chapter 20 Flashcards
what are two microscopic, single celled organisms
bacteria and archea
what does prokarytoes mean
before a nucleus
no membrane bond organelles
who discovered prokaryotes, what is referred as?
Dutch microscopist Antonie van Leeuwenhoek
father of microbiology
what did Antonie van Leeuwenhoek study?
what did he also do?
green charophyte alga Spirogyra, Dental Plaque
made microscopes
Prokaryote Structure
Lack a membrane-bounded nucleus (DNA in nucleoid region)
Outer cell wall
Some move by means of flagella
Lack membranous organelles
May have accessory rings of DNA (plasmids)
capsule
gel-like coating outside the cell wall
made up of a polysaccharide layer
called glycocalyx.
fimbriae
hairlike bristles that allow
adhesion to surfaces
nucleoid
location of the
bacterial chromosome
conjugation pilus
elongated, hollow appendage
used to transfer DNA to other cells
flagellum
rotating filament that propels the cell
what kind of DNA do prokaryotic cells have?
have a circular DNA`
Louis Pasteur
devised an experiment that showed that a previously sterilized broth cannot become cloudy with microorganism growth unless it is exposed directly to the air where bacteria are abundant.
Disproved the theory of spontaneous generation of microbes by performing these types of experiments.
Pasteur’s Experiment
HYPOTHESIS A: Bacteria arise spontaneously in a broth
HYPOTHESIS B: Bacteria in the air contaminate a broth
Reproduction in Prokaryotes
Asexual
Prokaryotes reproduce asexually by means of binary fission.
Generation time is as short as 12 minutes
mutations in prokaryotes
are generated rapidly and passed on to offspring more quickly than eukaryotes
are Prokaryotes haploid or diploid
Mutations are immediately subjected to natural selection
Conjugation
Conjugation pilus forms between two cells
Donor cell passes DNA to recipient cell through the pilus
Transformation
Occurs when bacterium picks up free pieces of DNA from other prokaryotes
Becomes incorporated into genome
Transduction
Occurs when bacteriophages carry portions of bacterial DNA from one cell to another
Serve as vectors
most common type of prokaryote
how many
bacteria
Over 9,000 different bacteria have been named (more are being named)
how do bacteria arise
from the division of preexisting bacteria—not by spontaneous generation
what do the cell wall of the bacteria contain?
peptidoglycan
how are bacteria commonly differentiated
through a gram stain procedure
Gram-negative bacteria
have a second plasma membrane which blocks antibiotic drugs, making infections difficult to treat
three basic shapes of a bacteria
Spiral (spirilli),
Rod (bacilli), and
Round (cocci)
Bacterial Metabolism
Obligate aerobes – unable to grow in the absence of free oxygen (need oxygen)
Obligate anaerobes – unable to grow in the presence of free oxygen
Examples: Botulism, gas gangrene, and tetanus
Facultative anaerobes – able to grow in either the presence or absence of free oxygen
vectors
suitcases of holding genetic info to other places and spread
Autotrophic Bacteria
Photoautotrophs
Chemoautotrophs
Photoautotrophs
Use solar energy to reduce carbon dioxide to organic compounds
Photosynthetic
Anoxygenic – Green sulfur and some purple bacteria living in oxygen-poor conditions
Oxygenic
Chemoautotrophs
Oxidize inorganic compounds to obtain energy
Energy is used to reduce CO2 to an organic compound
Chemosynthetic
Live in environments such as deep sea vents 2.5 km below sea level
Heterotrophic Bacteria
Most prokaryotes are chemoheterotrophs that take in organic nutrients.
Aerobic saprotrophs decompose most large organic molecules to smaller molecules.
Essential components of a healthy ecosystem
Heterotrophic Bacteria may be
free-living or symbiotic (two different species live together in an intimate way)
Commensalism
One population modifies the environment in such a way that a second population benefits.
Obligate anaerobes live in our intestine because bacterium E. coli uses up oxygen.
Mutualism
Both species benefit from association.
Mutualistic bacteria live in human intestines and release vitamins K and B12 which help produce blood components.
produce blood components.
Parasitism
Parasite benefits at host expense; disease-causing bacteria are called pathogens
Many form endospores
Cyanobacteria!
(Formerly called the blue-green algae (Cyanophyta))
are Gram-negative bacteria that are photoautotrophic
Believed to be responsible for introducing oxygen into the primitive atmosphere
Cyanobacteria charcteristics
Lack visible means of locomotion
Can live in extreme environments
In association with fungi, form lichens
They possess heterocysts, cells without nuclei, where nitrogen fixation occurs.
