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CHAPTER 19 BACTERIA AND VIRUSES
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19.2 Viruses I. What is a Virus?
A. Viruses are particles of nucleic acid, proteins, and in some cases lipids. 1. Viruses can reproduce only by infecting living cells. 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.
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19.2 Viruses B. A typical virus is composed of a core of DNA or RNA surrounded by a protein coat. 1. The virus binds to a host and tricks the cell into allowing it inside.
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19.2 Viruses 2. Once inside, the viral genes are expressed and the cell is used to make more viruses. Viruses are highly specific to the cells they infect. C. capsid - a virus’s protein coat.
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Viral Structure Variety of shapes *Helical-spiral *Rod- little sticks
*Spherical- round *Polyhedral- multisided Helical Rod
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Viral Structure spherical polyhedral
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Figure 19-9 Virus Structures
Influenza Virus Tobacco Mosaic Virus T4 Bacteriophage RNA Capsid proteins Head Tail sheath DNA Tail fiber RNA Capsid Surface proteins Membrane envelope
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D. bacteriophages - viruses that infect bacteria.
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19.2 Viruses II. Viral Infection (two types)
A. Lytic infection: a virus enters a cell, makes copies of itself, and causes the cell to burst or lyse.
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Figure 19-10 Lytic and Lysogenic Infections
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19.2 Viruses B. 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.
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19.2 Viruses 1. Lysogenic viruses do not lyse (kill) the cell right away. 2. Instead they may remain inactive for a period of time.
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Figure 19-10 Lytic and Lysogenic Infections
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III. Retroviruses - contains RNA as their genetic information.
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19.2 Viruses A. Get their name because their genetic information is copied backwards. RNA DNA B. Responsible for some types of cancers in humans and also AIDS.
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19.2 Viruses IV. Viruses and Living Cells
A. Viruses are nonliving things. 1. Viruses do not grow, metabolize, or carry out homeostasis.
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19.2 Viruses 2. Yet viruses, after infecting living cells, can reproduce, regulate gene expression, and evolve. B. Because viruses are completely dependent upon living things, it is more likely that viruses evolved after living cells.
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Figure 19-11 Viruses and Cells
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19.3 Diseases Caused by Viruses
I. Bacteria and viruses are everywhere in nature but only a few cause diseases. A. Pathogen = disease-causing agent. B. All viruses reproduce by infecting cells and diseases result when infection causes harm to the host.
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19.3 Diseases Caused by Viruses
IV. Viral Disease in Humans A. Viruses produce disease by disrupting the body’s normal equilibrium.
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Respiratory infections Chickenpox Smallpox
Common Diseases Caused by Viruses Type of Virus Nucleic Acid Disease Oncogenic viruses Retrovirus Adenoviruses Herpes viruses Poxviruses DNA RNA Cancer Cancer, AIDS Respiratory infections Chickenpox Smallpox
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19.3 Diseases Caused by Viruses
B. Viruses attack and destroy certain cells in the body causing symptoms of the disease. C. Viral diseases cannot be treated with antibiotics. D. The best way to protect against most viral diseases is by prevention, often by the use of vaccines before infection.
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