VIRUSES Chapter 24 Video VIRAL STRUCTURE AND REPLICATION

VIRUSES Chapter 24 Video

VIRAL STRUCTURE AND REPLICATION Section 24. 1

Discovering Viruses: n Late 1800’s – Something very small is causing diseases! n 1935 – It is not made of cells (living things). TMV Polio HIV

What is a virus? n. A nonliving particle composed of a nucleic acid and a protein coat. n Study of viruses = virology

Why do we study them? n Cause disease in living organisms n Useful tools for genetic research

Are viruses living? The Characteristic of life: growth homeostasis metabolism organization cells reproduction n Viral characteristics: NO NO NO YES NO within host cell

Common Diseases Caused by Viruses n AIDS n Influenza n Chickenpox n Rabies n Polio n Mumps n Colds

Viral Structure n n All viruses have: 1. Nucleic acid: (DNA or RNA) 2. Capsid: protein coat Some viruses have: 1. Glycoprotein projections: signals 2. Envelope: Bilipid membrane surrounding the capsid. § Can fit “lock-and-key” with receptors on host cell.

HIV

Grouping viruses based upon… SHAPE AND STRUCTURE: n Envelope present or not? n DNA or RNA? n Single stranded or double stranded? n How does it affect a human? Rabies Hepatitus Herpes

Viral Size & Shape n Size: – 20 to 250 nm – Cannot be seen by a light microscope n Shape: – Determined by the genome (DNA) or capsid

Some shapes: H 1 N 1 or influenza Video

Viral Replication: Obligate Intracellular Parasites (huh? )

Viral Replication in Eukaryotes n DNA viruses: – DNA m. RNA proteins – Provirus: inserted viral DNA into host cell n RNA viruses: – m. RNA protein n Retroviruses: – RNA DNA m. RNA protein – Reverse transcriptase: enzyme – Example: HIV

Viral Replication in Prokaryotes n Bacteriophage: virus that infects bacteria n Helped scientists discover how viruses replicated n Two replication cycles – Lytic cycle: virulent – Lysogenic cycle: temperate

L Y T I C C Y C L E Animation

L Y S O G E N I C C Y C L E Animation

Origin of Viruses n Early viruses evolved from early cells n Viruses mutate quickly and frequently – Thus they evolve quickly – New strains formed this way

Viral Disease Section 24. 2 Flu Video

Vectors n An intermediate host that transfers pathogens from one organism to another n Examples: – – – Humans Animals mosquitoes Fleas ticks

Chicken Pox & Shingles n Virus: varicella-zoster herpesvirus n Symptoms: rash & fever n Replication: Multiplies in lungs and uses blood network to reach skin n Transmission: direct contact with skin rash

Viral Hepatitis n Virus: Hepatitis A, B, C, D, E n Symptoms: – Fever, nausea, jaundice, liver failure n Transmission: – Sexual contact (B, C, D) – Fecal matter in food & water (A, E)

AIDS n Virus: HIV – retrovirus Transmission: through bodily tissues and fluids n Symptoms: weakened immune system n n Treatment: Drugs target reverse transcriptase OR stop new capsids from forming (protease inhibitors).

Viruses and Cancer n Cancer: when cells divide at an uncontrolled rate and form a tumor n Oncogenes: viral genes that cause cancer n Examples: – HPV cervical cancer – Hepatitis B liver cancer – Epstein-barr lymphoma

Emerging Viruses n New viruses are being discovered every year as humans alter ecosystems n Examples: – – HIV Ebola SARS West Nile

Preventions and Treatments 1. Vaccinations: to prevent disease q Solution containing harmless version of virus q Causes an immune response in the body 2. Vector Control: n Wildlife population control 3. Drug Therapy: n Interfere with viral nucleic acid

2 types of Vaccines: Inactivated (killed)- virus particles 2. Attenuated (live)- weakened form of the virus 1. – Provide greater protection from disease • Has lead to the eradication of some diseases ex) smallpox • Common vaccines: measles, mumps, rubella, polio, hepatitis A & B, chickenpox

How to protect yourself and others… 1. Wash your hands! 2. Don’t share tools (cups, toothbrushes) 3. Use protection when transmitting bodily fluids 4. Don’t become someone’s “Blood brother” 5. Avoid being bitten by animal 6. Cover your mouth when sneezing

Non-virus Disease Causers: Viroids – a short singular strand of RNA § smallest known particle to cause disease § infects mostly plants Prions - protein particles without a genome § mad cow disease

Practice Graphing Problem