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Viruses & Microorganisms By Dr. Rick Woodward

Today’s Agenda:

a. Journal Question: Identify three diseases transmitted in your saliva.

*1. Lecture III: Viruses & Microorganisms

2. Video: The Spreading Menace

3. Homework: Read Chapter 25 (pp.486 – 500)

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Did you know?Spotlight: Gym Equipment The threat: A 2006 study in the Clinical Journal of

Sports Medicine found rhinoviruses (instigators of the common cold) on 63 percent of the gym equipment at the fitness centers they tested.

Researchers also discovered that weight equipment was contaminated significantly more often than aerobic equipment (73 percent versus 51 percent). Even worse, the study found that disinfecting the equipment twice a day didn't do anything to lower the virus count.

The Solution: Avoid touching your face between sets, since most colds are transmitted through hand-to-nose contact. And make sure to pack an alcohol-based hand sanitizer in your gym bag.

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Did you know? Spotlight: Restaurant Menu

The threat: Ever see anybody wash a menu?

- A recent study in the Journal of Medical Virology reports that cold and flu viruses can survive for 18 hours on hard surfaces. If it's a popular joint, hundreds of people could be passing their germs on to you.

- The Solution: Never let the menu touch your plate or silverware as you ponder the wine list, and wash your hands after you order. But how do you escape the bathroom without touching the door handle? Palm a spare paper towel after you wash up, and then use it to grab the handle. Execute this trick properly and nobody needs to know how much you fear germs.

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Did you know? Spotlight: Flight Attendants

The threat: Flight attendants are exposed to dozens of sniffling and coughing passengers and the surfaces they touch.

When attendants need a restroom break, they head into the same latrine you use.

Now consider that when Charles Gerba, Ph.D., coauthor of The Germ Freak's Guide to Outwitting Colds and Flu, tested commercial-jet bathrooms, he found that surfaces from faucets to doorknobs were contaminated with E. coli. Given all that germ exposure, it's no surprise that the Journal of Environmental Health Research recently revealed that you're 100 times more likely to catch a cold while flying than on the ground.

The Solution: Pack a green-tea pill. In a 2007 University of Florida study, people who took a 450-milligram green-tea supplement twice a day for 3 months had a third fewer days of cold symptoms. Try Immune Guard ($30 for 60 pills, immune-guard.), the brand used in the study.

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Did you know? Spotlight: Lemon Wedge in your Water

-The threat: In a 2007 study from the Journal of Environmental Health, nearly 70 percent of the lemon wedges smashed into restaurant glasses contained disease-causing microbes.

-Researchers ordered drinks at 21

different restaurants, securing 76 lemons. Testing revealed 25 different microorganisms lingering on the lemons, including E. coli and other fecal bacteria.

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What is a virus?1. Viruses are not organisms.

2. Viruses have no cytoplasm and no organelles.

3. Virus is the Latin word for poison.

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What is a virus?4. Viruses are quite small. (Smaller

than bacteria)

a. They cannot be visualized with the light microscope.

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Size Comparison: Bacteria versus Virus

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What is a virus?5. Viruses are particles capable of

reproduction at the expense of specific host cells

a. A virus needs chemicals and ribosomes of the healthy cells it invades in order to reproduce.

b. Virus particles are called “virons.”

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What is a virus?Recall: Prions are the

causative agent in “Mad Cow” disease.

6. Viruses are capable of invading only specific cells.

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Prions in Mad Cow Disease

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What is a virus?7. Viruses have a nucleic

acid component.

a. Either DNA or RNA

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Virus Structure1. Viruses are composed of:

-An outer protein coat that encloses a nucleic acid.

a. A capsid or protein coat.

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Virus Structureb. Nucleic Acid (DNA or RNA)

c. In some instances, an outer membranous envelope.

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Virus Structure

d. The viral genome can be coated with proteins forming different viral shapes:

(1) Spherical (AIDS virus)

(2) Polyhedral head with tail fibers (Bacteriophage)

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Virus Structure(3) Polyhedral (Polio virus)

(4) Rod-Shaped (Tobacco mosaic virus)

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Viral Cycles

1. When a virus invades a cell, new viruses are produced.

2. The invaded cell is called a host because it provides materials to the virus.

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The Lytic Cycle (Search & Destroy Mission)

1. A virus can identify and infect a potential host cell only if part of the viral coat can match a specific receptor site on the membrane surface of the host cell.

