Chapter 18 Studying Viruses and Prokaryotes https://www.youtube.com/watch?v=UEKS4w9bfJg

Infections can be caused in several ways.

Viruses, bacteria, viroids, and prions can all cause infection. Any disease-causing agent is called a pathogen. 1 nanometer (nm) = one billionth of a meter 100 nm eukaryotics cells 10,000-100,000 nm viroids 5-150 nm viruses 50-200 nm prokaryotics cells 200-10,000 nm prion 2-10 nm

Bacteria: one-celled, no nucleus, prokaryotic Viruses: has DNA/RNA and protein coat cannot reproduce on their own smaller Both: Can cause infections Respond to the environment Have genes, can reproduce

Comparison of viruses, viroids, and prions Virus: 50 – 200 nm Made of a protein coat (capsid) and genetic material Viroid: 5 – 150 nm Made of a single-stranded RNA molecule, NO protein coat Causes plant diseases (stunts growth) Prion: 2 – 10 nm Made of a misfolded protein Causes diseases of the brain (ex- Mad Cow)

Viroids – pieces of RNA

A prion is made only of proteins. causes misfolding of other proteins results in diseases of the brain

Mad Cow disease causes holes in brain tissue.

VIRUSES

What is a virus? A virus is a submicroscopic infectious particle composed of a protein coat (capsid) and a nucleic acid core. Viruses are similar in size to a large protein macromolecule, generally smaller than 200 nm in diameter.

Viruses are not considered living because they Need a host cell to reproduce Have no metabolism

Tree of Life

No links to other forms of life.

Viruses are classified by: the type of nucleic acid they contain - DNA, RNA, RNA retroviruses the shape of their protein capsule - helical, polyhedral, enveloped

polyhedral (foot-and-mouth enveloped (influenza) Different shapes of viruses polyhedral (foot-and-mouth disease) enveloped (influenza) helical (rabies) capsid nucleic acid lipid envelope surface proteins capsid surface proteins nucleic acid capsid nucleic acid lipid envelope Surface proteins

Helical Viruses ex - rabies

Polyhedral shaped cold viruses, foot and mouth disease viruses

Enveloped ex – flu virus Three parts: Capsid Genetic material Lipid envelope nucleic acid capsid lipid envelope

Bacteriophages – attack bacteria They have tails and spikes to attach to the host cells. The tail releases enzymes.

bacteriophages pierce host cells colored SEM; magnifications: large photo 25,000; inset 38,000x

Retroviruses RNA viruses that take their RNA and use the host cell’s enzymes to make viral DNA.

Retroviruses go backwards… RNA to DNA then to proteins

Viruses identify their hosts by receptors (surface proteins)

How do viruses enter eukaryotic host cells? By endocytosis Fuse with the cell membrane (HIV)

How viruses replicate

In the lytic cycle, the virus destroys the host cell.

In the lysogenic cycle, viral DNA becomes part of the host cell’s DNA. PROPHAGE – name of incorporated viral DNA.

Viral Reproduction Both: Cause infections Enter cell/ disrupt DNA Both use host cell’s materials Viral Reproduction

How viruses get into the body Cuts and scrapes Body opening and mucous membranes Viruses trick cells into letting them in by using their surface proteins Antibiotics are not effective against viruses!

Viral Treatment??? Difficult since viruses mutate, particularly their surface proteins can be altered Hybrid Medical Animation | Animation | Antigenic Shift - the Spread of a New, Mutated Virus HIV virus destroys white blood cells used in immunity!

How do vaccines work? Stimulate the body to produce antibodies (proteins that attack foreign invaders).

First viral vaccine Edward Jenner made a vaccine against small pox using cow pox.

Jonas Salk made a vaccine against polio He killed the polio virus with formaldehyde when he made the vaccine.

Vaccines stimulate the body’s immune system and it “remembers” the pathogen when encounted again.

Viral Diseases Chicken pox mumps WEST NILE

1918 Flu Epidemic

H1N1 Swine Flu

Ebola Virus

And now….the Zika virus http://abcnews.go.com/Nightline/video/zika-virus-outbreak-inside-hot-zone-36706014 http://www.cnn.com/videos/world/2015/12/22/what-is-the-zika-virus-darlington-orig-sdg.cnn/video/playlists/diseases-and-viruses/ shorter

Will they take us out?

Virus Modeling