Viruses

What is a Virus? Viruses are tiny, non-cellular, infectious agents that invade living cells and take over their machinery to make copies of themselves.

What is a Virus? Viruses are NOT considered living based on the characteristics of life, because they: Do not make/use energy or have any metabolism (they have no organelles) Cannot reproduce on their own Are not made of cells Do not grow/develop on their own

Virus Structure Bacteriophage Capsid – made of protein, Tail Infects bacterial cells MOST IMPORTANT PART Capsid – made of protein, contains the genetic material (DNA or RNA) Tail Tail Fibres- used for attaching to target cell

Virus Structure Influenza HIV ‘The Flu’ Capsid – made of protein, Human Immunodeficiency Virus MOST IMPORTANT PART Capsid – made of protein, contains the genetic material (RNA) Antigens - made of lipids/glycoproteins, help the virus to attack and enter their target Also help the immune system to identify the virus

Viruses Vocab Viruses are obligate parasites – organisms that need to live in/on another being to survive and do not benefit them in any way Host - The organism/cell that a parasite exploits Viruses are pathogens – something that causes disease in the host cell/organism

How Viruses Work Step One – Viruses attach to their specific target cell based on their antigens. This works like a lock and key, so viruses will only affect certain cells.

How Viruses Work Step Two – The virus will inject its genetic information into the host

How Viruses Work Step Three – The cell now starts to make copies of the virus proteins and genetic information Step Four – The different parts of the virus are assembled into full virus copies

How Viruses Work Step Five – The virus causes cell lysis (cell bursting apart) and the virus copies are released

How Viruses Work

Lytic/Lysogenic Cycles Viruses can infect cells in two different ways If a virus enters and immediately causes infection with the 5 steps, it is called the Lytic Cycle

Lytic/Lysogenic Cycles Viruses can infect cells in two different ways If a virus enters and remains dormant/inactive in the DNA before causing infection, it is called the Lysogenic Cycle

Immune Response Your immune system recognizes viruses and bacteria based on their surface antigens Every cell in your body has your specific markers, so anything that looks different is marked by your body as an invader (this is why people need specific organ transplants and also why you can’t receive blood transfusions from everyone)

Immune Response The Immune System protects the body in two ways: Nonspecific Response: Skin, mucus, sweat, tears, and inflammatory response (heat, redness, swelling, and white blood cells) Specific Response: Body makes antibodies which seek out and kill specific antigens

Brace yourself for the next slide!! Immune Response The immune system is incredibly complex which is why it has an entire branch of science called immunology Brace yourself for the next slide!!

Specific Response There are many cells that are responsible for the specific immune response: Macrophages/Phagocytes- Large cells that ‘eat’ the virus/bacteria and show the T Cells and B Cells the antigen to target Helper T Cells – Cells that tell B Cells, Cytotoxic T Cells, and Natural Killer Cells what to do B Cells – Cells that make Plasma Cells and Memory B Cells Plasma Cells – Cells that make antibodies which target the virus/bacteria Memory B Cells- Cells that ‘remember’ the antigen so they can quickly kill the virus/bacteria if it shows up again later Cytotoxic T Cells – Cells that make poison granules to kill the virus/pathogen Natural Killer Cells - Cells that kill any infected or out of control (cancer) cells

Specific Response HIV attacks Helper T Cells which greatly weakens the immune system This is how HIV (the virus) causes AIDS - Acquired Immunodeficiency Syndrome (the disease)

Medication Viruses are very difficult to target with medications because they are not living by our definition of life Antibiotics are medications that are designed to kill living cells so they are useless against viruses

Vaccines Vaccines have been developed for a number of viruses/bacterial infections. A vaccine actually contains weakened or dead viruses that trigger the immune system to start making antibodies which will protect you in the future

Vaccines Currently available vaccines: Keep in mind that not all vaccines are 100% effective Currently available vaccines: DTaP Shingles Hepatitis A, B Tdap HiB Td HPV Varicella (Chickenpox) Influenza (The Flu) Adenovirus Measles, Mumps, Rubella, Varicella Anthrax Meningococcal Japanese Encephalitis MenB Rabies Pneumococcal Conjugate Pneumococcal Polysaccharide Smallpox Typhoid Polio Yellow Fever Rontavirus