Viruses

Do you think a virus is a living cell?Use the picture and this information to

help you make your decision:

1. Viruses contain RNA or DNA

2. Viruses cannot replicate on their own, they must use a host cell to replicate and survive

3. Viruses do not contain ribosomes or any other type of organelle

Are viruses alive? NO!Viruses cannot perform cellular processes or replicate without a host organism so scientists have classified them as non-living organisms.

What types of organisms can viruses infect?

Anything that is made of cells!PlantsAnimalsBacteria

But – viruses are very species specific!HIV - human white blood cells SIV - chimpanzees white blood cells bacteriophage - bacteria cells

Virus Structure Virus Structure: All viruses contain:

1. Protein Coat (Capsid)-protects genetics information-recognizes host cell

2. Nucleic Acid (DNA or RNA)-contains genetic information

Influenza Virus

HIV Virus H1N1 Virus

Herpes Virus

AIDS VIRUS(HIV)

Viral Replication:The Lytic Cycle of bacteriophage

1. Virus attaches to host cell and inserts it’s DNA

2. Virus directs host cell to synthesize proteins and nucleic acids (DNA/RNA)

3. Newly created virus components (DNA/RNA, protein coat) are assembled to form new virus particles

4. Cell lysis: Host Cell explodes releasing newly synthesized viral particles

***** The lytic cycle results in death of the host cell!******

Sneaky Viruses

Some viruses are lysogenicThey insert their genetic material into the host

cell’s DNA for long periods of time. Years, even!

Every time the host cell copies its DNA it makes a copy of the virus DNA as well.

The virus may switch to the lytic cycle at any time.

Examples include: herpes (cold sores), shingles, warts, HIV/AIDS

Can viruses be helpful? Viruses are sometimes used to attack bacteria

that cause disease. For example, bacteriophages destroy bacteria, but not human cells

Viruses insert “good genes” into people with genetic diseases. This is called gene therapy.

Viruses are used to create genetically modified foods. They introduce desired traits (genes) into plants and animals.