Presentation on theme: "Viruses. 1.“Virus” is the Latin word for poison. 2. All viruses have one thing in common: They enter living cells and, once inside, use the machinery."— Presentation transcript:
1.“Virus” is the Latin word for poison. 2. All viruses have one thing in common: They enter living cells and, once inside, use the machinery of the infected cell to produce more viruses.
3. A typical virus is composed of a core of DNA or RNA surrounded by a protein coat. 4. A virus’s protein coat is called a capsid. 5. The capsid enables a virus to enter a host cell.
6. Once the viral genes get inside a cell, the genes are expressed. 7. This genetic program causes the host cell to make copies of the virus. 8. In the process, the host cell is destroyed.
9. Most viruses are highly specific to the cells they infect because plant viruses infect plant cells; animal viruses infect only certain related species of animals; and bacterial viruses infect only certain types of bacteria. 10. Viruses that infect bacteria are called bacteriophages.
11. Once a virus is inside the host cell, two processes may occur: the lytic cycle or the lysogenic cycle.
12. In a lytic infection, a virus enters a cell, makes copies of itself, and causes the cell to burst. 13. Because the host cell is lysed and destroyed, this process is called a lytic infection.
14. A lytic virus is like an outlaw in the American Old West because: The outlaw eliminates the town’s existing authority – (host cell’s DNA) The outlaw demands to be outfitted with new weapons, horses, and equipment by terrorizing the local people – (using the host cell to make viral proteins and DNA) The outlaw forms a gang to leave town to attack new communities – (the host cell bursts, releasing hundreds of new viruses)
15. In a lysogenic infection, a virus integrates its DNA into the DNA of the host cell, and the viral genetic information replicates along with the host cell’s DNA.
17. Retroviruses are viruses that contain RNA as their genetic information. 18. Retroviruses get their name from the fact that their genetic information is copied backward, from RNA to DNA. 19. AIDS is the most infamous retrovirus.
20. Viruses rely upon a host to grow and reproduce which means they are parasites. 21. Viruses are not alive although they can reproduce and posses DNA because they do not: 1) grow and develop 2) obtain and use energy 3) respond to the environment
22. No. Most viruses are not harmful to humans. 23. A pathogen is a disease-causing agent. 24. Viruses cause disease by disrupting the body’s normal equilibrium. 25. Viruses attack and destroy certain cells in the body, causing the symptoms of the disease.
26. No. Viral diseases cannot be treated with antibiotics. 27. The best way to protect against most viral diseases lies in prevention, often by the use of vaccines. 28. Most vaccines provide protection only if they are used before an infection begins.