Viruses http www youtube comwatch v Rpj 0

Viruses http: //www. youtube. com/watch? v= Rpj 0 em. EGSh. Q

What is a virus? • Tiny, nonliving particles that can cause disease. Remember the 4 characteristics of life? Grow & Respond to Environment, Made of Cells, Reproduce, Obtain & Use Energy q. 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. • viruses only function is to make copies of itself.

Naming Viruses…. • Often named for the DISEASE they cause or for the tissues they infect. • Examples: HIV (Human Immunodificiency Virus), Measles

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 Ex) Polio Virus Cylindrical Ex) Tobacco Mosaic Virus Spherical Ex) Influenza Virus (Flu) Polyhedral Head w/Tail 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.

Lytic Cycle Animation

Lytic Cycle 1. Attachm ent 2. Entry 3. Replicatio n 4. Assembly 5. Lysis and Release

Lytic Cycle 1. Attachment- virus recognizes & attaches to host cell 2. Entry- viral DNA injected into cell 3. Replication- viral genes & capsids copied 4. Assembly- viral genes put together into protein coats 5. 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 1. Attach ment & Entry 2. Provirus formation 3. DNA Replication 4. Cell Division

Lysogenic Cycle 1. Attachment & Entry 2. Provirus formation: Viral DNA embedded into host cell’s DNA 3. DNA Replication: viral DNA copied along with host DNA 4. Cell Division: Cell divides with viral DNA 5. 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 Bacteri. A • Living, Prokaryotic Cells • Reproduction: • Binary Fission (asexual) • Conjugation (sexual) • Treatments: • Anitbiotics • Vaccines • Causes: • • • Strep Throat Tuberculosis Lyme Disease Bacterial meningitis Tetanus VIRUS • 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