Viruses

Virology:

T/F: viruses infect every type of cell

Who was the first ti use the word “virus” meaning poison in Latin

Whats the best way to describe viruses instead of just saying it is “non-living”

• the study of viruses

• True

• Pasteur

• active or inactive because it can direct cells to do things

Whats make a virus ACTIVE?

What makes a virus INACTIVE?

Dormant/latent virus

Genome:

It can replicate, be infectious, be transmitted, and you can get signs/symptoms

It cant replicate(damaged), non infectious, outside of host cell, doesn’t spread and not that much sign/symptom

inside host but hiding (inactive)

total of genetic info carried by orgranism

• Breakdown the term Obligate Intracellular parasites

• What is the nucleic acid made of in viruses?

• dsDNA

• ssDNA

• ssRNA

• dsRNA

Obligate : completely dependent in finding host

Intracellular: must get inside the cells of a living host

Parasite: steals host nutrients so it can grow and thrive

DNA OR RNA, but not both

• double stranded

• single stranted

• single stranded

• double stranded

Whats the smallest infectious agents?

• smallest virus?

• largest virus?

Basic structure of a Virus:

virus

• parvoviruses

• herpes simplex

1. Genetic core (genome;DNA/RNA)

2. Capsid (external coat around the DNA/RNA core)

3. 1-2 viral enzymes

4. Spike proteins

Capsid?

• Nucleocapsid:

• Capsomeres

• A naked virus only has a….

Viral Envelope:

• Where do they bud/pinch off from?

the protein shell around the nucleic acid core of a virus protects it from host defenses

• capsid + nucleic acid(genome)

• capsid subunits

• “nucleocapsid

some virus develop bilayer lipid membrane that is stolen from host cell

• Cell membrane

• Nuclear envelope

• ER

Function of Spike proteins:

Different Viral Capsid Shapes;

1. Helical:

2. Icosahedral

3. Complex

Protude from envelope, enhancing spread/transmission to infect others

1. long tube with DNA/RNA in the middle of it

2. 20-sided figure with 12 evenly spaced corners (golf ball)

3. only attack other kinds of microbes; spider shaped w/ big head

The # of genes in virus is small, why?

Enzymes that virus carry with them:

1. Polymerases:

2. Replicases:

3. Reverse transcriptase:

Some viruses carry away substances from their host:

1. Arenaviruses:

2. Retroviruses:

only have genes needed to invade host cells and redirect their activity

1. synthesize DNA and RNA

2. copy RNA

3. synthesizes DNA from RNA

1. pack along host ribosomes

2. borrow the host tRNA molecules

Growth cycle of human viruses:

• average time of cycle?

1. Adsorption - virus invade and adsorbs to receptor sites on membrane

2. Penetration- dissolving the envelope and capsid to release the viral nucleic acid

3. Uncoating: the host membrane is penetrated by whole virus and enzymes break down capsid to uncoat virus and engulf it

4. Synthesis: replication and protein production

5. Assembly: mature virus particles are constructed from growing pool of parts

6. Release: newly assembled virus leave the host

8-36 hours

“wheres & whens of adsorption”

Host range(examples):

• Restricted:

• Moderate:

• Broad:

Tropisms:

the range of cells limited by type of host cell receptors

• Hepatitis B; only the liver cells of human

• Poliovirus; intestinal and nerve cells of humans

• Rabies; various cells of all mammals

specificities of viruses for certain tissues

Where do DNA viruses enter the host cell and multiply at?

Where do RNA viruses enter the host cell and multiply at?

How do retroviruses life cycle look?

nucleus

cytoplasm

complex; first copy their RNA genomes to then make the DNA

Describe the Early Phase and Late Phase of a DNA virus Synthesis

Early phase:

1. vDNA enter nucleus→ RNA transcript moves into cytoplasm to be translated into viral proteins (enzymes)

   The host cells DNA polymerase is involved in this phase

Late phase:

1. Parts of viral genome are translated into proteins for the capsid and the structures

2. New viral genomes and capsids are assembled

   mature viruses and released by budding

RELEASE
Cell lysis/rupture:

Budding:

• nonenveloped and complex viruses that reach maturation in the cell nucleus/ cytoplasm are released when the cell bursts open

• Enveloped viruses; binds to membrane around it and make a pouch to pinch off and release virus

Cytopathic effects:

• Inclusion bodies:

• Syncytia:

• Development of intracellular changes

• Accumulated damage from a virus infection does what?

virus-induced damage to cell that alters its microscopic appearance

• masses of viruses or damaged cell organelles in nucleus/cytoplasms “rough spots”

• many damaged host cells clumped into single large cells containing multiple nuclei (giant cells)

• kills most host cells

Example of Cytopathic effects and what happens?

1. Respiratory Syncytial Virus (RSV): a syncytium forms (giant cells)

2. Rabiesvirus: infected cells accumulate structures (Negri bodies) in their cytoplasm (Inclusion bodies)

Persistent infections:

• Provirus (example):

• Chronic latent state of a provirus(example):

The cell goes through stages 1 and 2 and is not immediately lysed (last weeks-life). Just chills around in the host and may not have any signs

• vDNA becomes incorporated into host DNA (measles virus in brain cells)

• Latent viruses become activated under the influence of stimuli like stress & other illnesses ( Herpes and chickenpox behave this way)

Bacteriophage:

• Why do we need to learn about them?

Virophages:

“bacteria-eating virus”

• some of the most deadly bacteria infections, they cause bacteria to develop new toxins that they didn’t have before

Viruses that infect other virus

T-even Bacteriophage

• what do they infect

• what shape are they?

• Destructive “life-cycle” of a T- T-bacteriophage

• Name some structures in this virus?

• E.coli

• Complex

• “lytic cycle”

• Collar, Base plate, Tail pins, Fibers, Collar, Central tube surrounded by a sheath, Isosahedral capid

Steps of T-Bacteriophages Life cycle

1. Adsorption

2. Penetration

3. Duplication of phages; Replication of virus material

4. Assembly of new virons

5. Maturation

6. Lysis of weakend cell

7. Release of viruses

What differences do the cycle of t-bacteriophages have than an animal virus life cycle?

• no uncoating step; injection of only the viral nucleic acid into the host cell

• Phages never bud out of bacterial cell

Temperate phages:

Inactive prophage state:

ungergo adsorption and penetration but bacteriophage doesnt replicate or relases lays dormant

viral Dna is entered into bacterial chromosome and copied during bacteria cell division

Lysogeny:

Induction:

• viral genome inserting into bacterial host chromosome

• prophage (bacterium) has had infection and may not remember, becomes activated and progresses directly into vReplication and lytic cycle

Lysogenic conversion:

• Examples of this

What two pathways can a temperate phage follow after entering a bacterial cell?

when a bacterium acquires a new trait from its temperate phage

• Corynebacterium diphtheriae - diphtheria toxin
  • Vibrio cholerae - cholera toxin
  • Clostridium botulinum - botulinum toxins

It can either continue with the lytic cycle or integrate into the host genome.

Helical and icosahedral are terms used to describe the shapes of a virus ______.

1. spike

2. capsomere

3. envelope

4. capsid

5. core

4

The envelope of enveloped viruses ________.

1. is identical to the host plasma membrane

2. is only composed of host endomembrane

3. does not contain spikes

4. is obtained by viral budding or exocytosis

5. None of the choices are correct

4

Which of the following is not associated with every virus?

1. Envelope

2. Capsomeres

3. Capsid

4. Nucleic acid

5. Genome

1