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

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

10 x smaller

100 x smaller

1000 x smaller

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

Lytic Cycle: Enveloped Virus

1 –Attachment or Adsorption

Viruses…Cycles

2 – Entry by Fusion and Capsid Uncoating

Lytic Cycle: Enveloped Virus

Viruses…Cycles

2 – Entry by Endocytosis and Capsid Uncoating

Lytic Cycle: Enveloped Virus

Viruses…Cycles

3 & 4 –Enveloped VirusReplication & Assembly

Lytic Cycle: Enveloped Virus

Viruses…Cycles

5 – Lysis / Exit by Budding

Lytic Cycle: Enveloped Virus

Viruses…Cycles

Life Cycle of an Enveloped Virus…Lytic

Viruses…Cycles

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

Lytic Cycle: Naked Virus

1 &2–Adsorption and Penetration

Viruses…Cycles

Lytic Cycle: Naked Virus

1 &2 –Adsorption and Injection

Viruses…Cycles

Adsorption and Injection…

Viruses…Cycles

3 & 4 – Replication & AssemblyLytic Cycle: Naked Virus

Viruses…Cycles

5– Release via Cell RuptureLytic Cycle: Naked Virus

Viruses…Cycles

Life Cycle of Naked Virus…Lytic

Viruses…Cycles

Reinfection

As many as 10,000 to 50,000 animal viruses may be produced by a single infected host cell.

Viruses…Cycles

Lysogenic Cycle ~ Replication without Immediate Host Death

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

Neutralization of Viruses by Antibodies

Viruses…Interrupting The Cycle