Transcript Viruses and Bacteria

 Viruses
are non-living particles that are
composed of a protein coat called a
capsid and a nuclei acid core, either
DNA or RNA.

Viruses are all parasites and must live
inside a host cell to replicate themselves.
 Before
a virus can enter it’s host cell it
must recognize and attach to receptors
on the plasma membrane of the host cell.
 Viruses
have specifically shaped
attachment proteins that will match
receptors on only specific cells.
 Example:
cells.
Hepatits viruses attach to liver
 Shapes
of Viruses
 Virus
uses the host cell’s energy, raw
materials and enzymes to make new
viruses.
A
typical lytic cycle takes about 30
minutes to produce about 200 new
viruses.
 The
lytic cycle destroys the host cell.
 In
the lysogenic cyle, the viral nucleic acid
becomes part of the host DNA; it is
integrated into the host chromosome
 While
it is integrated, the viral DNA is called
a provirus.
 It
does not affect the host cell, but is copied
every time the host cell reproduces.
 Eventually, the
provirus emerges from the
host DNA and becomes active.
 Lytic
viruses:
 Lysogenic

common cold
• Hepatitis

influenzae
• HIV

measles
• Herpes
viruses:
Retroviruses are lysogenic viruses that have
RNA as their genetic material.
In order to integrate into host DNA, must be
able to copy their RNA into DNA - reverse
transcription.
Retroviruses carry an enzyme called “reverse
transcriptase” that enables them to convert
RNA into DNA.
 HIV
is a retrovirus that infects a group of
disease fighting white blood cells called
Helper – Tcells.
When HIV emerges from it’s provirus stage,
it destroys cells of the immune system and
makes the infected person susceptible to
many infections and diseases.
This is when the person develops AIDS.

Examples: HPV is associated with
cervical cancer.
 Prions
are infectious particles that are
composed of misfolded proteins.
 They
are infectious .
 Cause “mad
cow disease” in cows and
“Creuzfeldt-Jakob disease” in humans.
 Viroids
are small circular RNA particles
and found only in plants.
 They
have been found to cause infectious
disease in plants.
 Since
viruses cannot replicate without a
host cell, viruses probably originated
from their host cells.
 Prokaryotes
are unicellular organisms
that have no nucleus or membrane bound
organelles.
 Prokaryotes
are divided into two
kingdoms:
• Archaebacteria – these are probably the
descendents of the first bacteria that became the
ancestors or eukaryotic cells.
• Eubacteria - the modern bacteria
 Archaebacteria
live
in extreme conditions
in places that have no
free oxygen.
• Thermophiles - live in
high temperature, may
be found in boiling mud
pots. (Yellowstone
National Park)

Halophiles - saltloving bacteria can
exist in very high salt
concentrations.
These are found in
the Great Salt Lake in
Utah and the Dead
Sea in the Middle
East.
 Methanogens
live in
oxygen free
environments and
produce methane
gas.
 They are found in
marshes, lake
sediments, under the
arctic ice and in the
digestive tracts of
some grazing
animals.
 Types
of Eubacteria based on how they
get food.
• Heterotrophic: these are most bacteria; they are
everywhere and use organic molecules as food.
• Photosynthetic autotrophs: these bacteria make
their own food using light (sun) as their energy
source. The cyanobacteria are the most
common.
• Chemosynthetic autotrophs: these bacteria
breakdown and release the energy stored in
inorganic molecules to produce their own food.




Capsule
• Gelatin coating around some bacteria that protect them
from immune system.
Pilus
• Hair-like structure on the surface of some bacteria that
allow them to stick to each other – can exchange genetic
information through pili
Flagella
• Whiplike structure that some bacteria use to move
Plasmid
• Small circular piece of DNA in addition to the chromosome that
carries a few genes, often antibiotic resistance
 Bacteria
shapes:
have three
• Cocci which are
spherical shaped
• Bacilli which are rod
shaped
• Spirilli which are
spiral shaped
 Diplo
- means in
pairs
 Strepto
- means in
chains
 Staphylo
clusters
- means in
 Bacteria
may stain gram positive (purple) or
gram negative (pink) based on their cell walls.
A
gram positive bacteria has one layer of a
sugar protein complex in its cell wall which
reacts with the purple stain and holds it.
A
gram negative bacteria has a lipid type layer
over the inner sugar protein cell wall that
prevents the purple stain from reacting. It is
counterstained with a pink stain so that they
can be visualized.
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Put bacteria on slide and heat fix the
bacteria.
Flood slide with crystal violet for 1 minute.
Wash with water.
Flood slide with iodine for 1 minute.
Wash with water.
Decolorize for 20 seconds.
Wash with water.
Flood slide with safranin (pink) for 30
seconds.
Wash with water.
Pat dry and observe under microscope.
E. coli is a gram negative bacilli
 Staphylococcus (Staph) is a gram positive
cocci

 Bacteria
reproduce
asexually by a
process called:
Binary Fission
• The bacterial cell grows
larger
• Copies the chromosome
• Divides the cytoplasm
with each cell getting a
copy of the chromosome
• Two identical cells are
produced

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

During conjugation, one
bacteria transfers all or
part of its DNA to another
bacteria.
This occurs when the
bacteria form a bridge
connecting them call a
sex pilus.
Conjugation results in
new combinations of
genes and provides
variations.
Antibiotic resistance is
transferred through
conjugation.
 Bacteria
break down food for energy
either using oxygen (respiration) or
without oxygen (fermentation)
 Bacteria
that can only live in oxygen are
called obligate aerobes.
 Bacteria that die in the presence of
oxygen are called obligate anaerobes.
 Bacteria that can live in either condition
are called facultative anaerobes.




An endospore is a tiny
structure that contains a
bacteria’s DNA and a
small amount of
cytoplasm surrounded
by a tough outer
covering.
They are produced by
some bacteria when
environmental conditions
are unfavorable.
They can remain in this
condition until favorable
conditions return.
This is not reproduction
because it is the same
bacteria.
 Nitogen
Fixation: Bacteria are the only
organisms that can use atmospheric
nitrogen and change it into a useable
form for plants and animals.
• All living organisms require nitrogen to make
proteins and nucleic acids.
 Recycling
of Nutrient: Bacteria and fungi
are the main decomposers returning
nutrients back to the environment.
 Foods and Medicines
• Bacteria are used in the production of cheeses, yogurt,
pickles, and saurkraut.
• Some bacteria are used to produce antibiotics.
 Bacteria cause disease
• Some bacteria produce toxins (poisons) that cause
disease.
 Examples: cholera, botulism
• Other bacterial diseases
 Strep throat - Streptococcus pyogenes
 Tuberculosis - Mycobacterium tuberculosis
 Pneumonia - Streptococcus pneumoniae
 Gonorrhoea - Neisseria gonorrhoeae
 Tetanus - Clostridium tetani