Download The World of Microbes: Viruses & Bacteria

The World of Microbes:
Viruses & Bacteria
AP Biology
Chapter 23
Microbes are…

Viruses
Bacteria

Protists


Microbiology is the study of
microbes!
Small is Relative!
1µm
Staphylococcus
Cyanobacterium
Escheria coli
Eukaryotic Cells
(10-100 µm)
Prokaryotic Cells
(0.2-10 µm)
Viruses
(0.05-0.2 µm)
Viruses
Viruses

Viruses
• DNA or RNA surrounded by a protein coat
• Parasitic - require a host cell (like cells of your
body) to replicate
• Infect all kinds of organisms:
 Bacteria
 Plant cells
 Animal cells
• Some viruses only affect certain parts of their
hosts

ex. Rabies affects nervous system
Are Viruses Alive?

Viruses are not regarded as living
organisms; lack some attributes of life.
• Are infectious particles, incapable of
replicating independently.
• Lack cellular organization and
metabolism.
Viruses

Replication
• Viruses reproduce only inside living
cells.
• Viruses replicate by infecting
susceptible cells and using the cell
to make more viruses.
Viruses




Various illnesses:
 flu, AIDS, common cold
Some antiviral medicines
Evolve very, very, rapidly
 Makes effective treatment difficult
Each virus has a host range
 A limited number of host cells that
it can infect
Virus Shape


Viral shape is determined by the nature of
the virus’s protein coat.
Viruses such as the rabies and herpes
viruses are surrounded by an extra
envelope derived from membranes of the
host cell.
Viruses Come in Many Shapes
Herpes
Rabies
Bacteriophage
Measles
Tobacco
Mosaic
Viruses infect bacteria
Bacteriophages

Viruses called bacteriophages
• Can infect and set in motion a genetic
takeover of bacteria, such as
Escherichia coli
Bacteriophages Infect Bacteria
Bacterium
Newly forming
bacteriophages



In this electron micrograph,
bacteriophages are seen attacking a
bacterium.
They have injected their genetic material
inside, leaving their protein coats clinging
to the bacterial cell wall.
The black objects inside the bacterium are
newly forming viruses.
Viral Structure - HIV
Envelope
(lipid bilayer)
Core
Proteins
Receptor
Genetic Material
2 RNA molecules
Reverse
Protein Transcriptase
Coat
Cross section of the virus that
causes AIDS


Inside is genetic material surrounded by a
protein coat and molecules of reverse
transcriptase, an enzyme that catalyzes the
transcription of DNA from the viral RNA template
after the virus enters the host cell.
HIV is among those that also have an outer
envelope that is formed from the host cell’s
plasma membrane. Spikes made of glycoprotein
(protein and carbohydrate) project from the
envelope and help the virus attach to its host
cell.
Herpes Virus
Envelope
(lipid bilayer)
Herpes Viruses
Viral DNA in
protein coat
Protein
Coat
How Viruses Replicate: Herpes
2a. Viral envelope merges
with nuclear membrane
2b. Protein coat
disintegrates;
viral DNA
copied & enters
nucleus
nucleus
envelope
coat
DNA
DNA
mRNA
(cytoplasm)
1. Virus enters cell
by endocytosis
3. Viral DNA transcribed to mRNA,
which moves to cytoplasm
How Viruses Replicate: Herpes
envelope
coat
5. New viruses
assembled & bud
from nucleus, get
envelope from inner
nuclear membrane
nucleus
DNA
DNA
mRNA
(cytoplasm)
4. MRNA makes
proteins, which
enter nucleus
6. Newly formed
viruses leave the
cell by exocytosis
Herpes Virus

Viruses such as the herpes virus can remain
hidden in the cell for a long time without
reproducing.
• Ex. Herpes virus that causes cold sores

No symptoms appear until something causes the
virus to be active,
• such as a fever or sunburn.


