VIRUSES and THEIR RELATIVES VIRUSES and THEIR RELATIVES

Characteristics of Viruses Can Reproduce 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 Non-cellular – no cytoplasm, no cell membrane no metabolism and no movement (without help) no metabolism and no movement (without help) Have Genetic Material Have Genetic Material – Either DNA or RNA

What do viruses infect? Viruses infect Bacteria Viruses infect Bacteria –These viruses are called bacteriophages Viruses infect Plants Viruses infect Plants –One example is the Tobacco Mosaic Virus Viruses infect Animals Viruses infect Animals –One example is the common cold virus Viruses usually infect a specific host including:

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

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

Bacteriophage

How are new viruses produced? How are new viruses produced? The method slightly differs if the virus contains DNA or RNA The method slightly differs if the virus contains DNA or RNA DNA Virus: 1. The viral DNA is injected into the host cell. 2. Viral DNA enters the nucleus and becomes part of the host cell DNA. 3. The host cell produces viral DNA, RNA and proteins and assembles new viruses.

How are new viruses produced? RNA Virus: Retrovirus 1. Retrovirus injects its RNA into the host cell. 2. The viral enzyme- REVERSE TRANSCRIPTASE- converts the viral RNA into DNA. 3. The newly formed DNA gets into the host cell’s DNA and the host cell then produces new RNA and proteins from it.

Relatives of Viruses Viroids Viroids –short strands of RNA (approximately bases) –no capsid –infect plants only Prions Prions –Protein strands of approximately 250 amino acids –Abnormally fold –Do not denature (lose shape) easily –Interfere with brain structure and nerve cell function

VIROIDS PRIONS

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

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

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

VACCINES preventions…not a cure Injection of a non-replicating form of a virus. Injection of a non-replicating form of a virus. Causes the body’s immune system to produce proteins called antibodies. Causes the body’s immune system to produce proteins called antibodies. Antibodies bind to viruses and “flag” them so immune cells can destroy them or prevent viruses from invading a host cell. Antibodies bind to viruses and “flag” them so immune cells can destroy them or prevent viruses from invading a host cell. Antibodies continue to be produced indefinitely and protect in the event of a second exposure to the real disease causing virus. 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. 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!

Magic Johnson’s Announcement Magic Johnson’s Announcement

AIDS and HIV AIDS stands for Acquired Immune Deficiency Syndrome AIDS stands for Acquired Immune Deficiency Syndrome AIDS is caused by HIV- Human Immune Deficiency Virus 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 (type of white blood cell of the immune system) receptors called CD4. –HIV binds to CD4 and injects its RNA into a host cell –Reverse transcriptase converts the virus RNA into DNA. –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. When the immune system cannot control HIV, the T cell # falls. AIDS is when the T cell count falls below 200/mL of blood. AIDS is when the T cell count falls below 200/mL of blood. A normal T cell count is /mL. A normal T cell count is /mL. AIDS patients die of opportunistic infections- Infections that take advantage of a weak immune system. 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. 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. 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. 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. Protease inhibitors- Protease is an enzyme that cuts new HIV proteins into smaller pieces that are then assembled to form new viruses.