Transcript Chapter 18 Viruses and Bacteria 2

13.1 Ecologists Study Relationships
Chapter 18
Viruses and Bacteria
18.1 Studying Viruses and Prokaryotes
What do you think?
Are viruses alive?
Give evidence to support this opinion:
YES
NO
18.1 Studying Viruses and Prokaryotes
KEY CONCEPT
Infections can be caused in several ways.
18.1 Studying Viruses and Prokaryotes
Viruses, bacteria, viroids, and prions can all cause
infection.
• Any disease-causing agent is called a pathogen.
1 nanometer (nm) = one
billionth of a meter
100 nm
eukaryotics cells
10,000-100,000 nm
viruses
50-200 nm
prokaryotics cells
200-10,000 nm
viroids
5-150 nm
prion
2-10 nm
18.1 Studying Viruses and Prokaryotes
• A virus is made of DNA or RNA and a protein coat.
– non-living
pathogen
– can infect many
organisms
• A viroid is made only
of single-stranded
RNA.
– causes disease in
plants
– passed through
seeds or pollen
18.1 Studying Viruses and Prokaryotes
• A prion is made only of proteins.
– causes misfolding of other proteins
– results in diseases of the brain
18.1 Studying Viruses and Prokaryotes
18.2
Viruses exist in a variety of shapes and sizes.
18.1 Studying Viruses and Prokaryotes
Viruses differ in shape and in ways of entering host
cells.
• Viruses have a simple structure.
– genetic material
– capsid, a protein shell
– maybe a lipid envelope, a protective outer coat
enveloped
(influenza)
capsid
nucleic acid
lipid
envelope
helical
(rabies)
Surface proteins
capsid
nucleic acid
surface
proteins
lipid envelope
polyhedral
(foot-and-mouth
disease)
surface
proteins
capsid
nucleic acid
18.1 Studying Viruses and Prokaryotes
• Bacteriophages infect bacteria.
capsid
DNA
tail sheath
tail fiber
18.1 Studying Viruses and Prokaryotes
• Viruses enter cells in various ways.
– bacteriophages pierce host cells
colored SEM; magnifications:
large photo 25,000; inset 38,000x
18.1 Studying Viruses and Prokaryotes
• Viruses enter cells in various ways.
– viruses of eukaryotes enter by endocytosis
18.1 Studying Viruses and Prokaryotes
• Viruses enter cells in various ways.
– viruses of eukaryotes also fuse with membrane
18.1 Studying Viruses and Prokaryotes
Viruses cause two types of infections.
• A lytic infection causes the host cell
to burst.
host bacterium
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
forms a circle.
The viral DNA directs the host
cell to produce new viral parts.
The parts assemble into new
bacteriophages.
The virus may enter the
lysogenic cycle, in which the
host cell is not destroyed.
18.1 Studying Viruses and Prokaryotes
Stages of the Lytic Cycle
• Event 1 – The bacteriophage attaches and injects its
DNA into a cell.
• Event 2 – The viral DNA forms a circle
• Event 3 – The viral DNA directs the host cell to produce
new viral parts that assemble into new bacteriophages.
• Event 4 – The host bacterium breaks apart and
bacteriophages are able to infect new host cells.
• Final Outcome- The virus destroys the host cells.
18.1 Studying Viruses and Prokaryotes
• A lysogenic infection does no immediate harm.
The prophage may leave the
host’s DNA and enter the
lytic cycle.
The viral DNA is called a prophage
when it combines with
the host cell’s 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.
18.1 Studying Viruses and Prokaryotes
Stages of the Lyogenic cycle
• Event 1 – The bacteriophage attaches and injects its
DNA into a cell.
• Event 2 – The viral DNA forms a prophage by combining
with the host cell’s DNA
• Event 3- The prophage replicates along with the host
cell’s DNA
• Event 4 – Many cell divisions produce a colony of cells
infected with the virus
• Final Outcome – The prophage may leave the host’s
DNA and enter the lytic cycle or may continue to
incubate in the host’s cells.
