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Chapter 27: Bacteria and Archaea (Concept 27.1: Structural and functional…
Chapter 27: Bacteria and Archaea
Concept 27.1
: Structural and functional adaptations contribute to prokaryotic success
Motility
taxis
: directed movement toward or away from a stimulus
chemotaxis
: exhibited to change movement pattern in response to chemicals
positive chemotaxi: toward nutrients or oxygen
negative chemotaxis: away from toxic substance
flagellum: scattered all over or one one or both ends
Internal Organization and DNA
lack complex compartmentalization
chromosomes - circular, fewer proteins, located in nucleoid
nucleoid: region of cytoplasm not enclosed in membrane
plasmids: smaller rings of independently replicating DNA molecules, carry only a few genes each
Cell-Surface Structures
cell wall: maintain cell shape, protect cell, prevents from bursting in hypotonic environment
in a hypertonic environment, prokaryotes shrink away from cell wall(plasmolyze), inhibits cell reproduction
salt can preserve food, causes food-spoiling bacteria to lose water, preventing rapid multiplication
bacterial cell walls contain
peptidoglycan
- polymer of modified sugars cross-linked by short polypeptides
eukaryotic cell walls contain cellulose/chitin
pepti. molecular fabric, encloses entire bacterium, anchors other molecules extended on surface
archaeal cell walls lack pepti., polysaccharides and proteins
gram stain: show differences in cell wall composition
gram-negative
: less pepti., more complex, outer membrane contains lipopolysaccharides
gram-positive
: simple cell walls, thick layer of peptidoglycan
stained crystal violet, iodine, rinsed in alcohol, stained red dye, safranin, enters cell and binds to DNA
fimbriae
: hairlike appendages, stick to substrate or another
pili:/pilus longer, less numerous, appendages
sex pilus: pull two cells together for DNA transfer
endospores
: resistant cells, developed when lacks water or essential nutrients
formed when og. cells copies its chromosome & surrounds copy with multilayered structure
water removed from endospore & metabolism halts, og. cell lyses, releases endospore
capsule
: sticky layer of polysaccharide or protein, dense, well-defined
slime layer - not as well-organized
both types enable prokary. to adhere to substrates or to other prokarys., protect against dehydration, shield pathogenic prokarys. from host's immune system
Reproduction
binary fission
: single prokaryotic cell divides in 2, then 4, then 8, 16, and on, divide every 1-3 hours,
their potential for rapid population growth shows 3 key features:
they are small
produce by binary fission
often have short generation times
Concept 27.2
: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes
Genetic Recombination
transformation
: genotype and phenotype of prokaryotic cell altered by uptake of foreign DNA from surroundings
transduction
: phages carry prokaryotic genes from one host to another
conjugation
: DNA is transferred between two prokaryotic cells that are temporarily joined
Transduction
3) new phage particles assemble, fragment of bacterial DNA carrying A+ allele packaged in phage capsid
4) phage carrying A+ allele from donor cell infects recipient cell with alleles A- and B-, crossing over at two sites allow donor DNA to be incorporated into recipient DNA
2) phage DNA is replicated, cell makes copies of phage proteins, host cell's DNA becomes fragmented
5) genotype of resulting recombient cell(A+B-) differs from genotypes of donor(A+B+) and recipient(A-B-)
1) phage infects bacterial cell that carries A+ and B+ alleles, bacterium is the "donor" cell
Rapid Reproduction and Mutation
variation results from combination of rapid reproduction and mutation
binary fission
Conjunction
3) DNA replication continues in donor and recipient cells, transferred plasmid strand moves farther into recipient cell
4) when DNA transfer and synthesis complete, plasmid in recipient circularizes, recipient is now a recombinant F+ cell
2) cell synthesizes new strand using unbroken stand as a template, broken strand peels off, enters F- cell, synthesis of complementary strand begins
1) cell carrying F plasmid forms mating bridge with F- cell, one strand of plasmid's DNA breaks
Concept 27.3
: Diverse nutritional and metabolic adaptations have evolved in prokaryotes
The Role of Oxygen in Metabolism
obligate anaerobes: poisoned by O2
obligate aerobes: must use O2 for cellular respiration, cannot grow without it
Nitrogen Metabolism
nitrogen fixation
: cyanobacteria and methanogens convert atmospheric nitrogen to ammonia
Table 27.1: Major Nutritional Modes
heterotroph
photoheterotroph
energy source: light
carbon source: organic compounds
types of organisms: unique to certain aquatic and salt-loving prokaryotes,
Rhodobacter, Chloroflexus
chemoheterotroph
energy source: organic compounds
carbon source: organic compounds
types of organisms: many prokaryotes,
Clostridium
, and protists; fungi; animals; some plants
autotroph
photoautotroph
energy source: light
carbon source: CO2, HCO3-, or related compound
types of organisms: photsynthetic prokaryotes, cyanobacteria; plants; certain protists, algae
chemoautotroph
energy source: inorganic chemicals
carbon source: CO2, HCO3-, or related compound
types of organisms: unique to certain prokaryotes,
Sulfolobus
Metabolic Cooperation
heterocysts: carry out only nitrogen fixation
biofilms: metabolic cooperation between different prokaryotic species often occurs, surface-coating colonies
Concept 27.4
: Prokaryotes have radiated into a diverse set of lineages
Table 27.2 A Comparison of the Three Domains of Life
RNA polymerase
: bacteria: one kind, archaea: several kinds, eukarya: several kinds
initiator amino acid for protein synthesis
: bacteria: formyl-methionine, archaea: methionine, eukarya: methionine
membrane liquids: bacteria
: unbranched hydrocarbons, archaea: some branched hydrocarboons, eukarya: unbranched hydrocarbons
introns in genes
: bacteria: very rare, archaea: present in some genes, eukarya: present in many genes
response to the antibiotics streptomycin and chloramphenicol: bacteria
: groeth usually inhibited, archaea: growth not inhibited, eukarya: growth not inhibited
peptidoglycan in cell wall: bacteria
: present, archaea: no, eukarya: no
histones associated with DNA
: bacteria: no, archaea: present in some spaces, eukarya: present
membrane-enclosed organelles
: bacteria: no, archaea: no, eukarya: present
circular chromosome
: bacteria: present, archaea: present, eukarya: no
nuclear envelope
: bacteria: no, archaea: no, eukarya: present
growth at temperatures greater than 100*C
: bacteria: no, archaea: some species, eukarya: no
Archaea
extremophiles
: love extreme conditions
extreme
halophiles
: live in highly saline environments
extreme
thermophiles
: thrive in very hot environments
methanogens
: live in more moderate environments, release methane as by-product to unique ways of obtaining energy
Bacteria
spirochetes
: helical gram-negative heterotrophs, spiral and rotate
chlamydias
: parasites, can only survive in animal cells
proteobacteria
: diverse gram-negative
epsilon
proteobacteria
**
: pathogenic to humans or other animals
delta
proteobacteria: slime-secreting, spores
gamma
proteobacteria: autotrophic
beta
proteobacteria: nutritionally diverse
alpha
proteobacteria: closely related with eukaryotic hosts
cyanobacteria
: gram-negative photoautotrophs, plant-like oxygen-generating photosynthesis
gram-positive bacteria
: rival proteobacteria in diversity, many free-living, one lacks a cell wall
Overview of Prokaryotic Diversity
archaea more closely related to eukaryotes
bacteria are spread out across several lineages
