Say Hello to My Little Friend Viruses Say Hello to My Little Friend

What is a virus? nucleic acids enclosed in a protein coat Very tiny-smaller than the smallest bacteria

What do they look like? A virus has an inner core of nucleic acid, either RNA or DNA, and an outer protein coat called a capsid. Some relatively large viruses, such as human flu viruses, may have an additional layer, called an envelope, surrounding their capsids.

Bacteria have viruses too A virus that infects a bacterium is called a bacteriophage or phage for short. A phage has a tail structure as well as a capsid.

Viruses have DNA Viral nucleic acid is either DNA or RNA and contains instructions for making copies of the virus. Some viruses have only four genes, while others have hundreds.

Infection Before a virus can replicate, it must enter a host cell. A virus recognizes and attaches to a host cell when one of its proteins interlocks with a molecular shape that is the receptor site on the host cell’s plasma membrane.

Attachment to host cell A protein in the tail fibers of the bacteriophage T4 recognizes and attaches the T4 to its bacterial host cell. In other viruses, the attachment protein is in the capsid or in the envelope.

Attachment is a specific process Each virus has a specifically shaped attachment protein. Therefore, each virus can usually attach to only a few kinds of cells. In general, viruses are species specific, and some also are cell- type specific. For example, polio viruses normally infect only intestinal and nerve cells.

Species Specific The species specific characteristic of viruses is significant for controlling the spread of viral diseases. Can you think of a virus that can cross species?

Some examples of viruses: Influenza Rabies Ebola HIV Polio Measles HPV

Is a virus a living thing? Most biologists consider viruses to be nonliving because they don’t exhibit all the criteria for life. They don’t carry out respiration, grow, or develop. All viruses can do is replicate—make copies of themselves—and they can’t even do that without the help of living cells.

Viruses can not reproduce Viruses need to attach to and infect a host cell in order to replicate. They do not have the machinery required, so they must take over the host cell and force it to make copies of the virus

How do they get in the cell? The virus attaches to the outside of the cell and then either injects it’s genetic material into the cell or is enveloped by the cell and absorbed into the cell in a vacuole which is then burst, releasing the virus.

Two cycles of Replication Lytic and Lysogenic

Lytic cycle The host cell uses its own enzymes, raw materials, and energy to make copies of viral genes that along with viral proteins are assembled into new viruses, which burst from the host cell, killing it.

Lytic Cycle • The new viruses can then infect and kill other host cells.

Lysogenic Cycle

Not all viruses kill the cells they infect Not all viruses kill the cells they infect. Some viruses go through a lysogenic cycle, a replication cycle in which the virus’s nucleic acid is integrated into the host cell’s chromosome.

Cycles combined Therefore, every cell that originates from an infected host cell has a copy of the virus. The lysogenic phase can continue for many years. However, at any time, the provirus can be activated and enter a lytic cycle.

Examples of viruses that have a lysogenic cycle Herpes (simplex I and simplex II) Chicken pox

Release of Virus from the host cell Either lysis, the bursting of a cell, or exocytosis, the active transport process by which materials are expelled from a cell, release new viruses from the host cell. The plasma membrane surrounds the virus, enclosing it in a vacuole that then fuses with the host cell’s plasma membrane. Then, the viruses are released to the outside.

The only reason most of us are alive right now VACCINES The only reason most of us are alive right now

We’ve previously discussed some diseases that are vaccine preventable: Measles Mumps Rubella Polio Influenza HPV Hepatitis B Tetanus Pertussis Diptheria

Starting from the Beginning: Edward Jenner: He is credited with developing the first smallpox inoculation. Noticing that milkmaids who had caught cowpox did not catch the smallpox virus, he would apply a small amount of pus from a sore of someone who had the virus to the arm of an uninfected person, allowing their body to develop an immunity to the virus. Coined the term VACCINE from the name of cowpox: Variolae vaccinae

Jonas Salk Developed the first inactivated polio vaccine. Polio was a worldwide epidemic, with about 20,000 cases/yr in the US. Refused to patent the vaccine-received no profit from it. “There is no patent-could you patent the sun?”

So how do they work? A vaccine works by exposing the body’s immune system to an antigen. Antigens stimulate the production of antibodies by the immune system. The antibodies kill off the virus, and “keep a record” of the antigen that they had to fight off. If the immune system is exposed to the antigen again, it will recognize and destroy the virus with it’s ready and waiting antibodies.

But won’t it make you sick?! Vaccines do have side effects, yes, but they are designed in such a way to be safe. There are multiple different kinds of vaccines, and all of them involve weakening, killing, modifying or isolating parts of the virus. Due to these alterations, the virus in the vaccine is not able to cause the disease that it will cause the immune system to develop antibodies for.

Types of vaccines Live attenuated Inactivated Vaccines http://www.vaccines.gov/more_info/types/i ndex.html Live attenuated Inactivated Vaccines Subunit Vaccines Toxoid Vaccines Conjugate Vaccines DNA Vaccines Recombinant Vector Vaccines