Cyanobacterial “blooms” result from pollution in lakes and ponds
Antibiotic compounds fall into two classes
Compounds that inhibit protein biosynthesis
Compounds that inhibit cell wall biosynthesis
Compounds that inhibit protein biosynthesis
Erythromycin
Tetracycline
Compounds that inhibit cell wall biosynthesis
These affect bacterial but not animal cells
Penicillin
Ampicillin
Fluroquinolone
Bacterial resistance to antibiotics is increasing.
Genes conferring resistance can be transferred among bacteria by transformation, conjugation, or transduction.
Now 90% of Staphlococcus aureus are resistant to penicillin and increasingly to methicillin (MRSA).
MRSA is common in hospitals and nursing facilities.
Carl Woese and George Fox
discovered that the base sequence of their rRNA differs from bacteria.
archea Other differences
Archaea do not have peptidoglycan in their cell walls like the bacteria.
Archaea are biochemically more like eukarya than bacteria.
Archaea are now thought to be more closely related to
eukarya than to bacteria.
Many live in harsh conditions:
Anaerobic marshes
Methanogens
Produce methane from hydrogen gas and carbon dioxide
Salty lakes
Halophiles
Require high salt concentrations for growth
Hot sulfur springs
Thermoacidophiles
Reduce sulfides and survive best at temperatures above 80ºC
Plasma membranes contain unusual lipids that confer tolerance of high temperatures
Viral Structure and Classification
Each type has at least two parts (capsid and core)
Viruses are characterized by
Size and shape
10–400 nm in diameter
Type of nucleic acid core
Single stranded or double stranded? DNA or RNA?`
Capsid
outer layer composed of protein subunits
Capsid or no capsid
Some are enveloped by membrane
Others “naked”
obligate intracellular parasites`
Cannot reproduce outside a living cell
Are either active or inactive, instead of living or non-living
Hypotheses about viral origin and evolution
Proteins and nucleic acids, organic molecules in viruses, evolved and
viruses may have arisen from these two basic polymers when cells did.
Viruses may have been derived from pieces of cell genomes.
Viruses may have evolved backwards from living cells.
Viruses degenerated from living cells.
Bacteriophages
Viruses that infect bacterial cells
There are two types of bacteriophage life cycles.
lytic cycle
Viral reproduction occurs
The host cell undergoes lysis
Hundreds of virus particles are released
lysogenic cycle
Virus becomes integrated into the host genome and may reenter lytic cycle.
This is known as latency and the latent viral DNA is called a prophage.
Reproduction of Animal Viruses
Animal virus enters the host cell Uncoating releases viral DNA or RNA Budding: Viral particles released in a bud Acquires a membranous envelope
Retroviruses
(HIV, the virus that causes AIDS)
Contain reverse transcriptase
Carries out RNA cDNA reverse transcription
cDNA becomes integrated into host DNA
Replicated as host DNA replicates
HIV may remain latent for years
Viral DNA is transcribed; new viruses are produced
A flu virus has an
H (hemagglutinin) spike and an N (neuraminidase) spike
H spike
allows the virus to bind to the receptor
16 different types
N spike
attacks host plasma membranes
Allows mature viruses to exit the cell
9 different types
characteristics of spikes
Each type of spike can occur in different varieties.
Our immune system only recognizes H spikes and N spikes it has been exposed to.
Currently the H7N9 and H5N1 subtypes of flu virus are of great concern because they can potentially become pandemics (global outbreaks).
Emerging viruses are new or previously uncommon illnesses.
Examples are AIDS, West Nile encephalitis, hantavirus pulmonary syndrome (HPS), severe acute respiratory syndrome (SARS), Ebola, hemorrhagic fever, and avian influenza
Several types of events can cause emergence of viruses
A virus may extend its range.
Example: West Nile was transported to US and took hold in birds and mosquitoes
A genetic mutation may occur.
Example: Influenza strains H5N1, H1N1, and H7N9 were created through mutation of flu viruses which only infected animals
It is necessary to obtain flu vaccine each year due to the rapidly mutating flu virus
Viruses are best known for
causing infectious diseases in plants and animals.
Herpes, HIV, cancer
Viruses lack metabolism; thus, antibiotics have no effect
Viroids
Naked strands of RNA
Many crop diseases
Prions
Protein molecules with contagious tertiary structure
TSEs are neurodegenerative diseases which destroy nerve tissue in the brain
They are untreatable and fatal
Some human and other animal diseases: Mad cow disease
Some practices, including eating brains of cattle, transmitted the cattle disease (BSE or bovine spongiform encephalopathy) to humans.
nitrogen fixing
convert gaseous nitrogen into usable forms
who could have brought oxygen to the earth first?
bacteria (cynobacteria)
size and color of cynobacteria pigments
many different colors and large in size
mutualistic relationships for bacteria
fungi to form lichens
symbiotic relationships`
Intimate relationships between two different species are called
commensalistic relationships
that exist in the intestines of humans.
