Viruses and Prokaryotes
Chapter 20.1-20.3
Difference between
Bacteria and Viruses
A virus is a strand of DNA or RNA
surrounded by a protein coat
(CAPSID)
Viruses are not considered to be
alive!!
Bacteria are one-celled
microorganisms
BOTH ARE INFECTIOUS!
Any disease-causing agent is known
as a PATHOGEN
Viral Structure
Structure: genetic material
surrounded by a capsid
(protein shell).
Different shapes and sizes
Capsids surrounded by lipid
envelope or protective outer
coat
Why aren’t Viruses Alive?
CAN ONLY REPRODUCE
BY INFECTING OTHER
LIVING CELLS
How do viruses enter cells?
Viruses enter host cells in various ways
Eukaryotic viruses fuse with host cell membrane
Eukaryotic viruses enter through endocytosis
When virus is taken in through endocytosis, the
virus is now able to reproduce.
Lytic Infection
host bacterium
Viruses cause two
types of infections:
First Type:
LYTIC: causes host
cell to burst, or lyse
The bacterophage attaches
and injects it DNA into a
host bacterium.
The host bacterium breaks
apart, or lyses. Bacteriophages
are able
to infect new host cells.
The viral DNA directs the host
cell to produce new viral parts.
The parts assemble into new
bacteriophages.
The viral DNA
forms a circle.
Lysogenic Infection
Second Type:
The viral DNA is called a prophage
when it combines with
the host cell’s DNA.
LYSOGENIC: does
no immediate harm
Prophage: phage
DNA that is inserted
into host cell DNA
Many cell divisions produce a
colony of bacteria infected
with prophage.
Although the prophage is not
active, it replicates along with
the host cell’s DNA.
Bacteriophages
Viruses that infect
bacteria
capsid
DNA
ex: T-bacteriophage,
which infects E. coli
bacteria
Pierce host cells and
inject their DNA into
viral hosts
tail sheath
tail fiber
Prokaryotes
• Unicellular organisms that lack a nucleus
• DNA not membrane bound and is located in cytoplasm
• Either ARCHAEA or BACTERIA
Bacteria
• Wall protection
• Flagella
• Peptidoglyclan
cell wall
(polymer of
sugars and
amino acids)
Archaea
• Walls lack peptidoglycan
• More like eukaryotes than
bacteria genetically
• Live in extreme
environments (salty, hot,
methane-rich)
Great Salt Lake
Prokaryote Structure and
Function
• Prokaryotes vary in:
• Size
• Shape
• Mode of movement
• Way obtain and release energy
Size, Shape, and
Movement
• Shapes: Bacilli, cocci, spirilla
• Bacilli: rod shape
• Cocci: spherical
• Spirilla: spiral, coiled
Energy Used by Prokaryotes:
Nutrition & Metabolism
• Heterotroph: take in nutrients
• Photoheterotroph: use light energy and take in
nutrients
• Photoautotroph: use light energy to convert carbon
dioxide into carbon compounds
• Chemoautotroph: use energy released by chemical
reactions to make food
Energy Released by
Prokaryotes
Growth and Reproduction in
Prokaryotes
• Reproduce by BINARY FISSION
(asexual)
• When growth conditions are
unfavorable, prokaryotic cells form
an ENDOSPORE (thick, internal
wall that encloses the DNA)
Recombination in
Prokaryotes
• Mutations: cause prokaryotes to
evolve
• Conjugation: exchange of genetic
information when a hollow bridge
forms between 2 bacterial cells and
genetic material (plasmid) moves from
one cell to the other.
Importance of Prokaryotes
• Decomposers
• Producers
• Nitrogen fixers
• Food production
• Drugs and antibiotics
What is a Pathogen?
Microorganisms (viruses and
bacteria) that cause disease
Bacterial Pathogens
• Bacteria cause disease by destroying living cells or by
releasing chemicals that upset homeostasis
• Damage host tissue
• Release toxins
Methods for controlling bacteria: removal,
disinfectants, food storage and processing,
sterilization by heat, vaccines, and antibiotics!
What is the Benefit of a
Vaccine?
Vaccines are made from weakened pathogens and
stimulates the body’s OWN immune response
Immune system gets MEMORY of pathogen
Made from killed or weakened microbes or certain
parts of microbes
Viral Diseases
• Viruses cause disease by directly destroying living
cells or by affecting cellular processes in ways that
upset homeostasis
Viral Diseases
Some can be prevented with vaccines
Examples of Viral Infections:
Cold
Influenza
SARS
HIV
Mono
Rabies
Smallpox
Common Cold
> 200 different viruses
cause cold symptoms
each season
High mutation rate
Symptoms last between
5-7 days
Influenza
Why is the spread difficult to control?
FLU virus
Spreads quickly, causes local epidemics
20% of American population infected with flu virus per
year
Different types of flu viruses affect different species
H1N1 (Swine Flu/Spanish Flu of 1918)
Others infect pigs, birds, horses, etc.
SARS
Severe Acute Respiratory Syndrome
Coronavirus: cause respiratory or enteric infections
8096 infected and 774 deaths from 11/2002-7/2003
Symptoms: Fever, GI problems, cough, sore throat,
shortness of breath
HIV/AIDS
Human Immunodeficiency Virus
Lysogenic and Lytic Infection
Retrovirus: contain RNA and uses reverse
transcriptase enzyme to make DNA (RNADNA)
Viral DNA enters host nucleus and incorporates itself
into host DNA strand and remains dormant for years
When active, however, new viral parts are made,
viruses bud or lyse through host cell and infect other
host cells.
Mononucleosis
Caused by Epstein-Barr Virus (EBV)
Same family as the Herpes Virus
Has a lytic and a latent cycle
Increases WBCs in bloodstream
Symptoms: severe fatigue, sore throat
In US, 95% of adults 30-40 years old have
antibodies against EBV
Rabies
Causes acute encephalitis (swelling of the brain)
Most commonly transmitted through bites from
animals infected with the virus
Virus travels to the brain via peripheral nerves
Once symptoms begin to show (usually after a few
months), the disease is usually fatal.
IF BITTEN BY RABID ANIMAL: need 4 doses of
Rabies Vaccine and 1 dose of Human Rabies
Immunoglobulin
Smallpox
Unique to humans
Found in blood vessels of skin,
throat, and mouth
In 18th century, virus killed
400,000 Europeans; During
20th century, virus killed 300500 million people throughout
the world
Vaccine available
As of NOW, Smallpox is the
only infectious disease to be
completely eradicated.
What is a Viroid?
Infectious particle
Cause disease in plants
Passed through seeds or
pollen
Made only of singlestranded RNA
What is a Prion?
ALSO Infectious
Proteins that can cause other
proteins to fold incorrectly
Infections BUT contain NO
GENETIC MATERIAL!
Mad Cow Disease
degeneration in the brain
and spinal cord