Viruses Chapter 18

Viruses not alive Come in many shapes and sizes Host-specific: will only “work” in specific types of organisms (bacteria, plant, animal, etc.)

Viral Structures All contain DNA or RNA, protein, sometimes lipids Capsid: protein coat surrounding DNA/RNA Attaches to host cell & “tricks” host cell into allowing virus inside

Viral Infections Once inside a cell, a virus may kill host cell immediately, or over time Viruses containing DNA infect in 2 ways: ●Lytic: kills immediately ●Lysogenic: kills slowly over time

Viral Infections 1) Virus DNA/RNA enters cell 2) Host cell immediately transcribes DNA to mRNA 3) Proteins created attack host cell → shuts down 4) Virus now uses host cell to replicate 5) Host cell eventually bursts, releasing 100s new viruses

Lytic Cycle

Lysogenic Cycle

Chickenpox Chickenpox is a viral infection in which a person develops extremely itchy blisters all over the body. It used to be one of the classic childhood diseases. However, it has become much less common since the introduction of the chickenpox vaccine.

Cold Sores Cold sores — also called fever blisters — are tiny, fluid-filled lesions that occur on and around your lips. Cold sores spread from person to person by close personal contact, such as kissing.

SARS (Severe Acute Respiratory Syndrome) Severe acute respiratory syndrome (SARS) is a serious form of pneumonia. It is caused by a virus that was first identified in 2003. Infection with the SARS virus causes acute respiratory distress (severe breathing difficulty) and sometimes death. When someone with SARS coughs or sneezes, infected droplets spray into the air. You can catch the SARS virus if you breathe in or touch these particles. The SARS virus may live on hands, tissues, and other surfaces for up to 6 hours in these droplets and up to 3 hours after the droplets have dried.

HIV (Human Immunodeficiency Virus) HIV infection is a condition caused by the human immunodeficiency virus (HIV). The condition gradually destroys the immune system, which makes it harder for the body to fight infections.