Transcript Viruses and bacteria




The word bacteria is so familiar that we will use
it as a common term to describe prokaryotes.
Prokaryotes come in many sizes and shapes,
they are unicellular organisms that lack a
nucleus.
Classified into two kingdoms….Eubacteria and
Archaebacteria



The larger of the two kingdoms
Live almost everywhere…water, land, and
within the human body.
Very diverse with many different lifestyles.




They contain a cell
wall which is made of
a carbohydrate called
peptidoglycan.
Also have a cell
membrane and
cytoplasm.
Some include flagella
for movement.
The pili are involved
in cell-to-cell contact.




They are alike to eubacteria in the fact that they
are small, lack nuclei, and have a cell wall but
chemically they are quite different.
They LACK the carbohydrate called
peptidoglycan in their cell walls.
The DNA sequences of key archaebacterial
genes are more like those of eukaryotes than
those of eubacteria.
Scientists reason that archaebacteria my be the
ancestors of eukaryotes.




They live in harsh
environments.
Some produce methane
gas.
They can live in oxygen
free environments.
Some live in thick mud,
intestines of animals,
hot springs, or
extremely salty
environments.

Prokaryotes are identified by characteristics
such as




Shape
Chemical Nature of Cell Walls
Movement
How they obtain energy.

Rod-Shaped prokaryotes are called bacilli

Spherical prokaryotes are called cocci

Spiral shaped prokaryotes are called Spirilla



Some move some do
NOT
Some have flagella
while others lash,
snake, or spiral
forward.
Still others glide
slowly along a layer
of slime like material
they secrete.


Bacteria will vary depending on
their source of energy and whether
or not they use oxygen for cellular
respiration.
Heterotrophs or Autotrophs


Some heterotrophic prokaryotes must take in organic
molecules for both energy and a supply of carbon they
are called chemoheterotrophs. Most animals (humans
too) are chemoheterotrophs.
A smaller group of heterotrophs prokaryotes are called
photoheterotrophs. These organisms are
photosynthetic BUT they also need to take in organic
compounds such a carbon sources.



Some groups of autotrophs called photoautotrophs use
light energy to convert carbon dioxide and water to
carbon compounds and oxygen in a process similar to
that of green plants.
These live in an environment where light is abundant
like near the surfaces of lakes, streams and oceans.
Ex: cyanobacteria




Other prokaryotes make organic carbon molecules
from carbon dioxide but do NOT require light. They
are called chemoautotrophs.
Instead, they use energy directly from chemical
reactions involving ammonia, hydrogen sulfide,
nitrites, sulfur, or iron.
Some chemoautotrophs live in deep in the darkness of
the ocean. They obtain energy from hydrogen sulfide
gas that flows from hydrothermal vents on the ocean
floor.


Bacteria need a constant supply of energy. This energy can
be released by the process of cellular respiration and
fermentation or BOTH.
Obligate Aerobes- require constant source of oxygen


Obligate anaerobes- must live in the absence of oxygen.


Ex; Mycobacterium tuberculosis…cause tuberculosis
Ex: Clostridium botulinum found in soil…it can grow in canned
food because it does not require oxygen
Facultative anaerobes- can survive with or without oxygen.
Because of this they can live just about anywhere.

Ex: E.coli—lives anaerobically in the large intestines and
aerobically in sewage or contaminated water.



When a bacterium has
grown so that it has
nearly doubled in size,
replicates its DNA and
divides in half,
producing 2 daughter
cells.
This is known as binary
fission.
Does not exchange
genetic info….asexual
reproduction.


During Conjugation, a
hollow bridge forms
between two bacterial
cells, and genes move
from one cell to the
other.
This transfer of
genetic information
increases genetic
diversity in
populations of
bacteria.




During harsh conditions
some bacteria have
developed a structure
called a spore.
This spore will enclose a
portion of the bacteria’s
DNA and cytoplasm.
It can remain dormant
for months or years
until more favorable
conditions.
This allows the bacteria
to survive.

