Lesson 3Viruses

Virus

• Tiny “organism” that is parasitic to cells• Composed of two main parts:• Protein outer shell called capsid• Genetic material inside (DNA or RNA)

• Not classified as living• Do not have cells• Require cells to replicate

• Likely evolved after cells came into existence

Virus

• Cause some of the most common illnesses, ex:• Common cold, the flu, cold sores, etc

• Cause some of the deadliest diseases, ex:• Ebola, avian flu, AIDS

Virus

• Cannot be killed by antibiotics• Antibiotics kill bacteria

• People can be protected against viruses with vaccines• Ex. Flu shot

RNA or DNA?

• Viruses with RNA (higher mutation rate)• Human immunodeficiency virus (HIV)• Influenza viruses• Rabies• Measles, mumps, pneunomia, polio, common cold• SARS

• Viruses with DNA (usually stable/constant, vaccines effective )• Chickenpox, cold sores, genital herpes• Mononucleosis• Hepatitis• Respiratory infections, tumours

Virus Shapes

1. Helical (a spiral rod)

2. Polyhedral (many sides)

3. Complex (polyhedral capsid attached to a helical tail)

Virus reproduction

• Go through process called “Lytic Cycle”

Virus reproduction

• Go through process called “Lytic Cycle”

Virus reproduction

• Go through process called “Lytic Cycle”

Virus reproduction

• Go through process called “Lytic Cycle”

Virus reproduction

• Go through process called “Lytic Cycle”

Viruses are host cell specific• Viruses usually infect only 1 type of host or even

one cell type• Some viruses can infect many species• Ex. Rabies, swine flu

How are viruses spread?

• Vectors – carriers of viruses from one host to another• May include:• Insects (yellow fever, West Nile)• Animals (rabies)• Water (polio)• Air (influenza, common cold, chicken pox)• Humans (influenza, hepatitis, HIV)

Virus applications

• Studying molecular biology• Genetically modify organisms• Virotherapy: using viruses to treat diseases• Kill bacteria• Kill cancer

• Insecticide• Biological warfare

Homework

1. What is a virus?2. Are viruses alive? Why or why not?3. Name 2 characteristics of viruses4. What is the difference between a host and a

parasite?5. What are 3 different vectors for viruses?6. Can a tobacco mosaic virus infect a human? Why

or why not?7. Describe the life cycle of a virus.