18.1 Studying Viruses and Prokaryotes
18.3
Some viral diseases can be prevented with vaccines.
18.1 Studying Viruses and Prokaryotes
Viruses cause many infectious diseases
• There are many examples of viral infections.
– common cold
18.1 Studying Viruses and Prokaryotes
Viruses cause many infectious diseases
• There are many examples of viral infections.
– common cold
– influenza
18.1 Studying Viruses and Prokaryotes
Viruses cause many infectious diseases
• There are many examples of viral infections.
– common cold
– SARS
– influenza
18.1 Studying Viruses and Prokaryotes
Viruses cause many infectious diseases
• There are many examples of viral infections.
– HIV (Human
Immunodeficiency
Virus)
– A retrovirus, it copies it
genetic material
“backwards”.
– Destroys host’s white
blood cells
– HIV mutates very
quickly, makes it a
challenge to treat
HIV-infected
white
blood cell
18.1 Studying Viruses and Prokaryotes
Vaccines are made from weakened pathogens.
• Vaccines contain weakened virus or parts of a virus that
it is suppose to protect against.
• Doesn’t cause illness in organism.
• A vaccine stimulates the body’s own immune response.
• Vaccines prepare the immune system for a future attack.
• Vaccines are the only way to control the spread of viral
disease.
18.1 Studying Viruses and Prokaryotes
How to avoid getting and spreading the flu virus
Wash your hands often
Get plenty
Of rest
Drink lots of water
Get a flu shot
Avoid sick people
Eat healthy foods
Like fruits and
vegetables
18.1 Studying Viruses and Prokaryotes
How do viruses and cells compare?
Reproduction:
Viruses- only reproduce with a host cell
Cell- independent cell division
Genetic Code:
Virus- DNA or RNA
Cell- DNA
Growth and Development:
Virus- no
Cell- yes, cells increase in
size and number
18.1 Studying Viruses and Prokaryotes
Obtain and Use Energy:
Virus- no
Cell- yes
Respond to the environment:
Virus- no
Cell- yes
Change over time:
Virus- yes
Cell- yes
18.1 Studying Viruses and Prokaryotes
What do you think?
Are viruses alive?
Give evidence to support this opinion:
YES
NO
18.1 Studying Viruses and Prokaryotes
Bacteria
sections 18.4 – 18.6
18.1 Studying Viruses and Prokaryotes
18.4
Bacteria and archaea are both single-celled
prokaryotes.
18.1 Studying Viruses and Prokaryotes
Bacteria
-Bacteria (prokaryotes) are widespread on Earth.
-They are an important part of communities in which we live.
-Make up the Domains of Archaea and Bacteria
-Grouped based on their need for oxygen.
• Prokaryotes can be grouped by their need for oxygen.
– obligate anaerobes
are poisoned by
oxygen
– obligate aerobes
need oxygen
– facultative aerobes
can live with or
without oxygen
18.1 Studying Viruses and Prokaryotes
General Characteristics of Bacteria
•
•
•
•
Archaebacteria
prokaryote
cell wall – no
peptiodoglycan
unicellular
autotrophic or
heterotrophic
•
•
•
•
Eubacteria
prokaryote
cell wall – has
peptiodoglycan
unicellular
autotrophic or
heterotrophic
18.1 Studying Viruses and Prokaryotes
Bacteria and archaea are structurally similar but have
different molecular characteristics.
• Bacteria commonly come in three forms.
– rod-shaped, called bacilli
– spiral, called spirilla or spirochetes
– spherical, called cocci
Lactobacilli: rod-shaped
Spirochaeta: spiral
• Archaea have many shapes.
Enterococci: spherical
18.1 Studying Viruses and Prokaryotes
• Bacteria and archaea have similar structures.
