VIRUSES Latin for “poison”

VIRUS: a particle that can only be seen with an electron microscope It is different from a cell because it does not: contain a nucleus or cytoplasm have any metabolic activity

A virus is surrounded by a capsid (protein coat) which determines the shape of the virus. Core of nucleic acid ( DNA or RNA) Tail fibers for attachment to host cell.

Some viruses have an envelope. An additional protective covering made up of lipids, proteins and carbohydrates. Found only in animal cells. envelope

INFLUENZA VIRUS Core of RNA Envelope Protein Coat Projections

Pathogen - a virus that causes disease Virulent - a virus that causes illness & death. EbolaInfluenza

VIRAL DIVERSITY Classifying viruses is difficult because they are so diverse. Biologists identify viruses by various ways such as: (1). shape (2). type of host cell (3). DNA or RNA

VIRAL SHAPES Binal Virus Helical Virus Polyhedral Virus Filovirus

VIRAL REPLICATION - Viruses do not reproduce, they replicate (make a copy of self) - Require a host cell - A host cell is a living organism that shelters and nourishes the virus. - Two cycles: Lytic or Lysogenic

Lytic Cycle The viral replication process that begins immediately and rapidly kills the host cell.

LYTIC CYCLE Virus attaches to host cell and injects its DNA Viral DNA forms a circle Viral DNA commands host cell to make new viruses Coats & tails assemble Cell lyses (breaks apart) and new viruses are released

LYSOGENIC CYCLE -Does not begin immediately -Viral DNA (called a prophage) attaches to a host cell’s chromosomes – lies dormant. -Environmental stimulus sends viral DNA into lytic cycle.

LYSOGENIC CYCLE

What is a Prophage? (Provirus) A viral DNA segment that has become part of a host cell’s chromosome.

VIRAL DISEASES DiseaseTransmissionSymptoms AIDS/HIV Sexual contact; contaminated blood or needles Immune system failure; fatal CommonCold Inhalation, direct contact Sinus congestion, muscle aches, cough, fever SmallpoxInhalation Blisters, lesions, fever, blindness, scars; often fatal Influenza(Flu)Inhalation Headache, muscle ache, sore throat, cough, fatigue, fever, chills Warts Direct contact Lumps on skin or mucus membranes

SMALLPOX

MEASLES

HERPES

What is a Retrovirus? A retrovirus contains an RNA core that replicates first by transcribing its RNA into DNA. Requires an enzyme called reverse transcriptase (Ex: HIV). “Retro” means “reverse.”

HIV & Influenza are examples of a retrovirus. AIDS (Acquired ImmunoDeficiency Syndrome) is caused by the infection of HIV (Human Immunodeficiency Virus.

is contracted through semen, blood & vaginal fluid. THERE IS NO CURE - ONLY WAY TO PREVENT IS ABSTINENCE!

Most viruses have NO cure (Influenza, & HIV), but some viruses like Smallpox have vaccines. Vaccines contain a weakened or killed virus that provides immunity to the disease.

PUTTING VIRUSES TO GOOD USE Viruses have many good uses: Vaccines Genetic Engineering Agriculture