6/22/2016SB3D1 Viruses

Students will derive the relationship between single-celled and multi-celled organisms and the increasing complexity of systems. D. Compare and contrast viruses to living organisms. 6/22/2016SB3D2

Essential Questions  Why are viruses considered to be nonliving?  What is the lytic cycle?  What are some diseases caused by viruses? 6/22/2016SB3D3

6/22/2016SB3D4 What is a virus?  Are nonliving strands of genetic material within a protein coat.  No organelles  Cannot move  Cannot make proteins  Cannot replicate on their own  Measured in nanometers

6/22/2016SB3D5 Origin of Viruses  Viruses came from other parts of cells.  Genetic material of viruses is similar to cellular genes.

Viroids  Made of single stranded RNA  Causes disease in plants  Passed on through seeds and pollen 6/22/2016SB3D6

Prions  Prions are “infectious proteins”  They are normal body proteins that get changed into another form by contact with other prion proteins  They have no DNA or RNA  Causes disease in the brain “Mad Cow” 6/22/2016SB3D7

6/22/2016SB3D8 Scientist that studied viruses

6/22/2016SB3D9 Tobacco Mosaic Virus Wendell Stanley (1935), he crystallized sap from tobacco plants and discovered that viruses were made of nucleic acids and proteins

6/22/2016SB3D10 Smallpox Edward Jenner in 1796 developed a vaccine for smallpox using the coxpox virus.

6/22/2016SB3D11 Characteristics  Nonliving  Has a protein coat called a capsid  Made up of DNA or RNA  Can reproduce only when inside a HOST cell  Some are enclosed by an envelope  Some have spikes to attach to cells  Some infect specific cells Envelope Spikes DNA Capsid

Different shapes of viruses 6/22/2016SB3D12

How are viruses identified?  DNA or RNA virus  Do or DO NOT have a envelope  Capsid shape  HOST they infect 6/22/2016SB3D13

Bacteriophage 6/22/2016SB3D14 Will infect bacterial cells

6/22/2016SB3D15 Lytic Cycle  1. Attachment to the cell  2. Penetration (injection) of viral DNA or RNA  3. Replication (Biosynthesis) of new viral proteins and nucleic acids  4. Assembly (Maturation) of the new viruses  5. Release of the new viruses into the environment (cell lyses)

6/22/2016SB3D16 The virus may enter the lysogenic cycle, in which the host cell is not destroyed.

6/22/2016SB3D17 Lysogenic Cycle  Viral DNA injected into host cell  Viral DNA joins host DNA forming a prophage  When an activation signal occurs, the viral DNA starts replicating  Viral DNA (part of prophage) may stay inactive in host cell for long periods of time  Replicated during each binary fission  Over time, many cells form containing the prophages

6/22/2016SB3D18 The viral DNA is called a prophage when it combines with the host cell’s DNA. Although the prophage is not active, it replicates along with the host cell’s DNA. Many cell divisions produce a colony of bacteria infected with prophage. The prophage may leave the host’s DNA and enter the lytic cycle. i

6/22/2016SB3D19

Infectious Diseases due to viruses  Common cold  Influenza  SARS Respiratory disease similar to the flu. Respiratory disease similar to the flu. Fever, coughing, difficulty breathing Fever, coughing, difficulty breathing  HIV Retrovirus Retrovirus Destroys white blood cells which causes AIDS Destroys white blood cells which causes AIDS 6/22/2016SB3D20

Retrovirus Viruses that have RNA instead of DNA for their genetic material Viruses that have RNA instead of DNA for their genetic material Use reverse transcriptase to make DNA from RNA Use reverse transcriptase to make DNA from RNA Retroviruses have a protein capsid Retroviruses have a protein capsid Lipid envelope is obtained from the plasma membrane of a host cell Lipid envelope is obtained from the plasma membrane of a host cell Ex: HIV Ex: HIV 6/22/2016 SB3D21

Vaccines  Made from weak weakened pathogens  Stimulates the body’s own immune response 6/22/2016SB3D22