Bacteria and Archaea Flashcards
What are prokaryotes?
Ancient Organisms
Ubiquitous - occur / thrive almost everywhere including extreme habitats too hostile for most organisms
Successful - due to structural, functional, genetic adaptations
Have simple internal organization ( no nucleus, no membrane - bound organelles)
Classified into two domains based on structure, physiology and biochemistry
Prokaryotes are morphologically simple but metabolically diverse playing a key role in the cycling of matter on Earth
Why are prokaryotes much smaller than eukaryotic protists, plants or animal cells?
Surface Area : Volume ratio limits size that functional cells can attain
Prokaryotic cell “design” reached its size limit.
Prokaryotes use diffusion to get air and nutrients.
What is the structure of a Bacterial Cell?
Internal Cell Structure:
- cytoplasm
- internal membrane (specialized)
- genome organization with nucleoid region and plasmids
- ribosomes
External Cell Structure
- plasma membrane
- cell wall
- flagella
- capsule
- pili
What does a Gram - positive bacterial cell wall mean?
Cell walls contain peptidoglycan.
Peptidoglycan is a polymer of modified sugars cross - linked by short polypeptides
Cell walls of Archaea lack peptidoglycan
What does a Gram - negative bacterial cell wall mean?
Lipopolysaccharides on walls of gram - negative bacteria are often toxic
Outer membrane of gram - negative bacteria more resistant to antibiotics because outer membrane can impede entry to drugs
Many antibiotics inhibit the synthesis of cross - links in peptidoglycans in inner membranes
What is the coccus shape of the bacteria?
A sphere
What is a bacillus shape of a bacteria?
A rod
What is a spirillus shape of a bacteria?
A helix shape
Why are bacterial genomes smaller than eukaryotes?
Bacterial genomes lack non - coding stretches of DNA.
How does diversity rise in prokaryotes?
Diversity in prokaryotes is due to mutations and vertical gene transfer from parent cells to daughter cells (mitosis)
Arterial have some additional unique processes that add genetic diversity called horizontal gene transfer
What are the three types of horizontal gene transfer?
- Conjugation
- Transformation
- Transduction (viruses)
What is the horizontal gene transfer conjugation?
Some bacteria synthesize thin strands of cytoplasm that connect them to other bacteria = pilus (pili)
Pili provide a migration route for direct cell - to - cell transfer of DNA between cells
Process of conjugation commonly transfer plasmids
Spreads novel genes in bacterial populations (e.g. antibiotic resistance)
Plasmids used in genetic engineering techniques (for GMOs)
What is the horizontal gene transfer transformation?
Genes can be transferred from cell - to - cell without direct contact
Cells take up fragments of DNA released into the environment by cell death and breakdown - involves process of transformation
Harmless strains of bacteria could become virulent when exposed to dead cells containing virulent strain
What is the horizontal gene transfer transduction?
Viruses provide another mechanism since viruses can integrate their DNA into host bacterial cells and persist as bacteria divide and grow.
When the virus leaves a bacteria cell and enters into another one, it carries pieces of bacterial DNA and transfers it to the new cell.
Common in nature and as a technique in research labs
What biogeochemical cycles do prokaryotes play a key role in?
Carbon cycle
Oxygen cycle
Sulfur cycle
Nitrogen cycle
What are the roles of photosynthesis and cellular respiration in the carbon cycle?
Photosynthesis is oxygenic
Cellular respiration is aerobic
What cycle is carbon cycling linked to?
Carbon cycling is linked to oxygen cycling
Changes in oxygen levels link evolutionary changes and biological diversity
Evolution of oxygenic photosynthesis by cyanobacteria - key to O2 accumulation in atmosphere
What happens when oxygen is not available?
Deeper layers of microbial mats use a anoxygenic photosynthesis (bacteria have access to light but no oxygen) and anaerobic respiration and fermentation (bacteria don’t have access to either light or oxygen)
Surface layers of the microbial mats that have access to oxygen, CO2 and light use oxygenic photosynthesis and aerobic cellular respiration
What is anoxygenic photosynthesis?
