Viruses Doesn’t belong to any kingdom -It’s not a plant or an animal. -It’s not a fungi, protist, or bacteria. WHAT IS A VIRUS?

A virus is an infectious agent made up of nucleic acid (DNA or RNA) wrapped in a protein coat called a capsid. Viruses have no nucleus, no organelles, no cytoplasm or cell membrane—Non-cellular vs

Viruses have either DNA or RNA but NOT both. Viruses are parasites—an organism that depends entirely upon another living organism (a host) for its existence in such a way that it harms that organism. HIV Infected Cell (This is the reason why HIV is so incurable.) A flea is a parasite to a dog and is harmful to the dog.

Virus Living Cell RNA or DNA core (center), protein coat (capsid) Cell membrane, cytoplasm, genetic material, organelles Structure Copies itself only inside host cell--REPLICATION Asexual or Sexual Reproduction DNA and RNA Genetic Material DNA or RNA Growth and Development NO YES—Multicellular Organisms Obtain and Use Energy NO YES Response to Environment YES NO Change over time NO YES

Are viruses living? NO ONE How many characteristics of life do viruses possess? ONE *Genetic Material Are viruses living? NO

Human Diseases Caused by Viruses: Warts common cold Influenza (flu) Smallpox Ebola Herpes AIDS Chicken pox Rabies Viruses can be prevented with vaccines, but NOT treated with antibiotics. (antibiotics treat bacteria)

List of Vaccine-Preventable Diseases Mumps Pertussis Pneumococcal Anthrax Cervical Cancer (Human Papillomavirus) Diphtheria Hepatitis A Hepatitis B Haemophilus influenzae type b (Hib) Human Papillomavirus (HPV) Influenza (Flu) Japanese encephalitis (JE) Measles Meningococcal Mumps Pertussis Pneumococcal Polio Rabies Rotavirus Rubella Shingles (Herpes Zoster) Smallpox Tetanus Typhoid Tuberculosis (TB) Varicella (Chickenpox) Yellow Fever

Certain viruses can only attack certain cell types Certain viruses can only attack certain cell types. They are said to be specific. Example: The rabies virus only attacks brain or nervous cells. Surface Markers Virus Receptor Sites It’s like the pieces of a puzzle. The ends have to match up so only certain pieces fit. Cell

A virus recognizes cells it can infect by matching its surface marker with a receptor site on a cell. Virus Surface Markers Cell Receptor Sites

The Lytic Cycle A virus CANNOT reproduce by itself—it must invade a host cell and take over the cell activities, eventually causing destruction of the cell and killing it. (The virus enters a cell, makes copies of itself and causes the cell to burst releasing more viruses.) DNA/RNA is copied. DNA/RNA injected into cell. Virus attaches to cell. Step 3 Step 2 Step 1 Virus copies itself. Cell bursts (lyses) and releases new viruses. Step 4 Step 5

Even 2,500 Years Ago, People Knew Immunity Worked. Greek physicians noticed that people who survived smallpox never got it again. The insight: Becoming infected by certain diseases gives immunity.

How does vaccination work? A live or inactivated virus (Antigen) capable of producing an immune response in a person is given. This signals the production of antibodies to fight future virus attacks.

It works like this Patient exposed to pathogen Carrying antigens A and B Molecular Biology of the Cell Alberts et al

Bacteriophage—viruses that infect bacteria Capsid (protein coat) inside contains either RNA or DNA 2. Flu (influenza), HIV DNA or RNA Surface Marker Capsid (protein coat)

Amoeba sisters https://www.youtube.com/watch?v=PHp6iYDi9ko