Presentation on theme: "Viruses Virology - study of viruses Virologist – scientist that studies Viruses."— Presentation transcript:
Viruses Virology - study of viruses Virologist – scientist that studies Viruses
Introduction to Viruses In 1898, Friedrich Loeffler and Paul Frosch: found evidence that the cause of foot-and- mouth disease in livestock was an infectious particle smaller than any bacteria. This was the first clue to the nature of viruses, genetic entities that lie somewhere in the grey area between living and non-living states.
Viruses depend on the host cells that they infect to reproduce. When found outside of host cells, viruses exist as: 1.Protein coat or capsid, sometimes enclosed within a membrane. 2.The capsid encloses either DNA or RNA which codes for the virus elements. In this form outside the cell, the virus is metabolically inert (dormant)
Discovery of Viruses Beijerinck (1897) coined the Latin name "virus" meaning poison for the substance infecting tobacco plants Edward Jenner (1796) developed smallpox vaccine using milder cowpox viruses – the first ever vaccine 1900 Walter Reed showed that an agent so small it could pass through a filter, which trapped bacteria, caused the human disease yellow fever
1918 a pandemic Spanish flu kills 25 million people, more deaths than caused by the first World War Wendell Stanley (1935) crystallized sap from tobacco leaves infected with Tobacco Mosaic Virus (TMV) & found virus was made of nucleic acid & protein Viruses couldn't be seen until electron microscope invented in the 1930s
1950s widespread use of the Salk polio vaccine – killed vaccine 1978 last naturally occurring case of smallpox in the world 1982 recognition of new virus Human Immunodeficiency Virus (HIV-1) 2009 H1N1 Influenza virus – Swine Flu
Characteristics of a Virus Not living organisms Noncellular Consist of a nucleic acid core (DNA or RNA) and a protein coat called the capsid Cannot grow or replicate on their own (inactive particles) Can only reproduce inside of a living host cell using its raw materials & enzymes
Are extremely small particles ranging from 20 - 400 nanometers on average Largest virus is 1000 nanometers in dimension Some can cause disease (smallpox, measles, mononucleosis, influenza, colds, AIDS, Ebola Virus Some may also cause cancers such as leukemias Highly host specific (only infect certain cells) Viruses are classified into 2 main groups by their nucleic acid --- DNA or RNA Viruses
In the lysogenic cycle, the virus reproduces by first injecting its genetic material, indicated by the red line, into the host cell's genetic instructions. In the lytic cycle, the virus uses the genetic material of the host cell to make thousands of copies of its own DNA. The cell bursts and releases the virus particles that infect other cells.
The Lytic Cycle Bacteriophage enzyme lyses the bacterium’s cell wall, releasing new bacteriophage particles that can attack other cells. Bacteriophage proteins and nucleic acids assemble into complete bacteriophage particles Bacteriophage takes over bacterium’s metabolism, causing synthesis of new bacteriophage proteins and nucleic acids Bacteriophage injects DNA into bacterium Bacteriophage attaches to bacterium’s cell wall Bacteriophage Bacteriophage DNA Bacteriophage protein Bacteriophage protein coat Bacteriophage DNA Bacterial chromosome Lytic Cycle
The Lysogenic Cycle Bacteriophage proteins and nucleic acids assemble into complete bacteriophage particles Bacteriophage enzyme lyses the bacterium’s cell wall, releasing new bacteriophage particles that can attack other cells Bacteriophage DNA inserts itself into bacterial chromosome Bacteriophage DNA (prophage) may replicate with bacterium for many generations Bacteriophage DNA (prophage) can exit the bacterial chromosome Bacteriophage DNA forms a circle Bacteriophage DNA Bacterial chromosome Bacteriophage injects DNA into bacterium Prophage Lytic Cycle Lysogenic Cycle Section 19-3
Retroviruses Contains RNA – RNA enters the cells and makes DNA – RNA is copied backward – RNA to DNA (usually DNA to RNA) Virus DNA becomes part of host cell’s DNA Hides in the cell and copies of the virus can be made at any time. Causes some cancers and AIDS
http://pathmicro.med.sc.edu/lecture/HIV-color09.jpg http://www.lib.uiowa.edu/hARDIN/MD/pictures22/cdc/948_AID S02bbb_lores.jpg HIV
Flu Virus (RNA virus) http://www.chm.bris.ac.uk/webprojects2006/Kelly/influenzafigure1.jpg attachment to a host cell Release of new virus particles
