VIRUSESSB3.d. Compare and contrast viruses with living

organisms.EQ: Why are viruses considered to be non-living?

Characteristics:

*Nonliving particles made of nucleic acid and a protein coat enlosed in a capsid shell..*In order to reproduce, all viruses must have a HOST.

capsid

Nucleic acid

Proteins

Envelope

The_Littlest_Assassins__What_Are_Viruses_.asf

Alive or Not???

Characteristics that make them seem alive:1. They have DNA.2. They can evolve.3. They can adapt to their environment.4. They can reproduce5. They can cause disease!

Reasons why they are NOT living things:

1. They are not made of cells.2. They do not use energy, grow, or reproduce.3. They can only reproduce when inside a host.4. They can form crystals and remain for long periods of time.

*Viruses are MUCH smaller than bacteria. *They can only be seen with an electron microscope.

Viral Structure:

-The nucleic acid in a virus can either be DNA or RNA.-The protein shell that surrounds a virus is

the capsid.

-The viral envelope is a protective coating around a virus.

-Viruses use their spikes to recognize and attach to the cells they infect.

capsid

viral envelope

Did you know???

* Viruses are not the only particles that can cause disease.

* A protein known as a prion, and a piece of RNA known as a viroid, can also cause disease.

Potato disease

KuruIn the 1950s-1960s, kuru reached epidemic proportions in the South Fore tribe of Papua New Guinea. Although researchers do not know how it started, they know it spread when tribal members ritualistically consumed the tissue of affected people during funeral rites. Kuru is characterized by walking problems, shaking of the limbs, slurred speech and mood changes, but little or no dementia. It is usually fatal within 6 to 12 months. Kuru disappeared with the end of cannibalistic practices in New Guinea.

How are viruses named?

-They are often named for the type of organism they infect or the diseases they cause.

bact

erio

phag

e

HIV

tobacco mosaic

Mad Cow

disease

What is a bacteriophage?

A virus that infects bacteria.

https://www.youtube.com/watch?v=rzdwfwuVWUU

Viral Replication:The process by which viruses reproduce.

First, the virus attaches itself to a host cell. If then injects its DNA or RNA into the cell. Once inside the host cell, the viral DNA is added to the host's DNA. The viral DNA is then copied along with the host cell each time the cell prepares to divide. When the cell divides, the viral DNA is passed on to each new daughter cell. In many cases, once viral DNA is inserted into a cell, the virus may remain inactive, and have no apparent effect on the cell.

*If a virus is benign, it causes little or no harm to the host cell.

Lytic cycle animation

*Sometimes the virus does not immediately kill the host cell but undergoes a lysogenic cycle where it embeds its nucleic acid into host DNA . It may remain dormant for years and suddenly become active and undergo the lytic cycle.

Ex: Chicken pox virus can lie in body many years and later cause shingles.

Fever blisters (cold sore) viruses may become active after stress, cold, etc...

*Viral diseases cannot be treated with antibiotics because they are not cells.

*Many viral diseases can be prevented by vaccines which may give life-long immunity to the virus. Some require booster shots.

Vaccines_and_the_Treatment_of_Viruses.asf

Why are viruses difficult to cure?

*They can replicate very quickly!

* They undergo frequent mutations that change their characteristics.

*Medicines used to destroy viruses often attach and harm healthy cells.

Diseases caused by viruses:

Mumps, measles, chicken pox, hepatitis, polio, small pox, colds, flu, fever blisters, and AIDS in humans. Also causes rabies as well as diseases in plants and other organisms.

Closing Activity:

Take (5) of the following words and write a paragraph summarizing what you did today.

-virus-nucleic acid-disease-host-reproduce-antibiotics-vaccines-lytic cycle-lysogenic cycle-dormant

Attachments

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Vaccines_and_the_Treatment_of_Viruses.asf