– plasmid
– flagellum
pili
plasma
– pili
membrance
chromosome
cell wall
plasmid
This diagram shows the typical structure
of a prokaryote. Archaea and bacteria
look very similar, although they have
important molecular differences.
flagellum
18.1 Studying Viruses and Prokaryotes
• Bacteria and archaea have molecular differences.
– The amount of peptidoglycan within the cell wall can
differ between bacteria
GRAM NEGATIVE
GRAM POSITIVE
– Archaea have different lipids entirely
18.1 Studying Viruses and Prokaryotes
• Gram staining identifies bacteria.
– stains polymer peptidoglycan
– gram-positive stains purple, more peptidoglycan
– gram-negative stains pink, less peptidoglycan
Gram-negative bacteria have a thin layer of
peptidoglycan and stain red.
Gram-positive bacteria have a thicker
peptidoglycan layer and stain purple.
18.1 Studying Viruses and Prokaryotes
Bacteria have various strategies (plans) for survival.
Conjugation
• In conjugation, genetic
material transfers between
prokaryotes.
• DNA passes through a
structure called a
conjugation bridge which
connects the cells.
Formation of Endospores
• When conditions are very
bad for growth and
survival, some bacteria
may survive by forming
endospores.
• Endospores can last for
hundreds of years.
conjugation
bridge
TEM; magnification
6000x
18.1 Studying Viruses and Prokaryotes
KEY CONCEPT
Prokaryotes perform important functions for
organisms and ecosystems.
18.1 Studying Viruses and Prokaryotes
Beneficial Roles of Prokaryotes
Prokaryotes provide nutrients to humans and other animals.
Bacteria are important parts of animal digestive system.
-Bacteria benefit from a stable home and source of
food.
-Host animal benefits because the bacteria help break
down foods and produce vitamins and other nutrients.
18.1 Studying Viruses and Prokaryotes
Bacteria are important to human nutrition because they are
used to make many common foods.
• Bacteria help ferment
many foods.
– yogurt, cheese
– pickles, sauerkraut
– soy sauce, vinegar
18.1 Studying Viruses and Prokaryotes
Prokaryotes play important roles in ecosystems.
• Prokaryotes have many functions in ecosystems.
– photosynthesize
– recycle carbon, nitrogen,
hydrogen, sulfur
– fix nitrogen
18.1 Studying Viruses and Prokaryotes
• Bioremediation uses prokaryotes to break down
pollutants.
– oil spills
– biodegradable materials
18.1 Studying Viruses and Prokaryotes
18.6
Understanding bacteria is necessary to prevent
and treat disease.
18.1 Studying Viruses and Prokaryotes
Some bacteria cause disease.
• Bacteria cause disease by invading tissues or making
toxins.
• A toxin is a poison released by an organism.
18.1 Studying Viruses and Prokaryotes
Bacterial Diseases and Antibiotics
Some Bacteria can cause disease in plants and animals.
Bacteria can cause illness in 2 basic ways.
1. Bacteria can attack the cells in one of the body’s
tissues. Ex. Tuberculosis (TB) – caused by bacteria
that invade the lungs and use the tissues for nutrients.
2. Bacteria can make poisons called toxins that can be
carried in the blood to other parts of the body.
ex. Food poisoning – toxins released by a type of
bacteria.
18.1 Studying Viruses and Prokaryotes
18.1 Studying Viruses and Prokaryotes
Antibiotics are used to fight bacterial disease.
• Antibiotics may stop bacterial cell wall formation.
• Antibiotics do not work on viruses.
• Prevention is best method to fight bacterial disease.
18.1 Studying Viruses and Prokaryotes
Bacteria can evolve resistance to antibiotics.
• Bacteria are gaining resistance to antibiotics.
A bacterium carries
– overuse
genes for antibiotic
resistance on a plasmid.
– underuse
– misuse
A copy of the plasmid is
through
• Antibiotics must be transferred
conjugation.
used properly.
Resistance is quickly
spread through many
bacteria.