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Ch. 27 Bacteria and Archaea (Concept 27.1 Structural & Functional…
Ch. 27 Bacteria and Archaea
Concept 27.1 Structural & Functional Adaptations Contribute to Prokaryotic Success
Cell-Surface Structures
Cell Wall
functions:
maintaining cell shape, protects the cell, and prevents it from bursting in a hypotonic environment (see Figure 7.12)
in a hypertonic solution, most prokaryotes LOSE water and SHRINK away from their wall (plasmolyze)
Peptidoglycan
a polymer composed of modified sugars cross-linked by short polypeptides.
Archaeal cell walls: variety of polysaccharides & proteins; lack peptidoglycan.
Gram stain
Gram-Positive
simple walls composed of a think layer of peptidoglycan
some also have virulent strains that are resistance to one or more antibiotics.
Gram-Negative
contain less peptidoglycan
structurally more complex
outer membrane contains lipopolysaccharides (carbs bonded to lipids); helps protect it from the body's defenses
lipid portions in the walls are toxic, causing fever or shock;
more resistant than gram-positive species to antibiotics bc the outer membrane impedes entry of the drugs.
1) crystal violet and iodine
2) rinsed in alcohol
3) stained with a red dye such as safranin that enters the cell and binds to its DNA.
very important tool in medicine to determine whether a patient's infection is due to gram-negative/gram-postive infection.
capsule
defined as:
the sticky layer of polysaccharide or protein on cell walls of prokaryotes
also a
slime layer
, if not well organized
both sticky layers enable prokaryotes to adhere to their substrate or to other individuals in a colony.
some protect against dehydration, shield pathogenic prokaryotes from attacks by their host's immune system
endospores
bacteria develop these resistant cells when they lack water or essential nutrients
original cells then lyses, releasing the endospore
very durable
can survive in boiling water; killing requires 121 C
self improve themselves when they remain dormant but viable & environment improves
Fimbriae
hairlike appendages that help some prokaryotes stick to their substrate
Ex: the bacterium that causes gonorrhea, uses fimbriae to fasten itself to the mucous membranes of its host.
usually shorter and more numerous than pili
Pili
appendages that pull two cells together prior to DNA transfer from one cell to another.
referred to as
sex pili
Motility
taxis
a directed movement toward or away from a stimulus
ex: prokaryotes that exhibit
chemotaxis
change their mvmd pattern in response to chemicals. They may move
toward
(+) nutrients or
away from
a toxic substance (-).
Flagella
most common structure that allows prokaryotes to move
bacteria and archaea are similar in size and rotational mechanism, but composed differently and unrelated proteins.
described as analogous
Evolutionary Origins of Bacterial Flagella
3 main parts
the motor
two proteins in the motor are homologous to proteins that function in ion transport.
hook
filament
only half of the flagellum's protein components appear to be necessary for it to function; the others are inessential or not encoded in the genomes of some species.
exaptation
the process in which structures originally adapted for one function taking on new functions through descent with modification.
Internal Organization and DNA
Prokaryotes have circular chromosomes and eukaryotes have linear chromosomes
the chromosome of prokaryotes is associated with many fewer proteins than are the chromosomes of eukaryotes
prokaryotes lack a nucleus; their chromosome is located in the
nucleoid
- not enclosed by a membrane
plasmids
are smaller rings of independently replicating DNA molecules, carrying a few genes.
Reproduction
binary fission
prokaryotic cell divides into 2 cells, then divides into 4, 8, 16 and so on.
prokaryotes divide every 1-3 hours; some in just 20 minutes
Rapid population growth emphasize on 3 key features:
small, binary fission reproduction, short generation times
.
Concept 27.3 Diverse nutritional and metabolic adaptations have evolved in prokaryotics
The Role of Oxygen in Metabolism
Obligate Aerobes
must use O2 for cellular respiration; without it they cannot grow.
Obligates Anaerobes
poisoned by O2
live exclusively by fermentation;
some others extract chemical energy by
anaerobic respiration
: in which substances other than O2, like NO3- or SO42-, accept electrons at the "downhill" end of electron transport chains.
Facultative anaerobes
use O2 if present, but can also carry out fermentation or anaerobic respiration in an anaerobic environment.
Nitrogen Metabolism
Nitrogen Fixation
For Example, some cyanobacteria and methanogens convert atmospheric nitrogen (N2) to ammonia (NH3).
The cells can incorporate this "fixed" nitrogen into amino acids and other organic molecules.