Ex: Bacillus
anthracis…which
causes the disease
anthrax is one such
bacteria.



Viruses can be very
difficult to
understand.
A biologist, Wendell
Stanley in 1935
inferred that viruses
were NOT alive.
Viruses are particles
of nucleic acid,
protein, and in some
cases lipids.


Viruses differ widely
in terms of size and
structure
They all enter living
cells and once inside
use the machinery of
the infected cell to
produce more viruses.


Most viruses are so
small then cannot
be seen without an
electron
microscope.
A typical viruses is
composed of a core
of DNA or RNA
surrounded by a
protein coat called
a capsid.

The simplest viruses
contain only a few
genes whereas the
most complex may
have more than a
hundred genes.




The capsid includes proteins that enable a virus
to enter a host cell.
Once inside the, the viral genes are expressed.
Sometimes the genetic program causes the host
cell to make copies of the virus, and in the
process the host cell is destroyed.
Because the virus must bind to certain proteins
on a cell surface and then use a host’s genetic
system MOST viruses are highly specific to the
cells they infect.



Plant viruses infect plant cells
Animal viruses usually only infect certain
related species
Viruses that infect only bacteria are called
bacteriophage.
Bacteriophage
Tobacco Mosaic
Virus
Influenza
Virus


Once the virus is inside the host cell two
different process may occur.
Lytic Infection or Lysogenic Infection




Lytic Infection- a virus enters a cell , make a copy
of itself, and causes the cell to burst.
Lysogenic Infection-, a virus integrates its DNA
into the DNA of the host cell, and the viral genetic
information replicates along with the host cells
DNA
The viral DNA that is embedded in the host’s
DNA is called a prophage. It may remain in the
host cell for many generations before becoming
active.
Assignment- Draw, color, and label Figure 19.10 on
page 481




Some viruses contain RNA as their genetic
information are called Retroviruses.
When they infect a cell they must use their
RNA to create a DNA copy, which can then be
inserted into a host cell.
They get their name “retro” meaning
backwards because usually we go from DNA
to RNA and in this cause it goes
backwards…RNA to DNA
The virus that causes acquired immune
deficiency syndrome (AIDS) is a retrovirus.



Bacteria and viruses are
everywhere in nature.
Its pathogens--disease
causing agents that get all
the attention.
Bacteria can cause disease
in one of two ways.

1. The bacteria damage
the cells and tissues of the
infected organisms
directly by breaking down
the cells for food.


Ex: Tuberculosis
2. Other bacteria release
toxins that travel
throughout he body
interfering with the
normal activity of the
host.

Ex: Strep throat and
diphtheria


Some bacterial
diseases caused by
pathogenic bacteria
include Lyme disease,
tetanus, strep throat
and tooth decay.
Many such disease
can be prevented by
stimulating the body’s
immune system with
a vaccine.


A vaccine is a
preparation of
weakened or killed
pathogens.
When injected into the
body, a vaccine
sometimes prompts
the body to produce
immunity to the
disease.




Antibiotics can also be used once the bacterial
infection does occur.
Antibiotics are compounds that block the
growth and reproduction of bacteria.
Penicillin and tetracycline are antibiotics.
The dramatic increase in human life expectancy
during the past two centuries can be attributed
to the better understanding on how to prevent
and cure bacterial infections.

Although most
bacteria are harmless
and many are
beneficial, the risks of
bacterial infection are
great enough to
warrant efforts to
control bacterial
growth.

There are various
methods used to
control bacterial
growth, including
sterilization,
disinfectants, and
food processing.


Like bacteria, viruses
produce disease by
disrupting the body’s
normal equilibrium.
The virus will attack
and destroy certain cells
in the body, causing
symptoms.



Unlock bacterial
diseases, viral diseases
cannot be treated with
antibiotics.
The best way to protect
against viruses is
prevention often by the
use of vaccines.
The symptoms of the
infections can often be
treated but NOT the
viruses.