What is a virus? And is a virus alive?

TMV Tobacco Mosaic Virus- causes mosaic pattern on the leaves of the plant. Tobacco Mosaic Virus- causes mosaic pattern on the leaves of the plant. From 1883 to 1935: Mayer, Ivanowski, Beijerinck, and Stanley first studied and ultimatley identified and named TMV in the tobacco plant. From 1883 to 1935: Mayer, Ivanowski, Beijerinck, and Stanley first studied and ultimatley identified and named TMV in the tobacco plant. Virus from the Latin for poison. Virus from the Latin for poison.

Is a virus alive? Viruses are non-cellular. Viruses are non-cellular. Viruses must have a host cell to reproduce. Viruses must have a host cell to reproduce. Viruses contain genes in DNA or RNA. Viruses contain genes in DNA or RNA. Contain a protein coat called a capsid. Viruses can invade living cells.

Viral Size & Shape nanometers nanometers –TMV~300 nm rod –Polio ~20 nm –Smallpox ~250nm –vs. Bacteria >2000 nm p53 dig 3.2 relative sizes

Genetic Material ss RNA- single stranded ss RNA- single stranded »(+)sense RNA ~~ mRNA »(-)sense RNA-transcribed 1 st ds DNA- linear or circular ds DNA- linear or circular ss DNA ss DNA

Bacteriophage A Virus that invades bacteria A Virus that invades bacteria Contains a DNA core, capsid, and tail. Contains a DNA core, capsid, and tail. Spring loaded Spring loaded

Lytic Viruses T4 virus invades host, reproduces, then lysis the host causing it to burst and spread more viruses. T4 virus invades host, reproduces, then lysis the host causing it to burst and spread more viruses. The cycle can occur as quickly as 25 minutes in T4- bacteriophage of E. coli The cycle can occur as quickly as 25 minutes in T4- bacteriophage of E. coli

Lytic Viral Cycle Infection Growth Replication Lyses adsorption

Lysogenic Virus In Lysogenic viruses(lambda phage of E.coli), the virus DNA (called prophage) is inserted into the host DNA In Lysogenic viruses(lambda phage of E.coli), the virus DNA (called prophage) is inserted into the host DNA Host DNA

Lysogenic The virus can stay in the host DNA for many generations before reproducing new virus and lyses of the host cell The virus can stay in the host DNA for many generations before reproducing new virus and lyses of the host cell Retrovirus such as HIV are lysogenic, but instead of DNA they start as RNA viruses and are covered by an envelope (lipid bilayer). Retrovirus such as HIV are lysogenic, but instead of DNA they start as RNA viruses and are covered by an envelope (lipid bilayer).

Viroids & Prions Viroids- tiny particles of pure ss circular RNA that cause disease in plants (no capsid), does not produce proteins but believed to interfere with normal mRNA processing Viroids- tiny particles of pure ss circular RNA that cause disease in plants (no capsid), does not produce proteins but believed to interfere with normal mRNA processing Origins? Origins?

Viroids & Prions Prions- protein particles that cause some diseases in animals. Prions- protein particles that cause some diseases in animals. Infections lead to neurological degenerative diseases Infections lead to neurological degenerative diseases kuru- New Guinae cannibalism kuru- New Guinae cannibalism scrapie- sheep scrapie- sheep BSE “Mad Cow Disease” in Europe BSE “Mad Cow Disease” in Europe

Teratogenic Virus Teratogens are substances that cause embryological defects Teratogens are substances that cause embryological defects TORCH series TORCH series –Blood Tests during pregnancy for –Toxoplasma protista –Other (hepatitis B & chickenpox) –Rubella (German measles) –CMV cytomegalovirus –HSV herpes simplex 1,2

Other Papillomaviruses Papillomaviruses –Warts, STD, Cancers Hepatitis B Hepatitis B –Attacks liver Influenza/Cold Influenza/Cold –RNA Herpes viruses –Oral(1) & genital/neonatal (2) herpes, –chicken pox/shingles

Treatments Interferons- substances found to be excreted by infected cells that interfere with normal viral growth. Interferons- substances found to be excreted by infected cells that interfere with normal viral growth. Purine/Pyrimidine analogue blocks Purine/Pyrimidine analogue blocks Immuno-enhancers Immuno-enhancers

Virus = Parasite A parasite is completely dependent on its host for its existence. A parasite is completely dependent on its host for its existence. Parasites do great harm to their host organisms. Parasites do great harm to their host organisms.

Review What are viruses? What are viruses? Are viruses alive? Why or Why not? Are viruses alive? Why or Why not? How can a virus be helpful to its host? What distinguished Lytic from Lysogenic viruses?