Section 20-2

1. Section 20-2 Viruses

2. Living or Non-living? • Viruses are considered nonliving because:

3. Recall the Cell Theory—one of the components of the Theory is that all living things are comprised of cells. • Looking at the chart, viruses are not cellular • They aren’t even given a place in the Linnaean classification system!

4. Virus • A virus is an infectious particle made only of a strand of DNA or RNA surrounded by a protein coat (capsid)

5. Two essential features of all viruses: • 1. Nucleic acid present: DNA or RNA • 2. Protein coat called a capsid • Sometimes there may be an extra membrane outside the capsid called an envelope which helps the virus enter cells • Consists of proteins, lipids, glycoproteins (proteins with attached carbohydrate molecules) used for host cell recognition

7. Some common viral shapes include helical (tobacco mosiac virus) or polyhedral (adenovirus) on page 476

8. Bacteriophages (viruses that infect bacteria) have complicated structures • Tail fibers may function like a syringe to inject the viral DNA into its host • Since viruses rely on host cells to carry out replication, they can enter all types of cells in various ways

9. Once inside, viruses will take on one of two viral cell cycles: Page 478 • Lytic Infection (or Cycle) • Virus attaches to the host cell • Viral DNA is injected into host cell • Viral DNA is replicated • Virus is assembled using energy from host cell • Host cell lyses and releases new viruses

10. Lysogenic Infection (or Cycle) • Virus attaches to the host cell • Viral DNA is injected into host cell • Viral DNA integrates with host DNA making a provirus • When the host cell divides, the provirus divides making more infected host cells • In some cases, a stimuli can cause the provirus to begin the lytic cycle • Ex. Herpes Simplex I aka cold sores • OR the provirus can remain dormant as a permanent gene

12. Viroids • Viroids are infectious disease agents that have a single strand of DNA but no capsid • They replicate inside a host’s cell to make new viroids and disrupt a host cell’s growth regulation

13. Prions • Prions are misshapen versions of proteins found in the brain • Affect how proteins fold • The misfolding of proteins can spread and destroy brain tissue • Ex. Mad Cow disease, spread by eating food contaminated with infected brain tissue

14. Section 20-3: Bacteria, Viruses, and Humans • Bacteria • Produce oxygen—what kind of bacteria would do this? • Fix nitrogen for other organisms—what kind? • Decompose dead organisms—what kind? • Produce Vitamin K in human intestines—what kind?

15. Used to make foods like pickles, soy sauce, sourdough bread, cheese, yogurt, etc…

16. Used to make chemicals like acetone • Used in mining copper and uranium • Used to clean up oil spills and sewage treatment plants

17. Some viruses and bacteria are pathogens meaning they cause disease • Robert Koch developed a technique for diagnosing the cause of an infection • Pathogen must be present in infected animal and not healthy animals • Isolating the pathogen from an infected animal • Isolated pathogen must be injected into a healthy animal in order to develop the disease • The pathogen should be extracted from the second animal and grown in the lab

19. Name a few different ways contagious diseases can be transmitted… • Direct contact • Through the air • In contaminated water or food • Sexual intercourse • Exchange of bodily fluids

21. Bacteria can cause disease by producing poisonous chemicals, toxins, and by producing enzymes that destroy body tissues. • What is the name of the endospore-producing bacteria used in Botox, a de-wrinkling cosmetic procedure? • Clostridium botulinum

22. Antibiotics are chemicals that inhibit the growth of or kill microorganisms • Overusing these chemicals can lead to antibiotic resistance which is the ability of bacteria to tolerate antibiotics, this is a great example of rapid evolution • What are some consequences of antibiotic resistance?

23. Because viruses enter host cells to reproduce, it is difficult to develop a drug that kills the virus without harming the living host • A vaccine is a weakened form of a pathogen that prepares the immune system to recognize and destroy the pathogen

24. Influenza or “Flu” • Usually causes an epidemic—a rapid outbreak of an infection that affects many people • Up to 20% of US population is infected per year • Some can be transferred across different species • New vaccines must be developed to overcome the rapid mutation of the capsid proteins • A vaccine is a weakened form of a pathogen that prepares the immune system to recognize and destroy the pathogen

25. Some viruses are pathogens meaning they cause disease • List of pathogenic viruses on page 554 • Some viruses also cause cells to grow uncontrollably causing cancers • Ex. Hepatitis B -> liver cancer, HPV (Human Papilloma Virus) -> cervical cancer HPV Facts

26. HIV—Human Immunodeficiency Virus • Is a retrovirus—a virus that contains RNA and uses reverse transcriptase (an enzyme) to make a DNA copy • Enzyme used to make a double-stranded DNA from the viral RNA • The DNA is then used to make a provirus and proceed in lysogenic cycle • The lysogenic cycle can last between 8-10 years or even longer

28. Infects white blood cells, which are important for your body’s normal defense • Over time, HIV will develop into AIDS once more cells go into lytic cycle and infect the white blood cells • When enough white blood cells are destroyed, the body will no longer have the defense it needs to fight off sickness and will succumb to AIDS (Acquired Immunodeficiency Syndrome) • HIV is transmitted through bodily fluids by sexual intercourse, sharing needles, pregnancy, or breast milk

29. Emerging Viruses • Are becoming more prevalent in today’s society • These are viruses that evolve in geographically isolated areas and are pathogenic to humans • Ex. Hantavirus was first detected in the Southwest of US • Started in rodent vectors and is lethal to humans • 40-50% of victims dies • Hantavirus symptoms • Ebola in Africa • Symptoms