Viruses - structure and pathophysiology

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

What is the function of a Capsid?

• Nucleocapsid:

• Capsomeres

• What viruses are made of a nucleocapsid?

Viral Envelope:

• Where do they bud/pinch off from?

surrounds/protects viral genome from host defenses

• capsid + nucleic acid(genome)

• protein subunits

• “Naked viruses”

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

Attaches onto receptors on host cell membranes, enhancing spread/transmission to infect others

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

2. 3D, 20 sided figure (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/Uncoating: the host membrane is penetrated by whole virus or nucleic acid and enzymes break down capsid to uncoat virus and engulf it

3. Synthesis: replication and protein prooduction

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

5. 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 that a virus can infect

• 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 replicated at?

Where do RNA viruses replicated and assembled at?

How do retroviruses life cycle look?

the host cells 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