Transcript Bacteria and viruses

BACTERIA AND VIRUSES
Biology 112
PROKARYOTES
Smallest and most common microorganisms
Unicellular organisms that lack a nucleus
They can be divided into two separate groups
Eubacteria
Archaebacteria
EUBACTERIA
 Live almost everywhere
 Usually surrounded by a cell wall that protects it
from injury as well as determines its shape
 Cell wall contains peptidoglycan, a carbohydrate
 Cell membrane inside the cell wall that surrounds
the cytoplasm
 Some have a second membrane which further
protects it from damage
ARCHAEBACTERIA
 Have cell walls, lack nuclei and lack the
peptidoglycan that is present in eubacteria
 There are different lipids existing in their cell
membranes
 The DNA sequencing is more similar to eukaryotes
than prokaryotes
 May be the ancestors of eukaryotes
 Most live in harsh environments, including mud,
digestive tracts, volcanoes
IDENTIFYING PROKARYOTES
 Shape
 Rod-shaped (bacilli), spherical (cocci),
spiral/corkscrew (spirilla)
 Composition of Cell Walls
 Thick peptidoglycan walls (gram positive) or thinner
walls with a second outer lipid layer (gram negative)
 Movement
 Some do not move at all, others have flagella, which
are whiplike structures while others still lash, snake,
spiral and glide
FOURTH IDENTIFYING CHARACTERISTIC
OF PROKARYOTES (OBTAINING ENERGY)
Heterotrophs (ex. E coli)
Autotrophs (ex.
Cyanobacteria)
HOW PROKARYOTES OBTAIN ENERGY HETEROTROPHS
Heterotrophic Prokaryotes
Eat other organisms for energy as well as a
supply of carbon
Called chemoheterotrophs
Others are autotrophs to obtain their energy
but also eat other organisms for their
necessity for carbon
Called photoheterotrophs
HOW PROKARYOTES OBTAIN ENERGY AUTOTROPHS
 Use light energy to convert carbon dioxide and water
to carbon compounds and oxygen
 Found where light is available
 Photoautotrophs
 Make organic carbon molecules from carbon dioxide
but do not require light
 Use energy from chemical reactions involving
ammonia, hydrogen sulfide, nitrites, sulfur or iron
 Present in harsh environments
 Chemoautotrophs
HOW PROKARYOTES RELEASE THEIR
ENERGY
 They undergo cellular respiration, fermentation or
both
 Those that require a constant supply of oxygen are
called obligate aerobes
 Those that do not require it (or may even be killed by
the presence of oxygen) are called obligate
anaerobes
 Those that can survive with or without oxygen are
called facultative anaerobes
 Do not require it but are not harmed by it either
 As a result, they can survive almost anywhere
GROWTH AND REPRODUCTION
 How fast they grow and reproduce depends mostly on
availability of food and the production/elimination of waste
products
 When a prokaryote has doubled in its size, it may divide in
half through a process called binary fission (daughter cells
are identical to single parent cell – asexual reproduction)
 Conjugation occurs when a bridge forms between two cells
and genetic material can be passed between the two
 Spore formation, called endospores, may form within a
prokaryote
 A thick wall forms around the DNA and a portion of the
cytoplasm
 Spore may remain dormant until more favorable conditions
occur
IMPORTANCE OF BACTERIA
Critical for maintaining the living world
Some are producers as well as decomposers
Others have uses in human survival
Decomposers
Bacteria recycles nutrients which maintains
balance in the environment
Without them, sewage systems would not be
able to eliminate all its waste and disease
would spread
IMPORTANCE OF BACTERIA
Nitrogen fixers
Plants need nitrogen to make amino acids
(building blocks of protein)
Nitrogen (N 2) must be changed to ammonia
(NH 3) or other nitrogen compounds (nitrates)
before it can be used by living things
This process is known as nitrogen fixation
IMPORTANCE OF BACTERIA – HUMAN
USES
 Human uses
 Food industry
 Lactobacillus is used for the preservation of dairy
 Industry
 Sulfate-reducing bacteria in the petroleum industry
 Waste removal
 Bacteria that converts waste into fuel
 Mining
 Bacteria that leaches copper from mines
 Synthesize drugs and chemicals for improved health
 Vaccines
VIRUSES
 Viruses are composed of parts of nucleic acid,
protein and lipids
 Reproduction only occurs by infecting living cells
 Great variety in their size and appearance
 All viruses infect cells the same way – by entering
healthy cells and once inside, use the organelles of
the infected cell to produce more viruses
 It is typically composed of DNA, RNA and a protein
coat
STRUCTURE OF A VIRUS
 Protein coat is also called a capsid
 Contains proteins that enable the virus to enter the
host cell
 Binds to receptors on a healthy cell and “tricks” the
cell into allowing it to enter
 Once inside, viral genes are exposed to the cell
 The healthy cell ‘reads’ the genetic information and
then may, as a result, get destroyed in the process
 The host cell may also make copies of the virus
VIRUSES ATTACK DIFFERENT ORGANISMS
Viruses are highly specific to the host cell it is
infecting
As a result, viruses which target plants may
not contain the proteins in their capsids to
gain entry to an animal cell
Viruses that attack bacteria are called
bacteriophages
VIRAL INFECTION
 Some viruses replicate themselves immediately once inside
the host cell and kill the cell
 Others do not replicate in such a way that destroys the host
cell immediately
 Lytic Infection
 Virus enters cell, replicates itself, and causes the cell to
burst
 Destroys the cells DNA, uses the cell to make viral proteins
and viral DNA, then releases viral particles
 Lysogenic Infection
 Incorporation of the viruses DNA with the host cell DNA and
replicates along with the host cell’s DNA
 Viral DNA is called a prophage which may lay dormant for an
indefinite amount of time