Viroid – infect plants, single stranded RNA molecules that have no capsid – disrupt metabolism and destroy plants Prion- contain only protein (no DNA or RNA), forms protein clumps in nervous tissue
Prokaryotes Unicellular organisms that lack a nucleus smallest of all the cells Common term - Bacteria Biology4kids
Section 19-1 Concept Map are classified into the kingdoms of Eubacteria live in harsh environments such as include a variety of lifestyles such as Bacteria Archaebacteria Infecting large organisms Thick mud Living in soil Animal digestive tracts Salty lakes Hot springs
A.Classifying Prokaryotes 1.Eubacteria – “true bacteria” common, all around us 2. Archaebacteria – Ancient Bacteria Extreme environments (hot sulfur springs)
Common Diseases Caused by Bacteria Tooth decay Lyme disease Tetanus Tuberculosis Salmonella food poisoning Pneumonia Cholera Streptococcus mutans Borrelia burgdorferi Clostridium tetani Mycobacterium tuberculosis Salmonella enteritidis Streptococcus pneumoniae Vibrio cholerae Regular dental hygiene Protection from tick bites Current tetanus vaccination Vaccination Proper food-handling practices Maintaining good health Clean water supplies DiseasePathogenPrevention
B. Structure of a Eubacterium Peptidoglycan Cell wall Cell membrane Ribosome Flagellum DNA Pili
2. Cell Walls –made of peptidoglycan Eubacteria – two types of cell walls 1.Gram-positive – stain purple, stains the thick peptidoglycan cell walls Ex. Streptococcus 1.Gram –negative – stain pink or light red, Ex. E. coli 2. Cell Walls –made of peptidoglycan Eubacteria – two types of cell walls 1.Gram-positive – stain purple, stains the thick peptidoglycan cell walls Ex. Streptococcus 1.Gram –negative – stain pink or light red, Ex. E. coli
3. Movement Do they move or how they move? 1.Propelled by flagella 2.Spiral forward 3.Glide along a layer of excreted slime 3. Movement Do they move or how they move? 1.Propelled by flagella 2.Spiral forward 3.Glide along a layer of excreted slime
C.Obtaining Energy 1.Photoautotroph – photosynthetic prokaryotes (bacteria) 1.Chemoautotroph – energy from chemical reactions 3. Heterotroph – obtains energy from food it consumes (organic compounds) 4. Photoheterotroph – photosynthetic and needs organic compounds 1.Photoautotroph – photosynthetic prokaryotes (bacteria) 1.Chemoautotroph – energy from chemical reactions 3. Heterotroph – obtains energy from food it consumes (organic compounds) 4. Photoheterotroph – photosynthetic and needs organic compounds
Volcanic Ocean Vent What type of Prokaryote survives in this environment? What type of Prokaryote survives in this environment? Could a photoheterotroph survive in this environment? Could a photoheterotroph survive in this environment?
E. Releasing Energy -Bacteria use cellular respiration, fermentation or both 1.Obligate Aerobes – need Oxygen (0 2 ) to live 2.Obligate Anaerobes - do not need Oxygen (0 2 ) and are poisoned by it botulism 3.Facultative Anaerobes – do not require Oxygen (0 2 ) to live, but are not harmed by it either (live in our gut)
F. Growth and Reproduction 1.Binary Fission = Asexual – double in size and DNA, split in half. 2.Conjugation = Sexual, two bacteria exchange genetic material – can create a new strain.
F. Growth and Reproduction (cont.) 3.Spore Formation = Endospore -Formed during harsh conditions – hibernates until conditions are good. Ex. Drought, extreme heat, no food, frozen food
Bacteria in Nature A.Decomposers – break down organic matter B.Nitrogen Fixers – converts nitrogen into a form plants can us N 2 converted to NH 3 (ammonia)
Bacteria in Nature (cont.) C.Bacteria and Disease – 2 ways 1.Damage the tissues to make food 2.Release toxins (poisons) D.Human Uses of Bacteria (yogurt, cheese, mine minerals, oil spill clean up, medicine etc.)
The Nitrogen Cycle N 2 in Atmosphere NH 3 NO 3 - and NO 2 - Required to make proteins most of the nitrogen is in the air as N 2
H. Controlling Bacteria Sterilization by heat Disinfectants Food Storage and Processing Antibiotics Vaccines Sterilization by heat Disinfectants Food Storage and Processing Antibiotics Vaccines
Germ Theory – infectious diseases are caused by microorganisms, or germs Koch’s Postulate 1.Pathogen should be found in sick organism 2.Pathogen should be isolated & grown in pure culture 3.Purified pathogens are placed in a new, healthy organism and cause disease in new organism 4.Injected pathogen should be reisolated from second host & be identical to original pathogen