Viruses http://www.youtube.com/watch?v=Rpj0emEGShQ

Viruses Warmup What is a capsid?

What is a virus? Tiny, nonliving particles that can cause disease. Viruses only function is to cause disease and inject genetic information Remember the 4 characteristics of life? Grow & Respond to Environment, Made of Cells, Reproduce, Obtain & Use Energy

Viruses are NOT considered to be a living organism because: They DO NOT reproduce on their own. They must be inside a living cell called the host cell.

What is a virus? Oftened named for the disease they cause or for the tissue the infect Ex. bacteriophage rabies virus adenovirus

Viral Structure Basic structure includes: Nucleic Acid Core Capsid (Protein Coat) Viral Envelope (found in some viruses)

Nucleic Acid Core Contains genetic material which is either DNA or RNA The DNA or RNA is only instructions for making copies of the virus—nothing else.

Viral Shapes are determined by the capsid. Polyhedral Cylindrical Spherical Polyhedral Head w/Tail Ex) Polio Virus Ex) Tobacco Mosaic Virus Ex) Influenza Virus (Flu) Ex) Bacteriophage

Bacteriophage Virus that infects bacteria. Bacteriophages can infect E. coli bacteria making it harmful to humans.

Importance of Shape Allows virus to recognize and attach to specific host cell. The shape is important in viral reproduction because it allows them to invade a host cell. Some are species specific. Can only infect certain species like a bacteriophage only infects bacteria. Some are also cell-type specific. Polio virus infects only human nerve cells.

Attachment and Entry

Viral Infection Once inside the host cell, 2 different processes may occur. Some replicate immediately, killing the host cell. (Lytic Cycle) Others replicate in a way that does not kill the host cell immediately. (Lysogenic Cycle) Let’s take a closer look…

Lytic Cycle In a lytic infection , a virus enters a cell, makes copies of itself, and causes the cell to burst (or called lyse).

Lytic Cycle Animation

Lytic Cycle Attachment Entry Replication Assembly Lysis and Release

Lytic Cycle Attachment- virus recognizes & attaches to host cell Entry- viral DNA injected into cell Replication- viral genes & capsids copied Assembly- viral genes put together into protein coats Lysis and Release- cell bursts & releases viral particles

Lysogenic Cycle Animation

Lysogenic Infection Unlike lytic viruses, lysogenic viruses do not lyse the host cell right away. Instead a lysogenic virus remains inactive for a period of time.

Lysogenic Cycle Attachment & Entry Provirus formation DNA Replication Cell Division Lytic Cycle

Lysogenic Cycle Attachment & Entry Provirus formation: Viral DNA embedded into host cell’s DNA DNA Replication: viral DNA copied along with host DNA Cell Division: Cell divides with viral DNA Lytic Cycle: at any time the viral DNA leaves the host DNA and enters the lytic cycle

Lytic and Lysogenic cycles

Viral Diseases

HIV/AIDS Retrovirus (Viruses that contain RNA as their genetic material) that is lysogenic. Small numbers of HIV viruses bud off from infected white blood cells. They then infect other WBC. But the viruses are not killing the host at this time. HIV turns into AIDs when the virus goes into the Lytic Cycle

Polio virus infects and kills cells of the nervous system, producing paralysis. Human papillomavirus infects cells in the outermost layer of the skin, producing an abnormal growth known as a wart.

Treatment/Prevention Unlike bacterial diseases, viral diseases cannot be treated with antibiotics. WHY?? The best way to protect against most viral diseases is to prevent them with vaccines. Once the viral disease has been contracted, only symptoms of the infection can be treated.

Comparison Living, Prokaryotic Cells Reproduction: Treatments: Causes: BacteriA VIRUS Living, Prokaryotic Cells Reproduction: Binary Fission (asexual) Conjugation (sexual) Treatments: Anitbiotics Vaccines Causes: Strep Throat Tuberculosis Lyme Disease Bacterial meningitis Non-living Reproduction: MUST infect Host Cell Lytic Cycle Lysogenic Cycle Treatments: Symptoms ONLY! Vaccines Causes: Common cold Influenza (Flu) AIDS Warts Hepatitis A, B, C Polio Chicken pox