Ex: nitrogen-fixing prokaryotes can increase the nitrogen available to plants, which cannot use atmospheric nitrogen but N compounds that prokaryotes produce from ammonia
Table 27.1 Major Nutritional Modes
Autotroph
Mode:
Photoautotroph
Carbon source
CO2, HCO3-, or related compound
Types of Organisms
Photosynthetic prokaryotes (ex:cyanobacteria); plants; certain protists (ex: algae)
Energy Source
Light
Mode:
Chemoautotroph
Energy Source
Inorganic Chemicals (such as H2S, NH3, or Fe3+
Carbon Source
CO2, HCO3-, or related compound
Types of Organisms
Unique to certain prokaryotes (for example,
Sulfolobus
)
Heterotroph
Photoheterotroph
Light Source
Organic Compounds
Type of Organism
Unique to certain aquatic and salt-loving prokaryotes (Ex:
Rhodobacter Chloroflexus
Energy Source
Light
Chemoheterotroph
Light Source
Organic Compounds
Types of Organisms
Many prokaryotes (ex:
Clostridium
) and protists; fungi; animals; some plants
Energy Source
Organic Compounds
Metabolic Cooperation
Heterocysts
carry out only nitrogen fixation.
surrounded by a thickened wall that restricts entry of O2 produced by neighboring photosynthetic cells.
Intercellular connections allow heterocysts to transport fixed nitrogen to neighboring cells and to receive carbohydrates.
Biofilms
surface-coating colonies that allow metabolic cooperation between different prokaryotic species.
Cells in a biofilm secrete signaling molecules that recruit nearby cells, causing the colonies to grow.
Channels in the biofilm allow nutrients to reach cells in the interior and expel wastes.
Concept 27.2 Rapid reproduction, mutation, and genetic recombination promote diversity in prokaryotes
Rapid Reproduction & Mutation
After repeated rounds of division, most of the offspring cells are genetically identical to the original parent cell.
Ex: bacterium
E. Coli
reproduces by binary fission in a human intestine, one of its natural environments.
if any errors occur during DNA replication, some offspring may differ genetically.
prokaryotes are not "primitive" or "inferior" in an evolutionary sense; causinf to reproduce more rapidly than eukaryotes.
Genetic Recombination
Transformation and Transduction
Transformation
the genotype and possibly phenotype of a prokaryotic cell are altered by the uptake of foreign DNA from its surroundings.
Ex: a harmless strain of Strep pneumonia can transform into pneumonia causing cells if the cells are exposed to DNA from a pathogenic strain.
this occurs when a nonpathogenic cell takes up a piece of DNA carrying the allele for pathogenocity and replaces its own allele with a foreign allele; exchange of homologous DNA segments
Cell = Recombination; its chromosome contains DNA derived from two different cells.
Transduction
Conjugation & Plasmids
Conjugation
DNA is transferred between two prokaryotic cells (of the same species) that are temporarily joined.
In bacteria, the DNA transfer is always one-way: One cell donates the DNA and the other receives it.
1) a pilus from the donor cell attaches to the recipient
2) Pilus retracts, pulling the two cells together, like a grappling book.
3) The formation of a temporary structure b/w the two cells form "a mating bridge" through which the donor transfers DNA to the recipient.
the ability to form pili and donate DNA during conjugation results from the presence of the
F factor
F is for fertility.
Plasmids
The F Factor as a Plasmid
known as
F plasmid
Cells containing the F plasmid designated F+ cells, function as DNA donors during conjugation
Cells lacking F factor, designated F-, function as DNA recipients during conjugation.
The F+ cell can convert F- cell to F+ if a copy of the entire F plasmid is transferred.
The F Factor in the Chromosome
Chromosomal genes can be transferred during conjugation when the donor cells F factor is integrated into the chromosome.
A cell with the F factor built into its chromosome is called
Hfr cell
(high frequency of recombination)
Hfr cell functions as a donor during conjugation with an F- cell
Hfr and F- chromosomes align allowing segments of their DNA to be exchanged.
R Plasmids and Antibiotic Resistance
R plasmids
: are plasmids that carry resistance genes
"resistance genes" code for enzymes that specifically destroy or otherwise hinder the effectiveness of certain antibiotics, such as tetracycline or ampicillin.
Exposing a bacterial population to a specific antibiotic will kill anitbiotic- sensitive bacteria, but not the ones containing R plasmids with genes that counter the antibiotic.
R plasmids carry genes for resistance; causing a huge problem for anitbiotics to fight off a bacterial infection.
The problem is compounded by the fact that many R plasmids, like F, have genes that encode pili & enable DNA transfer from one bacterial cell to another by conjugation.
Concept 27.5 Prokaryotes play crucial roles in the biosphere*
Chemical Recycling
Cyanobacteria & other prokaryotes use CO2 to make sugars, that'll be passed up through food chains.
prokaryotes can also decrease the availability of key nutrients
prokaryotes also convert some molecules to forms that can be taken up by other organisms
Ex: some chemoheterotrophic prokaryotes function as
decomposers
, breaking down dead organisms and waste products, thus unlocking supplies of carbon, nitrogen & other elements.
