VIRUSES and THEIR RELATIVES

Characteristics of Viruses Can Reproduce Not by mitosis or meiosis Only when associated with another cell Called Obligate Intracellular Parasites – microorganisms that can only reproduce if they have entered another organism's cell Non-cellular no cytoplasm, no cell membrane, no metabolism and no movement (without help) Have Genetic Material Either DNA or RNA

What do viruses infect? Bacteria These viruses are called bacteriophages Plants One example is the Tobacco Mosaic Virus Animals One example is the common cold virus

Virus Structure Lots of Variety! 3 Main Parts: DNA/RNA Capsid (protein coat) Spikes

Enveloped Viruses Viruses which have a membrane surrounding the protein coat or capsid. These viruses generally infect animals.

Bacteriophage

How are new viruses produced? The method slightly differs if the virus contains DNA or RNA DNA Virus: 1. The virus attaches to the host cell and enters. 2. The capsid is removed and the viral DNA goes through replication, transcription and translation to make new viral proteins. 3. New viruses are assembled in the host cell. 4. New viruses break out of the host cell, destroying it in the process.

Magic Johnson’s Announcement

AIDS and HIV AIDS stands for Acquired Immune Deficiency Syndrome AIDS is caused by HIV- Human Immune Deficiency Virus HIV is a retrovirus which means that it has RNA as its genetic material. The targets of HIV are the helper T cell receptors called CD4. Helper T cells are a type of white blood cell. HIV binds to CD4 and injects its RNA into a host cell.

AIDS and HIV continued… Reverse transcriptase is an enzyme that converts the virus RNA into DNA. The viral DNA gets into the host cell DNA and the cell makes new viruses from it. The newly formed viruses poke holes in the host cell’s membrane and break out of the cell. THIS DESTROYS THE T CELLS!

HIV to AIDS Transition When the immune system cannot control HIV, the T cell # falls. AIDS is when the T cell count falls below 200/mL of blood. A normal T cell count is 500-1000/mL. AIDS patients die of opportunistic infections- Infections that take advantage of a weak immune system.

HIV – TIME COURSE TO AIDS

HIV Treatments Reverse Transcriptase inhibitors- Prevent HIV RNA from being turned in to DNA. Integrase inhibitors- Integrase is an enzyme that allows the HIV DNA to get incorporated into the host cell’s DNA. Entry inhibitors- Blocks the CD4 receptor. Protease inhibitors- Protease is an enzyme that cuts new HIV proteins into smaller pieces that are then assembled to form new viruses.

VACCINES preventions…not a cure Injection of a non-replicating form of a virus. Causes the body’s immune system to produce proteins called antibodies. Antibodies bind to viruses and inactivate them by covering their spikes. Antibodies also “flag” them so immune cells can destroy them.

Antibodies continue to be produced indefinitely and protect in the event of a second exposure to the real disease causing virus. Immunity – Being protected from the symptoms of a recurring virus due to antibodies previously produced. YOU ARE NOT PROTECTED FROM ANOTHER INFECTION…just the symptoms!

Relatives of Viruses Prions Protein strands of approximately 250 amino acids Abnormally fold Do not denature (lose shape) easily Interfere with brain structure and nerve cell function

Prion Disease: MAD COW DISEASE (Bovine Spongiform Encephalitis) Mid 1980s epidemic in UK Meat and bone products fed to cattle (including brain)- sheep with scrapies By 2010, 184,000 cases in UK alone Recent case in California

Creutzfeldt-Jakob Disease Mad Cow Disease in humans Get from eating meat, especially products that could contain brain parts (hot dogs, ground beef, etc.) USDA requires that all brain and spinal cord materials be removed from high-risk cattle

People of New Guinea CJD epidemic in mid 1900s Funeral rituals More prevalent in women and children- cleaned and processed bodies and got the “leftover” parts to eat