the four types of nucleic acid in a virus?

• Double - stranded DNA

• Double - stranded RNA

• Single - stranded DNA

• Single - stranded RNA

Does RNA or DNA viruses have a higher mutation rate?

RNA

What is viral tropism?

Ability of a given virus to productively infect a particular cell, tissue or host

What are three factors influencing tropism?

• Presence of cellular receptors - viral entry

• Availability of transcription factors involved in viral replication

• Cellular receptors of proteins found in cell or virus surface

What is the first stage of viral replication?

Absorption - attachment of virus to specific receptors of host cells

What is the second stage of viral replication?

Penetration - virus or genome enters the host cell

What is the third stage of viral replication?

Uncoating/eclipse-

• virus is not detected

• eclipse phase starts uncoating lipid membrane and protein capsid

• Becomes free; acts as template for mRNA

What is the fourth stage of viral replication?

Transcription

• mRNA code for enzyme synthesis needed for early steps in viral replication

• Virus takes advantage of existing cell structures to replicate itself

What is the fifth stage of viral replication?

Synthesis of viral components. Two types: structural and non-structural (built on ribosomes)

What is the sixth stage of viral replication?

Assembly

• Viral assembly is done by incorporating nucleic acid into capsomere

• Can occurs in host nucleus, cytoplasm or plasma membrane

What happens to the host cell as a result of lytic replication?

Host cell dies

What happens to the host cell as a result of lysogenic replication?

Host cell continues to live and function

What is viral persistence?

• Virus is not cleared but remains in specified infected cells

• May produce excessive damage silently or productively

• Example: HIV, Hep B

What is viral latency?

• Ability of a pathogenic virus’s to lie dormant in a cell as part of lysogenic viral life cycle

• A type of persistent viral infection distinguished from chronic infection