Viruses and Viroids

Virion

Metabolically inert (inactive), extracellular virus particle, not considered living organism

what happens when a virion enters a host

viral nucleic acids become active and viral multiplication results THEREFORE VIRUSES ARE ALIVE WHEN MULTIPLY IN A HOST

Obligatory intracellular parasites

require living host cells in order to multiply

What can viruses do nor not do

DNA or RNA, surrounded by protein coat (capsid), no ribosomes, no plasma membrane, no binary fission, can pass through bacteriological filters (WAYYY SMALLER THAN BACTERIA)

What do viruses lack?

enzymes for protein synthesis for ATP generation thus they take over metabolic machinery of a host cell

Viruses may be

an agent of disease, agent of heredity (permanent genetic change which may be harmful, have no effect, or provide beneficial effects

what are we all infected with?

Herpes virus, over 90% of U.S. population has one or both of HSV-1 and HSV 2

ever had chicken pox?

still have varicella-ZosterVirus

What is the Tobacco Mosaic virus

Adolf Mayer demonstrated TMV could be transmitted form plant to plant,

who is dimitri iwanowski

the man who attempted to filter out the infectious agent in TMV plants, found that sap from infected plants was filtered through a porcelain filter, filtered sap was still infectious

first disease caused by a filterable agent

Yellow fever

Host range

spectrum of host cells the virus can infect

why can viruses only able to infect specific types

match up with specific host species, and only sometimes cross host species barrier thus expanding host range

- human specific

- animal specific

bacteriophage (phage)

viruses that infect bacteria

phages are a major component of the human virome why is this important?

enemy of my enemy, phage therapy uses phages to treat bacterial infections

steps to viral infection

Influenza virus becomes attached to a target epithelial cell

The cell engulfs the virus by endocytosis

Viral contents are released, Viral RNA enters the nucleus where it is replicated by the viral RNA polymerase

Viral mRNA is used to make viral proteins

New Viral particles are made and released into the extracellular fluid the cell, which is not killed in the process, continues to make new virus

characteristics of living organisms

- Responsiveness

- Order

- Growth

- Metabolism

- Energy transformation

- Reproduction

- Made of cells

Viruses components

2 components: capsid and genetic material

why are viruses not living

cannot carry out life processes (metabolism, reproduction) without a host

Cells components

genetic material and the other "stuff" that lets them make proteins

What is a virion

complete fully developed infectious viral particle composed of nucleic acid and surrounded by a protein coat

RNA

single- stranded, instead of thymine they have uracil

DNA

double stranded, instead of uracil they have thymine

Viruses can either be DNA or RNA but

NEVER BOTH, they can have

ssRNA( single-stranded)

dsRNA (double-stranded)

ssDNA (single-stranded)

dsDNA (double-stranded)

Which type of virus infect every type of organism

viruses with ALL types of nucleic acids eg Retroviruses which has only been found in animals

retroviruses have rna and insert into the host genome (ssRNA)

3 shapes of viruses

helical, polyhedral, complex

what is viral capsid made up of

capsomeres

functions of capsids

Protection from environment

Facilitate interaction with host cell

Assist in movement between cells in multicellular organisms

Facilitate vector-mediated transmission between organisms

enveloped virus

membrane derived from portions of host cell membranes

purpose of envelope

Helps them attach to host cells

May help them avoid immune system

The membranous envelope sensitive to desiccation, heat, and detergents = easier to kill than non-enveloped viruses

EX: herpesviruses, Hepatitis D, Retroviruses (HIV)

nonenveloped helical virus

capsid is resistant to disinfectants and solvents

Norovirus: high resistance and can remain infective for several months in environment

which is more resistant to disinfectants non-enveloped or enveloped

non-enveloped

viral classification

Not very standardized

Often named for host or appearance or disease

Usually grouped by structure, chemical composition, and genetic similarities

Virus families end in -viridae

Viral genera usually end in -virus

what is HPC

human papilloma (warts) virus

what is HIV

human immunodeficiency virus

ranavirus

Virus that infects fish, amphibians, reptiles (Rana is latin for frog; it was first discovered in a frog)

zoonosis

an infectious disease transmitted between species from animals to humans (or vice versa)

antigenic shift

animal pathogens undergoes genetic change in an intermediate host and can infect humans

how to quantify viruses

plaque assay

what is plaque assay

Virus Determine number of infectious units per volume of fluid

Mix dilution of virus with enough bacterial cells that a lawn of cells form

Count zones of lysis clear zones caused by virus bursting or lysing cells) = plaque

Assume each plaque originated from 1 virus

lytic cycle of bacteriophage

Phage attaches to host cell and injects DNA

Phage DNA circularizes and enters lytic cycle or lysogenic cycle

New phage DNA and proteins are synthesized and assembled into virions

Cell lyses, releasing phage virions

lysogenic cycle of bacteriophage

Phage attaches to host cell and injects DNA

Phage DNA circularizes and enters lytic cycle or lysogenic cycle

Phage DNA integrates within the bacterial chromosome by recombination becoming a prophage

Cell undergoes binary fission

what does lytic cycle end with

lysis

what does lysogenic cycle end with

host cell remains alive, lysogenic cells immune to reinfection by same phage

phage conversion

cells ma have new properties (produce a toxin)

transformation

Some viruses can cause our cells to become cancerous (HPV)

lysis

Multiplication if virus causes cell death and release of virus (Influenza)

persistent

slow release of virus without cell death (rare form of encephalitis)

latent

Virus lays dormant until activated by a stimulus (herpesvirus that causes chickenpox)

tumor viruses

Virus makes proteins that interfere with cell functions that would normally prevent excessive growth

Example: HPV

Group of more than 200 related viruses

40+ spread through sexual contact

Low risk: non cancerous

High risk: cancerous ( about 12 types)

low risk

most high-risk infections are

asymptomatic and go away within 1-2 years. Some can persist for many years through - cancer risk higher

plant disease and viroid's how to infect plants?

remember plant cells have cell wall therefore protection

- viruses must enter through wounds or be assisted by plant parasites

plant viroids

short pieces of naked RNA, replicated continuously by host range RNA polymerase

RNA does not code for any proteins through

may cause disease by gene silencing

prion

infectious agent consisting of a self replicating protein, with no detectable nucleic acid (mad cow disease)

Diseases caused by conversion of normal host glycoprotein called Prpc (located on chromosome 20) into infectious form called PrPsc

chronic wastings disease

Affects deer, elk, and moose (not a huge % of population)

Caused by prions

Transmission can occur through direct contact and environmental

So far no evidence that it can be transmitted to humans but CDC recommends not consuming meat from infected animal