Transcript Viruses and Bacteria

Viruses
What are Viruses?
 Virus—a
nonliving particle made of a
nucleic acid (DNA or RNA) and a
protein coat called a capsid.
 Virology—study
of viruses
Living or Nonliving?
 Reasons
viruses are NOT living
organisms:
 Cannot
grow, develop, or move
(they are carried)
 Cannot
reproduce on its own
Viral Structure and Attachment
Nucleic Acid
Capsid
A Bacteriophage ( a virus that only infects bacteria)
Viral Structure and Attachment

In general, viruses are species specific
and some are cell type specific.
– Species specific viruses can help control the
spread of a viral disease (Ex. Smallpox)
because they are more readily contained than
viruses that can affect both animals and
humans (Ex. Influenza aka “The Flu”)
– The recognition and attachment process is like
two pieces of a puzzle fitting together.
Viral Replication Cycles
 1.
Lytic Cycle: when a virus uses
the host cell’s energy to make new
viruses and kills the cell in the
process.
 2.
Lysogenic Cycle: when the
virus’s nucleic acid is incorporated
into the host cell’s chromosomes.
Viral Replication Cycles
 Lytic
viruses cause disease
immediately
 Lysogenic viruses take longer to
actively cause infection and they
often reoccur:
– Ex. herpes simplex I (causes cold sores in the
mouth) and herpes simplex II (causes genital
herpes).
FYI: Lytic Cycle
Chromosome
Virus
Host
cell
1. Virus attaches to a host
cell
*ATTACHMENT*
4. New viruses bust out of
the host cell, killing the
host cell *INFECTION*
2. Virus injects its
chromosome into the
host cell
*INCORPORATION*
3. The virus chromosome
uses the host cell to make
more viruses
*REPLICATION*
FYI: Lysogenic Cycle
Virus
Chromosome
Host cell
1. Virus attaches to a host
cell
4. When the cell reproduces,
the provirus is copied as part
of the chromosome
2. Virus injects its
chromosome into the
host cell
3. The virus chromosome is placed into
the host cell’s chromosome.
Provirus: viral genetic material that is
placed into the host cell’s chromosome
Releasing Viral Particles
 Exocytosis:
the virus is packaged
in small pieces of plasma membrane
that fuse with the host cell’s plasma
membrane, releasing viruses
Sugar
Step 1
Step 2
Host Cell
Step 3
HIV



Retroviruses are the most complex RNA
viruses and they only involve RNA.
Reverse transcriptase: an enzyme that
makes DNA from the virus’s RNA
(remember a virus is incorporated into the
host cell’s DNA).
HIV is a virus that infects white blood
cell.
HIV


People may be infected, but show no
signs of the disease because the host cell
still functions normally.
Spread by direct contact
– Unprotected sex, blood transfusions, sharing
needles for drugs
**Most people with an HIV infection will
eventually get AIDS because over time,
more WBC’s become infected and die.
Other Infectious Agents
 Viroid—smallest
known particle that
can cause infections
– circular, single strands of RNA
– no capsid (protein coat)
Other Infectious Agents
 Prions—proteins
that do not have
any nucleic acids, but instead cause
other proteins to fold incorrectly.
– responsible for many animal diseases
like mad cow disease and the human
equivalent Creutzfeldt-Jakob disease.
– ex. Kuru—occurred in many tribal
places
Other Viral Diseases



Tobacco mosaic virus: first virus to be
discovered (1930).
common cold
Hepatitis family (B & C are the most
common in the US and can be sexually
transmitted)
Other Viral Diseases

Ebola: 50-89% mortality; Biosafety Level
(BSL) 4 –there are only a few found in the
major countries of the world
Prevention and Treatment



1. Interferons- proteins in the immune
system that inhibit viral replication within
other cells of the body
2. Vaccines- contain live or dead viruses
and they trick the body into thinking it’s
already infected.
3. Antiviral drugs- they are made to
destroy viruses or to prevent viral
replication.
Treatment
 Antibiotics
Generally WILL NOT
WORK ON Viruses!!!
Vaccination with Cowpox
A cartoon satirizes British physician Edward Jenner, who is
shown injecting patients with cowpox virus, resulting in
their transformation into cows. Jenner lived from 1749 to
1823. His discovery that cowpox was an effective vaccine
against smallpox was initially greeted with skepticism, but
soon accepted. The procedure dramatically reduced the
incidence of smallpox, once a major cause of death in the
18th century.
Microsoft ® Encarta ® Encyclopedia 2004. © 1993-2003 Microsoft Corporation. All rights reserved.
Kingdom Archaebacteria
and Kingdom Eubacteria
Prokaryote vs. Eukaryote
Prokaryotic Cells
Eukaryotic Cells
No nucleus
Has a nucleus
Unicellular
Unicellular or
Multicellular
No membrane bound
organelles
Membrane bound
organelles
Kingdoms
Archaebacteria and
Eubacteria
Kingdoms Protista,
Fungi, Plantae, and
Animalia
Prokaryotes
 Prokaryotes
are classified into 2
different kingdoms:
– Archaebacteria: live in extreme
environments
– Eubacteria: common bacteria that live
almost everywhere
Kingdom Archaebacteria

