The Amazing World of Viruses

2 Viral History

3 Discovery of Viruses Beijerinck (1897) coined the Latin name “virus” meaning poison He studied filtered plant juices & found they caused healthy plants to become sick

4 Tobacco Mosaic Virus Wendell Stanley (1935) crystallized sap from sick tobacco plants He discovered viruses were made of nucleic acid and protein

5Smallpox Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses Deadly viruses are said to be virulent Smallpox has been eradicated in the world today

6 Viewing Viruses Viruses are smaller than the smallest cellViruses are smaller than the smallest cell Measured in nanometersMeasured in nanometers Viruses couldn’t be seen until the electron microscope was invented in the 20 th centuryViruses couldn’t be seen until the electron microscope was invented in the 20 th century

Interdependence Viruses and organisms rely on their environment and other species for survival.

Viruses But, Viruses are NOT cells. A virus is an infectious agent made up of: a core of nucleic acid (RNA or DNA) a protein coat

Alive or not? Even scientists disagree as to whether or not viruses are alive. What do you think? Look at the chart on the next page to help you decide.

CELLVIRUS Made of cellsYESNO Obtain & use energy YESNO Grow & developYES Only inside a living cell ReproduceYES Only inside a living cell Respond & adapt YES Contain RNA or DNA YES Characteristic of life

Alive or not? Most scientists do not consider viruses to be living because don’t have the necessary parts to reproduce on their own. They MUST infect a cell and use its parts to reproduce.

Structure of a virus Because viruses don’t carry around the necessary parts to reproduce themselves they are very simple structures. ENVELOPE NUCLEIC ACID CAPSID

Structure of a virus Consists of 2 parts: 1.A Nucleic acid - either DNA or RNA 2.Capsid – A protein Coat that surrounds and protects the DNA/RNA ENVELOPE NUCLEIC ACID CAPSID

Types of Viruses 1.Standard DNA based Virus 2.Retro Virus 3.Bacteriophage

Basic Virus A strand of nucleic acid surrounded by a protein coat. DNA  RNA  Protein

Retrovirus A virus that contains RNA instead of DNA Human Immunodeficiency Virus (HIV) is a retrovirus HIV causes AIDS ENVELOPE RNA CAPSID

Bacteriophage A virus that infects only bacteria. CAPSID DNA TAIL FIBER HEAD CAPSID

21 Helical Viruses

22 Polyhedral Viruses

23 Complex Viruses

24

Ticking time bombs... Viruses CANNOT reproduce, EXCEPT inside a living cell. They invade a living cell and let the cell work for them.

Virus Cycle A Viral Infection has 2 possible stages: 1.Lytic Cycle 2.Lysogenic Cycle *Some viruses go straight to the lytic phase and never enter the lysogenic phase

Virus Cycle 1.Lytic Cycle - stage where virus is actively reproducing and killing host cells 2.Lysogenic Cycle - stage where virus is inactive and host cells remain unharmed

Lytic Cycle 1.The virus injects its DNA into the host cell 2.The DNA uses the host cell’s resources and organelles to make new viruses. 3.The viruses cause the cell to burst 4.The cell dies and the newly made copies of the virus are released to go infect new cells. 5.The cycle continues.

Cycle Illustration

Lysogenic Cycle 1.The Virus injects its DNA into the host cell. 2.The DNA inserts itself into the host cell’s DNA and stays there inactive. 3.There are NO symptoms of the infection at this stage. 4.Eventually the viral DNA will remove itself from the host cell’s DNA and the lytic cycle will begin.

Lytic Cycle Lyso- Genic Cycle

Role of viruses All viruses are parasites: they benefit while harming the host cell/organism. Viruses cause disease in every kind of organism—animals, plants, fungi, protists, and bacteria.

Are hard to cure, but many can be prevented by Good hygiene Immunization Viral diseases

HIV Measles Smallpox Influenza Chicken pox Common cold Herpes Warts Mononucleosis Mumps Some viral diseases

MEASLES

Mumps

SMALLPOX

HERPES

1918 Flu

41 Herpes Virus SIMPLEX I and II

42 Adenovirus COMMON COLD

43 Influenza Virus

44 Chickenpox Virus

45 Papillomavirus – Warts!

46 Helical Viruses

47 Polyhedral Viruses

48 Complex Viruses

Links

Biology, Kenneth R. Miller & Joseph Levine, 1991, Prentice-Hall, Inc., Englewood Cliffs NJ. Biology: The Web of Life, Eric Strauss & Marylin Lisowski, 1998, Scott Foresman Addison Wesley, Menlo Park CA TAKS Power Tools, Glencoe Science, Glencoe McGraw-Hill, 2001, New York, NY. Microsoft Office Clipart Sources