Transcript Viruses
Viruses – Pg 334 new text, Ch. 15 old text Particles that cause infectious disease! What are viruses? The word virus means “poison” in Latin. Viruses can not reproduce on their own and lack other characteristic of living things. They are not living. Viruses replicate through hijacking a host. The structure of viruses Viruses come in all shape and sizes Viruses are tiny! 20nm – 400 nm! Red blood cells are 7500 nm The structure of a virus Protein Capsid (outer casing) Genetic Material (DNA or RNA) o How do Viruses work? A virus enters a cell and instruct it to make more viruses Normal cell activity is affected! Once viruses are replicated the cell burst and the new viruses escape! Viruses replicate in 2 ways. The Lytic cycle where the virus takes over one cell to make more viruses. These are known as virulent phages. The Lysogenic cycle where the virus lies in wait to take over many cells at one time. These are known as temperate phages. Lytic cycle Lysogenic Cycle How do viruses get into the cell? The virus must disguise itself! Viruses are able to disguise themselves with the aid of Marker Proteins. How do Viruses work? Because each virus has a different marker protein, it can only affect certain organisms or cells. Viruses can be different types of the same virus (known as strains) Where are our defences? Cells can produce antibodies which change the chemistry of the capsid and kill infected cells. Vaccines: weakened versions of the virus, harmless and triggers the production of antibodies. Mutations When viruses are replicated the instructions can get mixed up, this is how new strains of viruses are formed! This can change the viruses ability to infect certain cells or even allow it to infect different organisms. Example avian flu! Lytic Cycle 1. 2. 3. 4. 5. Attachment: Bacteriophage attaches itself to the outside of the cell membrane. Entry: Nucleic acid is injected into the cell Replication: When nucleic acid works its way into the cell it destroys the hosts DNA. Then it forces the cell to make more virus material. Formation: The material comes together into new viruses inside of the cell Lysis and release: The viruses break the cell membrane and leave the cell to infect more cells! Lysogenic 1.Attachment: Bacteriophage attaches itself to the outside of the cell membrane. 2.Entry: Nucleic acid is injected into the cell 3.Replication: The Virus DNA works its way into the Hosts DNA. The host cell will then Replicate with the virus DNA as a part of it. This DNA section is known as a provirus. 4.Later the Provirus will be triggered by an outside factor and the virus DNA will take over the new cell.