VIRUSES: The Ultimate Parasite Virus is Latin for “poison”

Are Viruses Alive? Are NOT cells! They are “lifeless” particles with no metabolic functions of their own They cannot reproduce on their own and need to “infect” other cells They do not display the essential characteristics of life They are considered to be between nonliving and living matter They form parasitic relationships with living organisms’ cells: the virus benefits at the expense of the living organism

Viruses are tiny…even much smaller then bacteria We don’t measure them in µm (microns), but nm (nanometres), which is a billionth of a metre.

Virus Morphology (Form or structure) Viruses are far less complex then the simplest living organism. There basically a piece of DNA or RNA surrounded by a protein coat (or capsid). The protein coat is sometimes surrounded by an envelope containing “spikes” The virus’s spikes enable the virus to attach to the surface of a host cell.

Naked Vs. Enveloped Viruses Viruses get their envelopes from the host’s cells when they infect them.

Bacteriophages (Phages) Tail A type of virus that specifically infects bacteria cells. Phages have a unique “tail” structure they use to help them attach to host cells.

Virus spike attaches to cell receptor Viral Replication The Lytic Cycle: 1st step: Virus spike attaches to cell receptor 2nd step: Virus inserts it’s own genetic material (DNA or RNA) into the host cell Virus Spike Host Cell Receptor

Viral Replication 3rd step: The host cell is tricked into replicating the viral DNA/RNA and producing the other parts of its structure. 4th step: The viruses components are assembled and packaged into full virus particles.

The lytic cycle can happen as quickly as 25 to 45 minutes! Viral Replication 5th Step: Lysis – the destruction or bursting open of a cell Hundreds or even thousands of the new virus particles are released from the infected host cell, killing it in the process The lytic cycle can happen as quickly as 25 to 45 minutes!

Lysogenic Cycle Bacteriophages can also insert their own genetic material into DNA of the bacteria they are infecting The bacteria cells replicate without initially being harmed, as the virus is in a state of dormancy called lysogeny

Once you get herpes, it remains dormant in your body for life Lysogeny Infected bacteria can remain like this until an environmental factor triggers the lytic cycle, once again producing new virus particles Example: Herpes Virus Once you get herpes, it remains dormant in your body for life Environmental factors cause the virus to become active and cold sores to appear

Host Range All viruses need to infect cells to replicate, but they are limited by which cells they can successfully invade. The number of different cells, tissues or species that a virus can infect is called it’s “host range”. Viruses can have broad host range (are able to infect many) or narrow host ranges (infect very few) Example: Rabies Virus can infect many mammals such as rodents, dogs, and humans. Swine Flu can infect pigs and humans. The Human cold virus (rhinovirus) only infects the cells of the upper respiratory tract. HIV (Human immunodeficiency virus) infects the human immune system.