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Lytic Cycle(1) e.g. HIV can only attack

certain white blood cells called T-Lymphocytes in the immune system.

(Recall: The immune system protects you from getting sick by destroying pathogens, which are disease causing agents)

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Lytic Cycle(1) a. T-Lymphocytes have a

specific protein receptor site called CD4.

b. CD4 is believed to be the site where HIV’s viral protein GP120 attaches.

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HIV Viron

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Lytic Cycle(2) e.g. The tobacco

mosaic virus can only invade and attack the leaf of the tobacco plant.

-Viruses are very specific when it comes to finding a host.

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Search & Destroy Mission of an Active Virus (Using a DNA Virus)

First the virus has to find a viable host

(Virus recognizes appropriate receptor site)

1. Attachment to host

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Search & Destroy Mission of an Active Virus (Using a DNA Virus)

2. Entry (Inject nucleic acid into host cell).

3. Viral DNA takes over and replication begins.

a. Host DNA is destroyed and the new viral nucleic acids and proteins are made.

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Search & Destroy Mission of an Active Virus (Using a DNA Virus)

4. Formation of new virus particles.

(Virons are assembled)

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Search & Destroy Mission of an Active Virus (Using a DNA Virus)

5. Host cell breaks open (lysis); New virus particles are released.

Lysis & Release

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Search & Destroy Mission of an Active Virus (Using a DNA Virus)

A. Facts about an “Active Virus.”

(1) This entire process (Steps 1-5) is called the

lytic cycle

(2) Lysis can occur as quickly as

20 minutes after attachment!!!

(3) During the lytic cycle, a virus takes over the metabolic activities of its host cell, makes many copies of itself, and destroys the cell.

(4) Antibiotics ( e.g. Penicillin) do not kill viruses.

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Some Examples of Active Viruses:

1. Influenza (Flu) Virus

a. Avian (Bird) Flu Virus

2. HIV

3. Hanta Virus

4. Ebola Virus

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Influenza (Flu) Virus

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Avian (Bird) Flu Virus

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HIV Virus

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Hanta Virus

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Ebola Virus

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West Nile Virus

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Birds that carry the West Nile Virus

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Lysogenic Viruses Provirus

1. After attachment and entry, viral DNA may sometimes become integrated into the host cell’s chromosome.

a. When this occurs, the viral DNA is known as a provirus.

b. A provirus can also be called a latent virus.

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Lysogenic Viruses2. When a cell that contains a provirus is

exposed to environmental factors like:

(1) X-rays

(2) Chemicals

(3) UV light from the sun (sunburn)

(4) Stress

(5) Extreme changes in temperature

*Any of these factors can trigger a provirus to become active.

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Lysogenic Viruses3. Provirus triggered to become

active:(1) The viral DNA take over the machinery.(2) New viruses are manufactured.(3) The host cell lysis occurs.(4) The new viruses are released to invade other cells.-The pattern of reproduction is called the lysogenic cycle.

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Some Examples of Lysogenic Viruses:

1. Herpes: The gift that keeps giving.

(The gift you don’t want!)

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Summary of Viral Cycles

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RNA VirusesA. Most viruses containing

RNA go through the same lytic and lysogenic cycles as DNA viruses.

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RNA Viruses1. RNA viruses that enter the

lysogenic cycle are unusual.

2. They contain RNA, but their host cell’s genetic material is DNA.

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RNA Viruses

3. How can viral RNA attach to the host’s DNA to become a provirus?

-Answer: These viruses contain a unique enzyme called reverse transcriptase, which reverses the normal transcription process.

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Using Reverse Transcriptase

1. Instead of transcribing DNA to RNA, reverse transcriptase transcribes RNA to DNA.

2. Once the DNA has been transcribed, it can be double stranded by replication and join the host’s chromosome.

3. Because the viruses perform transcription backwards, these viruses are called retroviruses. (retro means backward)

4. The virus that causes AIDS is an example of a retrovirus.

Next Topic: Bacteria

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