As long as the virus does not reproduce, there
are no symptoms.
When the virus reproduces again, the cold sores
reappear.
Viruses




Diseases caused by viruses are hard to
treat or cure.
There are no known drugs to destroy
viruses, although some may be effective in
temporarily treating them.
The white blood cells of the Immune
System may surround a destroy a virus.
Antibodies may help destroy viruses.
• Antibodies only act on one specific kind of
virus.
Viruses

Vaccines
• Harmless substances made from weakened
or dead viruses
• Stimulate the immune system to create
defenses (antibodies) against the actual
pathogen
• Can prevent certain viral illnesses

Examples: chicken pox, flu, measles,
mumps, rubella, hepatitis
Prokaryotes:
Archaea & Bacteria
The Tree of Life

All living things
classified in three
domains:
• Bacteria
• Archaea
• Eukarya
Amazing Living Things
Microbes indispensable to life:
 Produce much of Earth’s:

Oxygen
 Decomposition
 Over half of Earth’s biomass


More bacterial cells than human cells in
your body!
Prokaryotes

Prokaryotes have:
• Circular DNA, RNA, ribosomes, cytoplasm,
plasma membrane
• Most prokaryotes have a cell wall, a capsule
(around the cell wall) and a flagellum

Prokaryotes don’t have:
• Organelles such as nucleus, chloroplasts,
mitochondria.
Generalized Prokaryote
Nucleoid DNA
Plasmid DNA
Cytosol
Flagellum
Capsule
Plasma
Membrane
Cell Wall
Prokaryotic DNA



The area that contains the genetic material
is referred to as the nucleoid.
The genes are usually in one continuous
circular loop of DNA.
There may be other small circles of DNA
outside the nulceoid called plasmids.
Bacteria/Archaea

Habitats (name a place, and they live
there!)
• They are specialists

human skin, mouth, respiratory tract, large
intestine, urogenital tract, etc.

salty Dead Sea

extreme pH

archea in deep sea vents: 90-106o C
• Aerobes and anaerobes
Some Prokaryotes Thrive in Extreme
Conditions
Cyanobacteria in Yellowstone
Hot Springs
Archaea
Unique lipid membranes, cell walls, and
rRNA
 Methanogens

• Convert CO2 to methane
• Swamps, hot springs, vent communities, cow
stomachs
Halophiles - survive concentrated salt
environment
 Thermoacidophiles - thrive in hot, acidic
environment
 Generally in EXTREME environments

Bacteria

Evolve Rapidly

Most of the time are asexual

Classified by shape, locomotion, pigments,
nutrients, colonies
Bacteria

Shape:
• Cocci - round
• Bacilli - rod
• Spirilla - spirals
Three Common Bacterial Shapes
(b)
(a)
(c)
bacillus
cocci
spirillus
The Prokaryote Flagellum
Flagella
Bacterium
Bacteria

Reproduction

Reproduction is asexual, by simple
splitting (binary fission)

Daughter cells are genetic clones of
the parent cell
Binary Fission
DNA
Bacteria - Reproduction

Binary fission:
• Very fast, up to once every 20 minutes
• One bacterium-> 1021 in 24 hours.

Conjugation: (sexual reproduction)
• Used only occasionally.
Bacteria – Sexual Reproduction

Conjugation:
• Genetic variation through pili (structures
similar to flagella) and plasmid DNA
• DNA is exchanged between bacterial
cells
• Occurs through a special large, hollow
pilus
• One bacterium acts as a donor,
transferring DNA to the recipient.
Conjugation
Donor
Recipient
Sex Pilus
Benefits of Bacteria

Symbiosis (mutualism)
• Ruminants’ digestive tracts
• Nitrogen fixing in soil, nodules on certain
legumes
• Bacteria on/in the human body: intestines and
vitamin K and B12



Biodegradation - oil
Food production - cheese, yogurt,
sauerkraut
Decomposers
Our Relationship With Bacteria
Bacterial Pathogens


Some cause disease = pathogenic
In humans:
• Strep throat
• Toxins - tetanus, botulism
• Pneumonia
• "Flesh-eating" bacteria
• Plague
• Tuberculosis
• Cholera
• Lyme disease
ANTIBIOTICS= anti bacterial!!!
The Causes of Tooth Decay
Transmission of Bacterial
Pathogens



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
Airborne
Water
Food
Direct (skin contact, blood, and other
body fluids)
Insect vectors and other hosts such
as deer tick (Lyme) or mosquito.
Germ Theory of Disease


Theory that microorganisms are the
cause of disease.
1859 – Louis Pasteur
• Credited with the idea that human
diseases were caused by bacteria and
viruses (germ theory)
• Very important discovery in the field of
medicine
• Also created vaccinations to prevent
disease
Infectious Diseases


Average age of death, in first world
countries, jumped 30+ years in last
century due to antibiotics, and enhanced
hygiene and nutrition.
Antibiotic-resistant infections on the rise in
hospitals in the U.S.
• This is due to bacterial evolution in response
to widespread use of antibiotics!