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-andmouth 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)
Influenza Virus
Tobacco Mosaic Virus
Tobacco Mosaic Virus
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
Virus Structures
Virus Structure
http://learn.genetics.utah.edu/archive/sars/images/virus_structure.jpg
http://www.agen.ufl.edu/~chyn/age2062/OnLineBiology/OLBB/
www.emc.maricopa.edu/faculty/farabee/BIOBK/T2phage.gif
Bacteriophage –
attack bacteria
Bacteriophage
http://oceanworld.tamu.edu/resources/oceanographybook/Images/Bacteriophage-t4.gif
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iology/200710/images/kerr_ecoli2.jpg
T4 Bacteriophage – virus that attacks
the bacteria E. coli
Lytic and Lysogenic Infections
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
protein coat
Bacteriophage DNA
Bacterial
chromosome
Bacteriophage attaches to
bacterium’s cell wall
Bacteriophage enzyme lyses the
bacterium’s cell wall, releasing
new bacteriophage particles that
can attack other cells.
Lytic Cycle
Bacteriophage injects DNA
into bacterium
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
Bacteriophage DNA
Bacteriophage protein
The Lysogenic Cycle
Bacterial
chromosome
Bacteriophage
DNA
Bacteriophage injects
DNA into bacterium
Bacteriophage DNA
(prophage) can exit the
bacterial chromosome
Lytic
Cycle
Bacteriophage enzyme lyses the
bacterium’s cell wall, releasing
new bacteriophage particles that
can attack other cells
Section 19-3
Lysogenic
Cycle
Bacteriophage DNA
(prophage) may replicate
with bacterium for many
generations
Bacteriophage DNA
forms a circle
Bacteriophage proteins and
nucleic acids assemble into
complete bacteriophage particles
Prophage
Bacteriophage DNA
inserts itself into
bacterial chromosome
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
HIV
http://www.lib.uiowa.edu/hARDIN/MD/pictures22/cdc/948_AID
S02bbb_lores.jpg
http://pathmicro.med.sc.edu/lecture/HIV-color09.jpg
Flu Virus (RNA virus)
Release of new
virus particles
http://www.chm.bris.ac.uk/webprojects2006/Kelly/influenzafigure1.jpg
attachment to a host cell
• 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
Mad Cow Disease
Virus or Prion
Comparing Viruses and Living Cells
Prokaryotes
Unicellular organisms that lack a nucleus
smallest of all the cells
Common term - Bacteria
Biology4kids
Concept Map
Section 19-1
Bacteria
are classified into the kingdoms of
Eubacteria
Archaebacteria
include a variety of
lifestyles such as
Living in soil
Infecting large
organisms
live in harsh
environments such as
Thick mud
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
Disease
Pathogen
Prevention
Tooth decay
Streptococcus mutans
Regular dental hygiene
Lyme disease
Borrelia burgdorferi
Protection from tick bites
Tetanus
Clostridium tetani
Current tetanus vaccination
Tuberculosis
Mycobacterium tuberculosis
Vaccination
Salmonella food poisoning
Salmonella enteritidis
Proper food-handling practices
Pneumonia
Streptococcus pneumoniae
Maintaining good health
Cholera
Vibrio cholerae
Clean water supplies
B. Structure of a Eubacterium
Peptidoglycan
Cell
wall
Flagellum
Ribosome
Cell membrane
DNA
Pili
C. Identifying Prokaryotes
1. 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
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
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
What type of Prokaryote
survives in this
environment?
Could a photoheterotroph
survive in this environment?
Volcanic Ocean Vent
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 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 N2 converted to NH3
(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
•Required to make proteins
•most of the nitrogen is in the air as N2
N2 in Atmosphere
NH3
NO3and NO2-
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 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