Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Taura syndrome wikipedia , lookup
Elsayed Elsayed Wagih wikipedia , lookup
Human cytomegalovirus wikipedia , lookup
Marburg virus disease wikipedia , lookup
Canine distemper wikipedia , lookup
Canine parvovirus wikipedia , lookup
Orthohantavirus wikipedia , lookup
Hepatitis B wikipedia , lookup
VIRUSES Viruses Are Not Cells! There are several structural and functional differences between cells and viruses The structural differences include: No nucleus No cell membrane No organelles The functional differences include: Do not grow Do not respire Do not develop Do not reproduce Viral Structure A typical virus is made up of 2 parts: Capsid—a protein coat which enables the virus to bind to a cell Nucleic acid—either DNA or RNA Some viruses have an additional protective coating called an envelope Envelope Capsid Nucleic Acid Replication vs. Reproduction Viruses do not reproduce Viruses replicate Reproduction requires cell division A virus requires a host for it to replicate A host is a living cell that provides all the materials a virus needs to replicate Classification of Viruses Shape: allows viruses to attach to only a few kinds of cells; like two pieces of a jigsaw puzzle Filovirus—has no distinct shape Ebola- Zaire Ebola Virus, has the highest case-fatality rate, up to 90%. Massive blood loss leads to death. Polyhedral virus—multifaceted geometric shape Herpesvirus- (cold sores & shingles) virus lays dormant along nerve fibers Binal virus—has a polyhedral capsid and a helical tail Bacteriophage T4—virus which infects E. Coli; used for molecular biology research Helical virus—tightly coiled DNA or RNA inside a long, narrow capsid Tobacco Mosaic Virus— infects members of nine plant families Classification of Viruses (cont.) Host: another way to classify viruses is based on the type of cell they infect Plant virus Animal virus Bacterial virus—these are also called bacteriophages Infection Cycles There are two different pathways a virus follows when it enters the host cell: Lytic Cycle: the virus enters the host, makes copies of itself and then destroys the cell Lysogenic Cycle: the virus integrates its DNA into the DNA of the host cell so that the virus’s genetic information is copied along with the host cell; unlike the lytic cycle, the virus doesn’t immediately destroy the cell, but instead remains inactive for a prolonged period of time Steps in the Lytic Cycle Bacterial Chromosome Bacteriophage Host Cell Capsid Nucleic Acid Lysis and Release Assembly Attachment LYTIC CYCLE Entry Replication Steps in the Lysogenic Cycle Host Cell Host Cells Continue to Reproduce Attachment Trigger—Viral DNA Activates Entry LYSOGENIC CYCLE Prophage Virus Now Enters Lytic Cycle Prophage Formation Host Cell Reproduction Examples of Diseases Caused by Viruses Retrovirus Contains an RNA core that is replicated by 1st transcribing its RNA into DNA Ex: HIV—the virus that infects white blood cells and causes AIDS 1. RNA & reverse transcriptase enter the host cell 4.Viral DNA produces new viruses 2. Enzymes copy the viral RNA into DNA 3. Viral DNA attaches to cell DNA Viroids and Prions Viroid: No capsid Contains RNA Cause plant diseases Prion: Protein molecule with no RNA or DNA Cause animal diseases (i.e. mad cow disease)