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Viruses Living or Not? Viruses Virus – Latin for “poison” Russian Biologist Dmitri Ivanovski (1892) – Tobacco Mosaic Disease First virus to be discovered, 1930 Virus that affects plants No effect on humans Characteristics of Viruses Among the smallest biological particles (not cells) that are capable of causing disease in living organisms. Virus particles are called VIRIONS 5000 influenza viruses can fit inside the head of a pin! Size of a Virus!~ Here is how you can imagine the size of viruses: If a virus was the size of a basketball: A bacterium would be as large as a city block A grain of sand would be two miles long A person would be 4,000 miles tall Studying the “T4-Bacteriophage Also known as: “eaters of bacteria” have a head and tail region – (serve as the principle experimental object in studying viruses) Check out: http://www.cellsalive.com/ph age.htm Not Considered Living A virus IS NOT a bacteria, fungus, protist, plant or animal. They CAN NOT carry out cellular functions. They do not grow or undergo division A virus can not replicate on their own – they need to infect a host and use the hosts organelles and enzymes to do this! VIRUSES & CELLS Characteristic VIRUS (non-living) CELL (living) Structure DNA or RNA core, capsid Cell membrane, cytoplasm, nucleus, other organelles Reproduction Only within a host Asexual and sexual reproduction Genetic Code DNA or RNA DNA Growth/Dvpmt NO Yes Energy NO Yes Response to Environment No Yes Change over time Yes Yes History of Viruses Invasions, wars, and immigrations can introduce viral diseases to different populations Some viral infections have had major global effects: Influenza type A is believed to be responsible for global flu outbreaks in 1918, 1957 and 1968 16th century Spanish explorers brought small pox, measles and influenza viruses to the New World Viruses - Disease Viral infections generally behave in 2 ways: 1. Viruses reproduce and cause disease immediately (lytic or active) 2. Viruses integrate into the host cell (lysogenic or dormant) Viral Replication – Lytic Cycle Infection http://www.mcgrawhill.ca/school/schoolGraphi cs/biology2_1.mpg Lytic (kills cells dead) Adsorption – attracting and holding other materials or particles on its surface Entry – penetration of the cell Replication – uncoating and replicating Assembly – maturation / prepare to leave Release – leaving the cell How are Viruses Studied? “Virology” is the study of viruses; scientists who study viruses are called Virologists. They use: electron microscopes to visualize viruses; cell cultures to grow viruses (although some viruses will only grow in animals) techniques from molecular biology, genetics, and immunology; proper safety precautions when studying dangerous viruses. What are Viruses Made of? Viruses are composed of nucleic acid, proteins, and sometimes, lipids. They are not very Complex ! The Nucleic acid core, which can be either DNA or RNA, encodes the genetic information to make virus copies. The nucleic acid is surrounded by a protective protein coat, called a capsid. These are called “naked” viruses. An outer membranous layer, called an envelope, made of lipid (bilayer) and protein, surrounds the capsid in some viruses…..these ones are called “enveloped viruses” The capsid accounts for 95% of the total virus, and gives the virus a particular shape Virus Structure Envelope Nucleic acid Capsid How are Viruses Classified? Genetic Material DNA or RNA But not both Capsid Structure Helical (rod shaped) Polyhedral Complex Helical Marburg virus Polyhedral SV40 virus Presence or absence of a membranous envelope surrounding the capsid Complex bacteriophage What organisms and Host cells do Viruses Infect? INFECTION BY A VIRUS: Viruses infect bacteria, plants, animals and other living organisms in order to reproduce. A given virus usually infects a limited number of species Within a host organism, usually only a limited number of cell types are susceptible to infection by a given virus HOST RANGE: Array of host cells that a particular virus can infect The virus needs a partner Determined by a lock-and-key fit between the virus and the receptor on the surface of a host cell. Flu attack: How Viruses Invade Your Body http://www.youtube.com/watch?v=Rpj0emEGShQ What Diseases are Caused by Viruses? Infectious diseases RNA viruses (retroviruses) DNA viruses (mutates more often) (more stable) AIDS Respiratory Disease Influenza (flu) Smallpox Common cold Chickenpox Polio Mononucleosis Measles Cold Sores Cancer How Can Viral Diseases Be Prevented and Treated? Good hygiene Vaccines Avoid contact with contaminated food, water, fecal material or body fluids. Wash hands frequently. Stimulate natural defenses with in the body. Contain a component of or a weakened or killed virus particles. Are developed for many once common illnesses such as smallpox, polio, mumps, chicken pox. Not available for all viruses. Anti-viral drugs (but not antibiotics) Available for only a few viruses. Inhibit some virus development and/or relieve symptoms. How Do New Viruses Emerge? Through mutation and evolution By spreading from one species to a new host species By spreading from an isolated location to more widespread locations Through the detection of previously unrecognized viruses How do Our Bodies Fight Viruses? Function of the Immune System Recognition: Destruction: Antibodies (proteins that bind to the surface of a virus) recognize an infected cell and attach White cells move in to destroy the infected cells Also known as leucocytes that come from the bone marrow Goal is to recognize foreign substances (not healthy cells) Memory: Once infected, memory cells recognize the virus if it enters the cell again HSV1 * vs HSV2 Human Papilloma Virus – 14yo boy (think Tree Man) http://www.youtube.com/watch?v=DStwXsmZ3OE http://www.youtube.com/watch?v=K8v3VzEyp88 Polio Virus Six countries (Afghanistan, Egypt, India, Niger, Nigeria, and Pakistan) still have polio circulating Polio – primarily affects children! Epstein Barr Virus (EBV) – Kissing Disease From the Herpes Family Causes mono 95% of all adults have been infected with EBV Requires intimate contact with the saliva of an infected person – not common in air/blood Linked to rare forms of cancer Salmon http://www.abs-cbnnews.com/global-filipino/world/10/17/11/lethal-european-fishvirus-found-canada VIRUS MINI QUIZ 1. THE PRIMARY FUNCTION OF ALL VIRUSES IS TO ___________________ MINI QUIZ… 2. WHAT IS THE TYPICAL/COMMON VIRUS THAT STUDENTS STUDY WHEN LEARNING ABOUT VIRUSES? MINI QUIZ… 3. IN ORDER FOR A VIRUS TO REPLICATE IT NEEDS TO BE IN A __________ CELL MINI QUIZ… 4. VIRAL REPRODUCTION THAT KILLS THE HOST CELL IS CALLED THE ___________ CYCLE! MINI QUIZ… 5. WHEN VIRAL DNA IS EMBEDDED INTO A HOST CELL’S DNA IT FORMS A _______________ MINI QUIZ… 6. ANOTHER NAME FOR INFLUENZA IS __________ MINI QUIZ… 7. 3 WAYS VIRUSES CAN BE TREATED/PREVENTED ARE…. MINI QUIZ… 8. SCIENTISTS THAT STUDY VIRUSES ARE CALLED _________________ MINI QUIZ… 9. 3 WAYS THAT VIRUSES CAN BE TRANSMITTED ARE…. MINI QUIZ… 10. A VIRUS THAT HAS ONLY A CAPSID SURROUNDING IT’S GENETIC INFORMATION AND NO ENVELOPE IS CALLED A ______________ VIRUS.