Ecological Interactions
symbiosis
: ecological relationship in which two species live in close contact w/ each other.
host
:larger organism
symbiont
: smaller organism
mutualism
ecological interaction b/w two species in which both benefit
commensalism
one species benefits while the other is not harmed or helped in any significant way
Ex: more than 150 bacterial specie live on the outer surface of your body
Parasitism
ecological relationship in which a
parasite
eats the cells contents, tissues, or body fluids of a host.
parasites that cause disease are known as
pathogens
, which many are prokaryotic.
Concept 27.4 Prokaryotes have radiated into a diverse set of lineages
An Overview of Prokaryotic Diversity
horizontal gene transfer
distant related species
mosaic of genes imported from other species
It is still unclear how prokaryotes have evolved into bacteria and archaea.
Bacteria
every major mode of nutrition and metabolism is represented among bacteria
Proteobacteria: Alpha, Beta, Gamma, Delta, Epsilon Proteobacteria; Chlamydias; Spirochetes; Cyanobacteria; Gram Positive Bacteria
Table 27.2 A Comparison of the Three Domains of Life
Domain
Archaea
Nuclear Envelope:
Absent
Membrane Enclosed Organelles:
Absent
Peptidoglycan in cell wall:
Absent
Membrane Lipids:
Some branched hydrocarbons
RNA polymerase:
Several Kinds
1 more item...
Eukarya
Nuclear Envelope:
Present
Membrane-Enclosed Organelles:
Present
Peptidoglycan in Cell Wall:
Absent
Membrane Lipids:
Unbranched Hydrocarbons
RNA polymerase:
Several kinds
1 more item...
Bacteria
Nuclear Envelope:
Absent
Membrane Enclosed Organelles:
Absent
Peptidoglycan in cell wall:
Present
Membrane Lipids:
Unbranched hydrocarbons
RNA polymerase:
One kind
1 more item...
Archaea
extremophiles
are lovers of extreme conditions;
Include
Extreme halophiles
EH live in highly saline environments.
Ex: Great Salt Lake, Dead Sea in Israel, Spanish Lake (beginning of chapter)
Another Ex: protein and cell wall of
Halobacterium
improve function in extremely salty environments, but will die if salinity drops below 9%.
Extreme Thermophiles
Thrive in very hot environments
Ex:
Sulfolobus
live in sulfur-rich volcanic springs at ~90'C
Sulfolobus
& other extreme thermophiles are able to survive b/c their structure & biochemical adaptations make their DNA & proteins stable at high temperatures.
clade Crenarchaeota and Euryarchaeota
Methanogens
archaea that release methane as a by-product of their unique way of obtaining energy.
use CO2 to oxidize H2 gas, a process that produces both energy and methane waste.
"marsh gas" is methane released by methanogens
decomposers in sewage treatment facilities
clade Euryarchaeota
Prokaryotes vs. Eukaryotes
Comparison
both contain flagella
cell wall
DNA
Ribosomes
Contrast
Cell Walls in eukaryotes are made of cellulose or chitin (in plant or fungi)
Bacteria Cell Wall: Peptidoglycan
Flagella in prokaryotes are 1/10 the width & not covered by an extension of plasma membrane
Flagella also differ in their molecular composition and their mechanism of propulsion.
Genome of a prokaryote is structurally different from a eukaryotic genome and in most case has less DNA.
prokaryotes lack a nucleus
Concept 27.6 Prokaryotes have both beneficial and harmful impacts on humans
Pathogenic Bacteria
bacteria causes half of all human diseases
Ex: More than 1 million people die each year of lung disease tuberculosis, caused by Mycobacterium tuberculosis; 2 million from diarrheal disease caused by various bacteria.
Lyme Disease carried by fleas and ticks
Endotoxins
: lipopolysaccharide components of the outer membrane of gram-negative bacteria.
released only when bacteria die and their cell walls break down
Salmonella typhi
derive from endotoxins, cause typhoid fever
exotoxins
: proteins secreted by certain bacteria or other organisms.
Ex: Cholera is caused by an exotoxin secreted by the proteobacterium
Vibrio cholerae
Clostridium botulinum
C. difficile
Prokaryotes in Research and Technology
CRISPRs
genomes of many prokaryotes contain short DNA repeats, interact with proteins know as Cas proteins.
CRISPR-Cas9 System
has opened lines of research on HIV.
Bacteria today is being used to reduce our use on petroleum; also engineering bacteria that can produce ethanol from various forms of biomass.
bioremediation
: the use of organisms to remove pollutants from soil, air or water.
Ex: decomposition of organic matter in sewage; archaea and anaerobic bacteria can fertilize matter after chemical sterilization
usefulness of prokaryotes largely derives from their diverse forms of
nutrition and metabolism
Mutualistic Bacteria
human well being depend on mutualistic bacteria
Ex: our intestine are home to 500-1,000 species of bacteria, outnumbering human body cells in the body by a factor of 10.
Digest food that our own intestines cannot break down.
Bacteroides thetaiotaomicron
synthesizes carbs, vitamins, and other nutrients that we need.
bacterium activate human genes that build the network of intestinal blood vessels necessary to absorb nutrient molecules
