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
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Bacteriophage – attack bacteria
Bacteriophage
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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 thebacterium’s cell wall, releasingnew bacteriophage particles thatcan 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
Bacterialchromosome
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
Bacterialchromosome
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
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HIV
Flu Virus (RNA virus)
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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 cellsCommon 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 mudLiving in soilAnimal
digestive tracts
Salty lakes Hot springs
A. Classifying Prokaryotes1. Eubacteria – “true bacteria”
common, all around us2. 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
Disease Pathogen Prevention
C. Identifying Prokaryotes1. Shapes• Bacilli – rod shaped• Cocci – spherical• Spirilla – spiral shaped
harmonscience7
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
2. Gram –negative – stain pink or light red, Ex. E. coli
3. Movement
Do they move or how they move?
1.Propelled by flagella2.Spiral forward3.Glide along a layer of excreted slime
C. Obtaining Energy
1.Photoautotroph – photosynthetic prokaryotes (bacteria)
2.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?
Could a photoheterotroph survive in this environment?
E. Releasing Energy -Bacteria use cellular respiration, fermentation or both
1. Obligate Aerobes – need Oxygen (02) to live
2. Obligate Anaerobes - do not need Oxygen (02) and are poisoned by it
botulism
3. Facultative Anaerobes – do not require Oxygen (02) to live, but are not harmed by it either (live in our gut)
F. Growth and Reproduction1.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 NatureA. Decomposers – break down organic
matter
B. Nitrogen Fixers – converts nitrogen into a form plants can us N2 converted to NH3 (ammonia)
• Bacteria in Nature (cont.)C. Bacteria and Disease – 2 ways
1. Damage the tissues to make food2. Release toxins (poisons)
D. Human Uses of Bacteria(yogurt, cheese, mine minerals, oil spill clean up,
medicine etc.)
The Nitrogen Cycle
N2 in Atmosphere
NH3
NO3-
and NO2-
•Required to make proteins
•most of the nitrogen is in the air as N2
H. Controlling Bacteria • Sterilization by heat • Disinfectants • Food Storage and Processing • Antibiotics • Vaccines
Germ Theory – infectious diseases are caused by microorganisms, or germs
Koch’s Postulate1. 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