Chapter 5: Viral Structure and Function

virus

genetic element that can multiply only in a living (host) cell

Are viruses living?

no, not found on tree of life

Why are viruses called obligate intracellular parasites?

lives in the cell and needs host cell for energy, metabolic intermediates, and protein synthesis

Viruses have their own…

nucleid acid genome

virus particle (virion)

extracellular form of a virus that exists outside host and facilitates transmission from one host cell to another

Replication/reproduction of viruses occurs only upon…

infection (entry into host cell)

What are the different varieties in features of viruses?

• DNA or RNA genomes

• ss or ds

• size

• shape

What is the difference between a naked virus and an enveloped virus?

naked virus has no envelope

What are 3 enzymes inside virions?

1. lysozymes

2. neuraminidases

3. nucleic acid polymerases

What are the functions of lysozymes in virions?

• makes a hole in the cell wall to allow nucleic acid entry

• lyses bacterial cell to release new virions

What are the functions of neurominidases in virions?

• destroy glycoproteins and glycolipids

• allows liberation of viruses from cell

What are the 2 nucleic acid polymerases in virions?

1. RNA replicases

2. reverse transcriptase

RNA replicases

RNA-dependent RNA polymerases

reverse transcriptases

RNA-dependent DNA polymerase in retroviruses

What kind of virus is the easiest to grow and how do you grow them?

bacterial viruses;

hosts in liquid medium or spread as “lawns” on agar and inoculated with virus

What are animal and plant viruses cultivated in?

tissue cultures from animal organ in culture medium or hairy root based system in liquid medium

What is the major difference between prokaryotic and eukaryotic viruses?

nucleid acid entry in prokaryotes and virion entry in eukaryotes

What are the 5 steps of viral replication in a permissive (supportive) host?

1. attachment

2. penetration

3. synthesis

4. assembly

5. release

What is the lytic replication cycle of bacteriophages?

1. attachment to the cell wall and adsorption of phage virion

2. penetration of viral nucleic acid

3. synthesis of viral nucleic acid and protein in the cytoplasm

4. assembly and packaging of new viruses in the cytoplasm

5. cell lysis and release of new virions

What is the lysogenic replication cycle of bacteriophages?

1. attachment to the cell wall and adsorption of phage virion

2. penetration of viral nucleic acid

3. viral DNA is integrated into host DNA

4. viral DNA is replicated with host DNA at cell division

What is the replication cycle of animal viruses?

1. attachment to the host cell membrane by binding spikes to cell receptors

2. penetration of virus via endocytosis or fusion

3. synthesis of new viruses in the nucleus/golgi/cytoplasm

4. assembly of viral spike proteins into the cell membranes and the viral envelope and the nucleocapsid is formed

5. release via budding off or exocytosis

What is the difference between replication processes of bacteriophages and animal viruses in terms of attachment?

bacteriophages → cell wall

animal viruses → membrane & receptors

What is the difference between replication processes of bacteriophages and animal viruses in terms of entry?

bacteriophages → viral DNA/RNA enters

animal viruses → endocytosis or fusion

What is the difference between replication processes of bacteriophages and animal viruses in terms of synthesis/assembly?

bacteriophages → cytoplasm

animal viruses → nucleus/golgi/cytoplasm

What is the difference between replication processes of bacteriophages and animal viruses in terms of release?

bacteriophages → lysis or lysogeny

animal viruses → budding off or exocytosis