Viruses THE MICROSCOPIC MENACE Viruses are Pathogens Viruses

Viruses THE MICROSCOPIC MENACE

Viruses are Pathogens Viruses are incredibly abundant and can cause disease in not only humans, but all living organisms including plants, fungi, and even bacteria.

FIRST THINGS FIRST! Viruses Are Not Alive! Viruses do not have the characteristics of life and are not considered alive. Viruses do not respond to their environment. Viruses do not grow. Viruses do not require energy Viruses cannot reproduce on their own and must reproduce in a host cell.

Virus Structure Viruses are composed of a protein coat and a piece of genetic material (DNA or RNA) The surface of the virus is covered in antigens

Antigens Protein Coat Viral DNA

Learning Check Make a t-chart showing the differences between bacteria and viruses Bacteria Viruses

INFLUENZA a. k. a The Flu The Influenza Virus affects respiratory systemthe nose, throat, and lungs. Symptoms: Fever, aching muscles, headache, cough, nasal congestion, and fatigue. Although it usually passes, it can be deadly depending on the strain of the virus. Young children and older adults have a higher risk of facing complications from the flu.

The Flu Pandemic of 1918 In 1918, a strain of flu virus carried by American soldiers to Europe during WWI became the deadliest flu in human history. Infected over 500 million people Killed as many as 100 million worldwide.

Human Immunodeficiency Virus a. k. a HIV infects T-cells and other white blood cells, causing a failure of the immune system It can be transmitted sexually or by sharing drug needles. Acquired Immunodefieciency Syndrome (AIDS) results when the virus has weakened the immune system allowing other diseases to infect the body. The virus can be managed with various medications.

Ebola Virus Disease The virus is believed to be carried by African fruit bats and other animals. The Ebola Virus infects macrophages, liver cells, and cells lining the blood vessels Symptoms: Fever, Headache, Diarrhea, Vomiting, and unexpected bleeding Symptoms can appear between 2 -21 days after exposure to the virus. Can be spread by direct contact with bodily fluids and infected objects. Survivors develop antibodies that last for at least 10 years.

HOW DO WE STOP THEM? Viruses are different than bacteria. Bacteria can be killed by antibiotics, such as penicillin, but viruses can’t. Vaccines are injections of weakened or inactive versions of the virus that can be recognized by your immune system. Vaccines kick start your immune system to quickly create antibodies against the virus. Memory cells remember how to create necessary antibodies for the virus. This keeps you safe from future infections.

Remember you cannot destroy viruses with antibiotics!

Viral Replication Viruses replicate by invading a host cell and forcing it to make copies of the virus. This process kills the host cell. 2 types of Viral Replication • Lytic Cycle • Lysogenic Cycle

Lytic Cycle The virus attaches itself to a host cell. The virus injects its DNA into the cell. The viral DNA merges with the host cell’s DNA The viral DNA “hijacks” the cell forcing it to make copies of the viral DNA and viral Proteins. The new viruses assemble and destroy the cell.

Lytic Cycle Viral DNA Release DNA and Proteins

From This To This

Lysogenic Cycle STAR T Virus Attaches and Injects DNA Release Viral DNA Replicates Assembly Cell divides with Viral DNA inside

Lysogenic Cycle The Lysogenic Cycle ends in the same way as the Lytic Cycle. The Lysogenic Cycle is usually longer than the Lytic Cycle. After the viral DNA is injected, the virus waits until it is ready to enter the Lytic Cycle again and kill the cell.

Learning Check #2 Describe the Lytic and the Lysogenic Cycle Lytic Cycle Lysogenic Cycle

1. Virus - non-living, disease-causing particle. 2. Bacteria - single-celled organism without a nucleus. 3. Eukaryote - single or multicellular organism with a nucleus.