Viruses

Something you don’t want to catch…

Viruses

1. How do scientists classify things as living?

1. Made of cells2. Has a metabolism to grow and

reproduce3. Information stored in DNA

2. Are viruses alive? NO!

Living or Nonliving?

LIVING

NONLIVING

Viruses

3. What do viruses and living organisms have in common?

• Both use nucleic acids to store genetic information in the form of DNA or RNA

• Both change over time (evolve)

Viruses

4. If viruses do not have their own metabolism to grow and reproduce, how do they survive?

• By hijacking living cells and using their metabolism to grow and reproduce.

There are 2 types of viral infections• Lytic infection- a virus

enters a cell, makes copies of itself, and causes cell to burst .

• Lysogenic infection- a virus integrates its DNA into the DNA of the host cell, and the viral genetic information replicates along with the host cell’s DNA.

• Lytic Cycle• Attaches to host (1)• Injects genetic material into host(2)• Cellular machinery duplicates genetic material

and creates viral proteins (capsids, tail fibers) (3)• New viruses are assembled (4)• New viruses exit the cell by bursting the cellular

membrane (5)

• End result – more viruses made, cell dies

Viral Reproduction – Lytic Cycle

Lytic Cycle Attachment

Entry

ReplicationAssembly

Release

Viral Reproduction – Lytic Cycle

• Lysogenic Cycle• Attaches to host• Injects genetic material into host• Viral genetic material is inserted into host

genome (6)• Viral genetic material lies dormant (6)• When cell reproduces, new copies have viral

genetic information (7)• When virus is ready to exit dormant stage it will

separate from cell’s DNA and enter Lytic cycle (8)

• End result – more viral genome made, cell lives

Viral Reproduction – Lysogenic Cycle

Lysogenic Cycle

Attachment

Entry

ReproductionInsertion

Separation

Viral Reproduction – Lysogenic Cycle

Lytic Cycle•New viruses made•Cellular host dies

Lysogenic Cycle•Genome copies made•Cellular host lives

Viruses can use both cycles1.Infect many cells with lysogenic2.Create many viruses at once with lytic

Viral Reproduction

Lytic & Lysogenic Cycles

Viral Reproduction

Virus Types

• Bacteriophages = are viruses that attack bacteria

• Retroviruses = viruses that use RNA to reverse transcribe DNA that integrates into the host genome.Example: HIV

More Virus Types

• What makes these viruses different from bacteria?

THEY ARE NOT LIVING !

CHECK POINT

• This graphic shows a virus’ _____ _______.

A.Viral Reproduction

B.Viral Transription

How do you treat a virus?

• Remember you cannot treat a viral infection but you can prevent one by getting a vaccine.

Vaccine

A vaccine improvesimmunity to a particular disease.

How do vaccines work?

http://health.howstuffworks.com/adam-200097.htm

• A vaccine contains a weakened strain of the microbe.•When injected into your body it stimulates your immune system to recognize it as foreign, destroy it, and remember it.• So if your body encounters the full strain later, it can easily recognize and destroy it!!!!!

Important facts about viruses

• Viruses must be produced within living cells

• Viruses destroy the living cells they grow in

• Viruses gain entry by specific receptors on the host cell

SUMMARY

Viruses

•How do you catch many viruses?

•What are your chances of catching a virus from someone in this classroom?

Through body fluids.

• AIDS – acquired immune deficiency syndrome• Describes loss of immune system because of HIV

• Caused by HIV - human immunodeficiency virus• makes helper T cells useless

• Prevention• No vaccine• Limit transmission (use condoms)• Avoid transmission (use clean needles)

Viral Diseases - AIDS

Viral Diseases – AIDS – HIV Replication

• Initial infection• Helper T cells rapidly decline• Viral genome rapidly increases

• Clinical latency• Viral genomes lay mostly dormant in infected

cells

• AIDS• Rate of viral creation outweighs helper T cell

creation

• Death• Immune system too weak to fight common

pathogens

Viral Diseases - AIDS

• Influenza (the flu)• Causes fever, fatigue, and respiratory infections• More severe than common cold, can be deadly

Viral Diseases - Influenza

• Caused by a variety of influenza viruses– Change often, new vaccines yearly– Can blend with bird and swine

strains to produce new viruses

• Prevention– Seasonal vaccine– Limit transmission (wash hands)

Image by NIAD [Public Domain]

• The Common Cold• Causes fever, fatigue, and respiratory infections• Less severe than influenza

• Caused by a variety rhinoviruses• Over 200 different virus strains

• Prevention• No vaccine• Limit transmission

(wash hands)

Viral Diseases – Common Cold

Image by Robin S [GNU]

• Hepatitis A• Causes inflammation of liver, jaundice

appearance• Rarely results in liver failure

• Caused by a hepatitis A virus• Carried through infected food or water

• Prevention• Vaccine• Limit transmission

(wash hands, food)

Viral Diseases – Hepatitis A

Image by The CDC [Public Domain]