Micro - ch. 13 - Viruses, viroids, prions

virus

obligate intracellular parasite that infects all 5 kingdoms

• nucleic acid (DNA/RNA) core and protein coat

• has lipid envelope and other attachments

virion

complete virus OUTSIDE the cell

capsid

protein coat surrounding/protecting viral genetic material

spikes 

carb/protein projections which specifically match receptors to hosts cells

host range

types of cells microbe can infect

shapes of viruses

helical, polyhedral, enveloped, complex

helical

long tubular rods, rigid or flexible

polyhedral

many sides 

enveloped

surrounded by lipid membrane, spiked

complex

contain extra structures like tails, fibers - common in bacteriophages “steam punk octopus” 

enveloped viruses

fuse to host cell membrane

• easier entry 

• mimic host membrane (invade immune system)

• surface proteins evolve rapidly 

What are the ways to grow viruses?

1. in bacteria

2. in living animals

3. chicken eggs

4. tissue culture

Why do we need to grow viruses?

for prevention or tests

What are ways to identify viruses?

• with antibodies

• by DNA sequencing

• with electron microscope

What are the types of bacteriophage reproduction?

bacteriophage LYTIC cycle

Lysogenic cycle

What happens in attachment phase of lytic cycle?

virus binds to bacterial wall and spikes bind to their specific receptors on the host cell membrane

describe the penetration/entry phase of lytic cycle?

lysozymes are released to break a hole in bacterium

• designed to break down peptidoglycan

what happens in the injection phase of lytic cycle?

viral nucleic acid (DNA/RNA) is injected into host

describe what happens in biosynthesis phase of lytic cycle

viral genes take over the host cell and force it to make viral nucleic acid and protein coats 

• hijacking cell

what happens in the assembly phase of lytic cycle?

newly synthesized viral pieces into new viruses

describe the last phase of the lytic cycle; lysis/release

host cell bursts (lyses) and release new viruses which infect other cells

what is the lysogenic cycles main defense?

“hide” and “wait” strategy rather than immediate multiplication and cell lyses

What happens in attachment phase of lysogenic cycle?

virus attaches to host cells surface

what happens in the penetration phase of lysogenic cycle?

virus injects DNA into host cell

what happens in the integration phase of lysogenic cycle?

DNA inserts itself into the host cell and become prophage (hidden/dorment viral DNA)

What happens in replication of lysogenic cycle?

the viral DNA stays inactive inside the hosts DNA and the host cells lives and divides normally copying the viral DNA each time 

what happens in activation of lysogenic cycle?

something (stress/UV light) triggers and viral DNA to removes itself from host DNA and enter lytic cycle 

What happens in the attachment of animal virus life cycle?

virus attaches to specific receptors (proteins) on animal cell membrane

describe the entry phase of the animal virus life cycle

entire virus is engulfed by endocytosis (solid particle is swallowed) or membrane fusion (enveloped viruses) 

what happens in the uncoating phase of the animal virus life cycle?

once inside, the virus removes the capsid releasing viral nucleic acid into host cell

what happens in the biosynthesis phase of the animal virus life cycle?

viral RNA enter the nucleus where it is replicated by viral RNA polymerase (synthesized)

What happens in the assembly phase of the animal virus life cycle?

new virus particles are assembled

What are the 3 different phases the last stage of the animal virus life cycle goes through?

1. break through membrane

2. insert into host DNA (provirus)

3. bud off host membrane around it

What happens in the 2nd phase in the last stage of animal virus life cycle?

it can either:

• stay dormant

• break open the cell (restart)

• form a tumor (cancer)

Inclusion body

abnormal clump of material inside a cell → during viral infections or sometimes seen in cancerous / stressed cells 

Polykaryocytes

several cells fused together, often caused by viral infection or cancerous mutation

**multiple nuclei per cell

oncogenes

genes that can cause cancer when they are mutated or overactive

“genetics loads the gun - lifestyle pulls the trigger”

oncoviruses

certain virus can insert genes into host DNA and disrupt normal cells

• lead to uncontrolled cell growth → start tumor 

cancer

cell grows and divides uncontrollably and ignored normal signals that tell them to stop

Papovaviruses

split into papillomaviridae (HPV) and polyomaviridae (JCvirus)

What is HPV?

• human papillomavirus

group of 150 related DNA viruses

causes warts

high risk HPV that infect the genital area and cause cancer (cervical cancer) 

most common STI

adenoviruses

DNA virus

respiratory infections

common cold

conjunctivitis (pink eye)

stomach flu

herpes virus

family of enveloped DNA viruses

lifelong infections that are latents (inactive) in the body and active later

• cold sore, chicken pox → shingles, herpes STI

pox

enveloped DNA virus

• small pox, cow pox, monkey pox, chicken pox

Picornaviruses

“pico” - small “rna” - RNA virus

non enveloped

polio, hand foot mouth disease, common cold 

Togaviruses 

RNA viruses, enveloped

“toga” - cloak

causes encephalitis (inflammation of brain), German measles

Orthomyxoviruses

enveloped RNA virus

causes influenza A-D

Paramyxoviruses

enveloped RNA

measles, mumps, croup

MMR vaccine (measles, mumps, rubella) 

Rhabdoviruses

enveloped RNA viruses

distinct bullet shape

rabies**

Retroviruses

enveloped RNA viruses

causes HIV → AIDS and HTLV like leukemia and lymphoma

DNA oncogenic viruses

have the ability to cause cancer

Epstein-Barr virus (EBV)

enveloped DNA virus

mononucleosis “mono”

Burkitts and Hodgkisn 

Burkitts 

cancer of B lymphocytes (WBC)

fast growing tumor (aggressive)

grows in jaw or ABD

Hodgkins 

cancer of lymphatic system

treatment is successful

Acute infection

short term infection normally cleared by immune system with days to weeks 

Chronic infection

long term infection where pathogen persists body (up to life time) because it invades or suppresses immune system

latent viral infection

remains in host for long time without disease or symptoms but can be reactive

Prion disease

! not a virus !

misfolded, infectious protein, triggers normal proteins in the brain to misfold

• mad cow disease, kuru, scrapie

viroids 

smallest known infectious agents thats simpler than viruses → infects plants

• pieces of circular RNA without protein coat → disease cause by interfering with normal gene expression 

Oncolytic virus

virus that infects/destroys cancer cells while sparing normal healthy cells

• can be naturally occurring or genetically modified