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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
first prokaryotes lived 3.5 billion years ago
prokaryotic cells typically have smaller diameter than eukaryotic cells
prokaryotes are well organized
common shapes of prokaryotes are cocci, bacilli, spirilla
Cell-Surface Structures
key feature of all prokaryotic cells is the cell wall
prokaryotes can lose water in hypertonic environment
inhibit cell reproduction
cell walls of eukaryotes differ from those of prokaryotes
Eukaryotic cell walls are made of cellulose or chitin
bacterial cell walls are made of peptidoglycan
Archael cell walls contain polysaccharides but lack peptidoglycan
Gram stain: how scientists categorize bacterial species by differences in cell wall composition
gram positive: simple cell walls composed of a thick layer of peptidoglycan
gram negative: have less peptidoglycan and more complex structurally; outer membrane contains lipopolysaccharides
valuable tool in medicine
gram negative bacteria tend to be more resistant to antibiotics because the outer membrane impedes the entry
some gram positive species have virulent strains that can be resistant to one or more antibiotics
Prokaryotes are surrounded by a sticky layer of polysaccharide or protein
capsule: well defined
slime layer: not well organized
both layers enable prokaryotes to adhere to their substrate
Endospores: resistant cell produced by some bacterial cells when they are exposed to harsh conditions
most endospores can withstand boiling water
can remain dormant in less hostile environments
Fimbrae: hair-like appendages that help prokaryotes stick to another or their substrate
Ex: bacteria that causes gonorrhea
Motility
Prokaryotic flagella differ greatly from eukaryotic flagella
molecular composition and their mechanism of propulsion
Bacterial and Archael flagella have similar size and rotational mechanism; have different unrelated proteins
flagella of bacteria, archaea, and eukaryotes are described as analogous
Evolutionary Origins of Bacterial Flagella
evidence indicates bacterial flagella originated a simpler structures and were modified
Exaptation: process in which structures originally adapted for one function take on new functions through w/ modification
bacterial flagellum evolved as other proteins were added to an ancestral secretory system
Internal Organization and DNA
prokaryotic cells lack complex compartmentalization associated w/ the membrane enclosed organelles
some prokaryotic cells have membranes that perform metabolic functions
store metabolic by-products in simple compartments made out of protein
genome of prokaryotes is structurally different from a eukaryotic genome
prokaryotic has less DNA
prokaryotes have circular chromosomes; eukaryotes have linear chromosomes
prokaryotes chromosomes are associated w/ fewer proteins
prokaryotes lack nucleus; chromosome located in nucleoid
prokaryotic cells have plasmids
Prokaryotic ribosomes are smaller than eukaryotic ribosomes; differ in their protein and RNA content
Reproduction
prokaryotes reproduce by binary fission
many prokaryotes can divide every 1-3 hours
Concept 27.2: Rapid reproduction, mutation, and genetic recombination
Rapid Reproduction and Mutation
new mutations can increase genetic diversity
binary fission
Genetic Recombination
Combining of DNA from two sources
meiosis and fertilization
transformation, transduction, and conjugation bring together prokaryotic DNA
Horizontal gene transfer: when individuals are members of different species this is the movement of genes from organism to another
Transformation and Transduction
Transformation: the genotype and possibly phenotype of a prokaryotic cell are altered by the uptake of foreign DNA from its surroundings
R Plasmids and Antibiotic Resistance
some bacteria have resistance genes which code for enzymes that specifically destroy or hinder the effectiveness of antibiotics
resistance genes are carried by R plasmids
Some R plasmids carry genes for resistance to as many as ten antibiotics
Concept 27.3: Diverse nutritional and metabolic adaptations have evolved in prokaryotes
Genetic variations in prokaryotes is found in their nutritional adaptations
phototrophs: obtain energy from light
chemotrophs: obtain energy from chemicals
autotrophs: require CO2 or related compounds as a carbon source
Heterotrophs: require an organic nutrient to make organic compounds
Table 27.1: Major Nutritional Modes
Autotroph
Photoautotroph
Energy Source
Light
Carbon Source
CO2 or HCO3 or related compound
Types of organisms
Photosynthetic prokaryotes
Chemoautotroph
Energy Source
Inorganic Chemicals
Carbon Source
CO2 or HCO3 or related compound
Types of Organisms
Sulfolobus
Heterotroph
Photoheterotroph
Energy Source
Light
Carbon Source
Organic Compounds
Types of Organisms
salt loving prokaryotes
Chemoheterotroph
Energy Source
Organic Compounds
Carbon Source
Organic Compounds
Types of Organisms
Many prokaryotes and protists
Metabolic Cooperation
cooperation between prokaryotic cells allow them to use environmental resources
heterocyst: cell that engages in nitrogen fixation in some filamentous bacteria
Biofilms: surface-coating colonies
cells secret signaling molecules that recruit nearby cells
channels in the biofilm allow nutrients to reach cell in the interior and wastes to be expelled
Concept 27.4: Lineage Diversity
Prokaryotic Diversity
immense diversity of prokaryotes
genomes can be obtained from environmental samples using metagenomics
Horizontal gene transfer has played a key role in the evolution of prokaryotes
Table 27.2
Bacteria
nuclear envelope absent
membrane organelles absent
peptidoglycan in cell wall
membrane lipids: unbranched hydrocarbons
Initiator Amino Acid: Formylmethionine
Archaea
nuclear envelope absent
membrane organelles absent
peptidoglycan absent
membrane lipids: some branched hydrocarbons
Initiator amino acid: Methionine
Introns in genes: present in some genes
Eukarya
nuclear envelope present
organelles present
peptidoglycan absent
membrane lipids: unbranched hydrocarbons
Initiator Amino Acid: Methionine
Introns in genes: present in many genes
Archaea
First prokaryotes assigned to domain Archaea that live in extreme conditions
extremophiles: lover of extreme conditions
extremhalophiles: live in highly saline environments
extremethermophiles: thrive in very hot environments
methanogens: release methane as a by-product of their unique ways of obtaining energy
Concept 27.5: Prokaryotes in the Biosphere
Chemical Recycling
Decomposers: breaking down dead organisms as well as waste products and thereby unlocking supplies of carbon, nitrogen, and other elements
Ecological Interactions
mutualism: both benefit
parasitism: one harmed/ one benefit
commensalism: one benefits/ one not affected
parasite: eats the cell contents, tissues or body fluids of host
host: large participant in symbiotic relationship
pathogen: organism or virus that causes disease
symbiont: smaller participant in symbiotic relationship
Concept 27.6
Mutualistic Bacteria
Human intestines are home to about 500-1000 species of bacteria
many of these are mutualists and break down food that is undigested by our intestines
Ex: Vitamin K
Pathogenic Bacteria
Bacteria cause about half of all human diseases
Some bacterial diseases can be transmitted by other organisms
Ex: Lyme disease from Ticks
Exotoxins: proteins secreted by certain bacteria and other organisms
Endotoxins: lipopolysaccharide components of the outer membrane of gram-negative bacteria
