MICR J210 1st Edition Lecture 19Outline of Last Lecture First lecture of this sectionOutline of Current Lecture 1. What are Viruses?2. Reasons to Study Viruses3. Viral Pathogenicity4. Life Cycle of a Virus5. Viral VaccinesCurrent Lecture1. What are viruses? (Structure of a Virus)- What are viruses? o First clue to the discovery of viruses came over 110 years ago (1898), by Loefflerand Frosch who found evidence that the cause of foot-and-mouth disease in livestock was an infectious particle smaller than any bacteriao They were called subcellular form of life that are so small that could not be seen even under a light microscope o They were called Viruses which in Latin means “poisons” or “venoms”- Viruses were visualized only after discovery of electron microscope in 1930 o An individual virus particle is called a VIRION- Viruses are a unique group of infectious agents that differ from living cells in at least three ways:o The presence of either DNA or RNA, not both, in the same viral particle (virion) NOT BOTH!o Their inability to reproduce independently of living cellso They have to infect another organism to survive- Viruses are composed of either RNA or DNA and protein (capsid) which surrounds the nucleic acid. o The combination of the nucleic acid and capsid is referred to as the nucleocapsid o Capside is made of proteins called capsomeres endcoded by either the RNA or the DNAThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- If a virus has only a protein capsid covering it, it is termed a NAKED CAPSID VIRUS or aNAKED VIRUSo A NAKED virus.. The red balls represent the protein subunits that make up the protective covering around the viral genome (DNA in this case). These subunits are called CAPSOMERES and the entire protein coat is called the CAPSID- Some viruses contain an additional component called the envelope which is a membrane derived from host cell o located in the envelope are viral proteinso Enveloped viruses are not very stable since envelope is a biological membrane, e.g. it’s destroyed by stomach acido Enveloped viruses have a lipid-based membrane surrounding the protein capsid.  This envelope is partly composed of the cell membrane within which the virus replicated, and it contains proteins and carbohydrates.  Some of the proteins are from the host cell and some are from the virus.- Genetic makeup of viruses varyo DNA or RNA  Single or double stranded- 4 types of viral genomes are possible; o ss-RNA (single stranded)o ds-RNA (double stranded)o ss-DNA (single stranded)o ds-DNA (double stranded)o Only one type in each virus…never a combo of two different types of nuclear material- Shapes of viral capsid varyo Icosahedral (20-sided: triangles forming interlinked pentamers; most common)o Helical (spiral staircase-shaped)- Viral growth rate o Bacteria divide by binary fissiono 1 Bacterial cell (30 min) = 2 cellso Viruses make separate parts within the host cell they are infecting and then areassembled into many viral particles o 1 Human Virus (12 - 72 hrs) = 100,000 virions Components are made by the host cell and then assembled all at once- Viruses infect all types of living thingso Animal viruses, eg. Influenza viruso Plant viruses , eg. Tobacco mosaic viruso Bacteria viruses, eg. Bacteriophage T4 The viral attachment protein determines the tropism (the types of infections and the types of cells they invade) Emerging infections are starting to cross over into human form2. Reasons to Study Viruses- History has shown that viral diseases have been some of the major concern for epidemics in human;o polio, rabies, smallpox, and yellow fever- Viruses are still the leading cause of all human diseases o Common acute respiratoryo Gastrointestinal infectionso STD: Hepatitis and Herpeso Emerging viruses (cross over from infecting animals or plants and now they are infecting humans)  Ebola virus in Africa, 1976 AIDS virus was discovered in the early 1980 (HIV virus) Hepatitis C virus in 1988 Hantaviruses, associated with infected field mice (1993)  Severe acute respiratory syndrome (SARS, 2003)o The 2003 FIFA Women's World Cup, originally scheduled for China, was moved to the United States. On March 30, the International Ice Hockey Federation (IIHF) cancelled the 2003 IIHF Women's World Championship tournament which was to take place in Beijing.- Useful purposes of viruses for human? Gene Therapyo Can deliver DNA into host cell…take out the pathogenic genes and insert helpful ones-such as clotting factor for a hemophiliac3. Viral Pathogenicity- Effects of viral infection on cells.- Visible effects on the patient (infected individuals); results from;o Direct damage of virus to cells (viral cytopathic effect, CPE) Virus takes over host cell functiono Host defense mechanisms (immunocytopathology) immune system reacts and destroys all viral infected host cell Inflammatory cytokines are the ones responsible for this reactiono Visible effects of viral pathology at the cellular level (cytopathic effect, CPE) Cell death (lysis of host cells): Viral Plaques, Bacteriophage- Viral plaques: no bacteria are present because the area is completely covered in viruses Giant cell formation: Syncytia- Syncytia: fusion of two host cells- Example: HIVo Human Immunodeficiency Virus (HIV )infection in a cell can lead to the formation of "syncytia", which is when cells fuse together to form large cells with many nuclei.  Rounding up of cells (change of function)- Cells that are infected change their function Piling up of cells= transformation= focus formation- Examples: HPV virus causes piling up of cells and forms wartso Warts are small, usually painless growths on the skin caused by a virus (papilloma virus)o The typical wart is a raised round or oval growth on the skin with a rough surfaceo Common warts tend to cause no discomfort unless they are in areas of repeated friction or pressure and often go away on their own within two yearso Venereal warts can cause cancer Inclusion bodies inside the cell (visible by EM)- Inclusion bodies: endosomes that contain viral particles4. Life Cycle of Virus 9 Stepso Recognition Recognize the host cell that has a receptor for its viral attachment protein via cell-specific receptors (Tropism): For example, polio virus can infect the epithelial cells in the