what … have genetic material and can mutate and evolve, can not metabolize food, can not respond...
TRANSCRIPT
What …
• have genetic material and can mutate and evolve, • can not metabolize food, • can not respond to stimuli,• are not made up of cells, • can only reproduce inside of a host cell, • act as nonliving chemicals when outside a host cell,• form parasitic relationships with living organisms?
Pseudo-Life Forms…Viruses
Structure…
Viruses contain an inner nucleic acid core (genetic material) and an outer protein coat (capsid).
25 nm
Lipid envelope
Protein Receptors
Nucleic Acid (RNA)Capsid: core protein coat
Enzymes
Diagram of a Retrovirus or RNA carrying virus
Enveloped Virus
Protein Receptorson tail fibers
Capsid: core protein coat
Nucleic Acid (DNA)
Diagram of a Bacteriophage or T4 DNA carrying virus
Naked Virus
Viruses …Structure
• The virus may also contain some enzymes.
• An outer envelope (membrane) that is derived from the cell membrane of the host cell may surround the capsid.
• The envelope contains viral protein spikes.
• They are usually smaller than 200 nm.
What is a Nanometer?
Virus (20-50 nm)Tobacco Smoke (100 -1,000 nm)Bacteria ( 3,000-5,000 nm)Fungus Spores (5,000- 30,000 nm)Plant Pollen (10,000- 80,000 nm)Rain Droplet ( 600,000 – 10,000,000 nm)
Object Characteristic Sizeperson 1 m = 1000 mmgrain of sand 1 mmhuman hair (thickness) .1 mm = 100 µmred blood cell 10 µm wavelength of light 1 µm = 1000 nm virus 100 nmatom .1 nm
What is a Nanometer?
1 m 103 mm 106 µm 109nm ~ Viron size ranges from 20-200 nm
Viruses… Structure
•The genetic material in some viruses is DNA; in others it is RNA (as in retroviruses).
•Both nucleic acids (NA) strands can be either a double (ds) or single (ss) stranded.
Viruses…Reproduction
…requires viruses to be in intimate contact with a specific host organisms and a specific type of cell within that host.
This is called virus-host Specificity
Examples:Influenza infects cellslining the respiratory tracts.
Poliomyelitis virus infects nerve cells.
Tobacco mosaic virus infects tobacco leaves.
Viruses…Reproduction
Life Cycle…Lytic
1 - Adsorption
2 – Entry
3 – Replication
4 – Viron Assembly
5 – Lysis / Exit
Viruses…Cycles
…requires the virus to enter a cell when either a part of the capsid or the spikes in the envelope match receptors in the host cell.
Viruses…Cycles
Adsorption
Reinfection
Some viruses, capable of causing cell fusion, may be transported from one cell to adjacent cells without being released, that is, they are transmitted by cell-to-cell contact whereby an infected cell fuses with an uninfected cell.
Viruses…Cycles
Reinfection
As many as 10,000 to 50,000 animal viruses may be produced by a single infected host cell.
Viruses…Cycles
How does a Vaccination Work?
1 – Injection of broken virus particles
2 – Body responds by making particles that recognize the virus and kiling to it - antibodies
3 – White blood cells collect and digest foreign particles covered in antibodies.
Read pages 1063-1076
Viruses…Interrupting The Cycle