Live in extreme habitats that are usually
very low in oxygen
Types of Archaebacteria
 1. Methanogens—produce methane (a
gas)
–Live in marshes, lake sediment, digestive
tracts, sewage treatment plants
–Oxygen is a poison– need anaerobic
conditions
Kingdom Archaebacteria
 2.
Halophiles– like salty
environments
–Great Salt Lake, Dead Sea
–use salt to make ATP (energy)
 3.
Thermophiles– live in hot, acidic
sulfur springs and deep ocean vents
Kingdom Eubacteria
 Live
almost everywhere
 Some
are heterotrophs:
– Use organic molecules as food
– Some are parasitic
– Saphrophytes—organisms that feed on
dead organisms or organic waste
Kingdom Eubacteria

Some are photosynthetic autotrophs:
– use sunlight to carry out photosynthesis and
make their own food

Some are chemosynthetic autotrophs:
– Carry out chemosynthesis:

process of breaking down and
releasing energy of inorganic
compounds containing sulfur and
nitrogen
The Structure of Bacteria
capsule
pili
DNA (chromosome)
flagella
The Structure of Bacteria
Do not have a nucleus, but do have a cell
wall, cell membrane, cytoplasm and
ribosomes
 Some have a capsule: shell covering the
cell wall that helps to protect the cell
 Some have pili: short hairlike structures
on the surface of the cell that helps to
hold onto host cells
 Many have flagella: whiplike structure on
the surface of the cell that helps in
movement

Identifying Bacteria

1. Gram staining
 stains
give bacteria color under a microscope
– Gram staining is based upon the type of cell
wall bacteria have:
 Gram positive bacteria stain purple
 Gram negative bacteria stain pink

Importance: certain antibiotics only work on
Gram positive bacteria while others only work on
Gram negative bacteria
Identifying Bacteria
 2.
By shape:
1. Rod (Bacilli)
2. Sphere (Cocci)
3. Spiral (Spiralla)

Chains begin with the prefix strepto-

Clusters begin with the prefix staphlo-
Streptococci pyogenes: Necrotizing
Fasciitis
Facts:
- If they get under the skin,
they infect soft tissues and
they are known as the flesh
eating bacteria.
-Approx 500-1500 cases a
year in the US
Vibrio cholerae: Cholera
(a bacilli)
Facts:
-One of the most rapidly fatal
diseases known
-Found in contaminated
water…how would it have
gotten there???
-Last outbreak in the
U.S. was back in 1911,
but it’s still a problem in
less developed
countries
Treponema pallidium: Syphillis
(a spiralla)
Facts:
- A curable STD
- If untreated, can cause serious
damage to the body and deterioration
in the brain, leading to madness or
even death.
Bacterial Reproduction
Can’t reproduce by meiosis or mitosis
because they don’t have a nucleus
 So, how do they do it???
1. Binary fission: asexual reproduction
because a bacterial cell copies itself

2. Conjugation: sexual reproduction
because a bacterial cell connects to
another bacterial cell through the pilus
(plural, pili) and then transfers all or
part of its DNA to the second bacterial
cell
Factors affecting growth
Growing conditions must be right
 Obligate anaerobes– bacteria that
cannot survive in presence of oxygen

– Ex: Tetanus (Lock jaw): puncture wound
deep into skin provides oxygen-free
environment for this bacteria

Facultative anaerobes– can live with or
without oxygen
– Ex: E. coli in intestines

Obligate aerobes– bacteria that can’t
survive without oxygen.
– Ex: bacteria that causes TB
Survival
 Under
unfavorable conditions, some
bacteria form endospores
 Endospore—structure that contains
bacterium’s DNA and cytoplasm.
Covered by tough outer protective
coating.
– Resting stage—no reproduction
Survival
– When conditions improve, endospore
will germinate/reproduce
 Example:
When canning foods, we must
sterilize jars and acidify food  prevents
food poisoning with botulism
 Example:
Tetanus forms endospores. When
spore enters body through wound, will
germinate and release toxins that lead to
neurological problems.
Helpful Bacteria

Uses:
– Sewage treatment plants—break down
wastes
– Food processing—bacteria create buttermilk,
sour cream, yogurt, cheese, sauerkraut, some
pickles
– Chemicals—insecticides, clean up oil spills,
genetic engineering (making insulin)
– Nitrogen fixation—can take nitrogen gas and
put it into useful compounds