Viruses & Bacteria 1

A virus is a nonliving particle with a simple structure A virus is a nonliving particle with a simple structure. Composed of a nucleic acid (DNA or RNA) surrounded by a protein coat. Virus that infects bacteria 2

Virus Structure Capsid - The capsid is the protein shell that encloses the nucleic acid; Three functions: 1) it protects the nucleic acid from digestion by enzymes, 2) contains special sites on its surface that allow the virus to attach to a host cell, and 3) Allow virus nucleic acid penetrate the host cell’s membrane and, in some cases, to inject the infectious nucleic acid into the cell's cytoplasm. Envelope - Surrounds the capsid. Composed of two lipid layers interspersed with protein molecules Or RNA Or RNA 3

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Viral Nucleic Acid The nucleic acid of each virus encodes the genetic information for the synthesis of all proteins. Only a few groups of viruses use DNA. Most viruses maintain all their genetic information with the single-stranded RNA. 4

Lytic Cycle The virus attaches to a host cell and injects its nucleic acid into the cell. The viral nucleic acid is immediately replicated, eventually causing the host cell to burst, releasing new viral particles. These new viruses then attack other cells. 5

Lysogenic Cycle After the virus embeds its nucleic acid into the chromosome of the host cell, the viral nucleic acid is replicated along with the host cell’s DNA. Then the virus becomes dormant, sometimes for years without the host knowing. The virus may suddenly become active, resuming the lytic cycle, which will eventually destroy the host cell. 6

Overview: Lytic and Lysogenic cycles 7

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Are viruses alive? Can They: 8 Reproduce? Obtain and use energy? Understanding Viruses Part 1 Can They: Reproduce? Obtain and use energy? Grow, develop, and die? Respond to the environment? 8

Diseases Caused by Viruses Smallpox Ebola Hantavirus Herpes Lassa Fever Mononucleosis West Nile Yellow fever Cancer Influenza Measles Chickenpox Polio HIV Mumps Rabies Hepatitis Common cold 9 Vaccines

Vaccines CLIP Made from parts of a virus. Then when our bodies see the virus again it recognizes and fights the virus. Antibiotics do not work on viruses! Most vaccines contain purified fragments taken from killed bacteria or viruses. Some vaccines contain live viruses, but in a very weak form that dos not cause disease. stimulates the body’s immune response "teach" the immune system how to recognize and fight bacteria and viruses

contagious respiratory illness Influenza contagious respiratory illness 1918 pandemic 20 to 40 million people More people died of influenza in a single year than in four-years of the Black Death Bubonic Plague from 1347 to 1351. Known as "Spanish Flu" or "La Grippe" the influenza of 1918-1919 was a global disaster

Human Immunodeficiency Virus HIV attacks some of the cells that are vital to a healthy immune system, including the white blood cells known as T-helper cells or CD4 cells. AIDS means 'acquired immune deficiency syndrome'. It is a condition that sets in when the HIV virus has killed so many T-helper cells that the immune system is no longer able to recognize and react to attacks from everyday infections.