Biology 10: Viruses! XThese incredibly small, simple structures must infect living cells…

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Presentation transcript:

Biology 10: Viruses! XThese incredibly small, simple structures must infect living cells…

What is a Virus? XA tiny particle made up of XA tiny particle made up of : nucleic acid (DNA or RNA) a protein coat called a CAPSID Sometimes with an envelope made of lipids, carbohydrates, and proteins.

Viruses can only be seen by electron microscopy (20 to 14,000 nm). Herpes simplex SARS

POLYHEDRAL viruses are many-sided

HELICAL VIRUSES - Capsids are hollow cylinders surrounding the nucleic acid.

ENVELOPED viruses - helical or polyhedral, but are often shapeless

COMPLEX viruses - a head with a tail attached - e.g. bacteriophages

Virus Reproduction: 1.The Lytic Cycle 2.The Lysogenic Cycle (dormancy) 3.Retrovirus (HIV)

The Lytic Cycle: XVirus injects its genetic material into the host cell. XGenetic material enters the nucleus and is inserted into that cell’s DNA.

XThe cell begins to make virus parts XThe parts are assembled and the cell explodes (lysis) releasing more viruses

THE LYTIC CYCLE

The Lysogenic Cycle: XViral genes do nothing at first (dormant) XEach time that cell divides, it will copy the virus DNA too XThen it can enter the lytic cycle and destroy the cell

LYSOGENIC CYCLE

XThis is how viral reproduction appears in ‘Real Life.’

Viruses Very specific for their host Only infect certain types of cells in a particular species. (HOST RANGE)

Retroviruses and how they work: XHave RNA as their genetic material. XCell makes DNA from the RNA (usually cells make RNA from DNA!) XThe new viral DNA is inserted into the cell’s DNA.

XThe cell follows the directions found in the DNA’s code XThe cell makes more viruses and destroys itself (lytic cycle).

HIV is a present day retrovirus.

Is a Virus ALIVE?

Why are Viruses not Considered Living? XThey do not respire, eat, excrete, or grow. XBy itself, a virus can not reproduce. They must have a host.

Which came first… viruses or cells?

Virus Questions Page 312 in your text – Answer questions