Anoxygenic photosynthesis = CO2 reduced to organic carbon
Absorbs sunlight using a different pigment - bacteriochlorophyll
Uses a single photo system and electron transport chain to produce ATP only
Electron donors are H2S, H2, ferrous iron (Fe++) and arsenite (AsO3 - - -)
What is anaerobic respiration and fermentation?
Without O2, organic molecules are still oxidized to CO2
Oxidants are used as electron acceptors instead of O2.
What is the role of bacteria in the sulfur cycle?
Bacteria oxidize H2S to sulfate from decomposing organisms
This allows the plants to absorbs the sulfate and it to enter the sulfur cycle
After the plants it goes to the animals through consumption of plants and then back to the bacteria when animals die
What is the role of bacteria in the nitrogen cycle?
Bacteria can convert nitrogen gas in the air to NH3 that can be made into biomolecules. Called nitrogen fixation.
Plants such as soy beans have nodules that bacteria live in and preform nitrogen fixation.
Nitrification is the process when NH3 from dead organisms is converted to NO3- by bacteria
Denitrification is when anaerobic respiration converts nitrate back into nitrogen gas and the cycle starts again
What is the anammox reaction?
The anammox (anaerobic ammonia oxidation) reaction is:
NH4+ + NO2- = N2 + water
In archaea
Domain = prokaryotes Classification = bacteria
What are the 6 important groups of bacteria?
- Proteobacteria
- Green bacteria
- Cyanobacteria
- Gram - positive bacteria
- Spirochetes
- Chlamydias
What are proteobacteria?
The most diverse of all bacterial groups
Gram - negative bacteria
- purple sulfur bacteria
- colour due to unique type of chlorophyll
- photoautotrophic or photoheterotrophic
Free - living gram negative proteobacteria
- chemheterotrophs
- intestinal bacteria (E. coli)
- some cause human disease (e.g. gonorrhea, gastroenteritis)
What is green bacteria?
Gram - negative photosynthetic bacteria
- found in hot springs (photoautotrophic)
- marine and high - salt environments (photoheterotropic)
- distinctive chlorophyll compared to plants
- do not release oxygen as by - product of photosynthesis
What is Cyanobacteria (= blue green algae)?
Gram - negative aerobic photosynthetic prokaryotes
- responsible for oxygen - based life on Earth
- most morphologically diverse group of bacteria
- some species may form colonies
- some species have specialized cell types (e.g. hetercysts for nitrogen fixation)
What is gram - positive bacteria?
- primarily chemoheterotrophs
- many pathogenic species
- some beneficial species
What is spirochetes ( gram - negative bacteria)?
- propelled by rotation of helically sprialled flagella
- enables movement in thick mud / sewage
- beneficial or harmless species
- found in human mouth
- in termite intestines that digest cellulose
- pathogenic species (e.g. syphilis)
What is chlamydias (gram - negative bacteria)?
- cell walls with membrane outside
- lack peptidoglycans
- intercellular parasites that cause diseases in animals
What is a special feature of Deinococcus radiodurans?
- tolerant radiation
- can break down radioactive waste
What is a special feature of Thermus aquaticus?
- tolerant to high temperatures
- enzyme DNA polymerase is very heat - stable
Domain = prokaryotes Classification = Archaea
What are some unique features of Archaea?
- they have some feature like bacteria such as being prokaryotes, the chromosomes, ribosomes)
- they have some features like eukaryotes such as histones and enzymes
- they have some unique features such as membranes and protein synthesis
What are the 5 evolutionary branches of Archaea?
- Crenarchaeota
- Korarcheota
- Thaumarchaeota
- Euryarchaeota
- Nanoarchaeota
Use the tolerance / adaptations to extreme environmental conditions as clues to evolutionary relationships
What are Euryarchaeota Methanogens?
Methane generators
Live in low - oxygen environments
Obligate anaerobes in:
- anoxic sediments of swaps, lakes, marshes, sewage works
- large intestine of dogs and humans
- hindguts of insects
- in rumen of cattle, sheep, etc.
What are Euryarchaeota Halophiles (“salt - loving”)
Live in highly saline environments
Aerobic chemoheterotrophs
- obtain energy from sugars, alcohols, amino acids
- some use light as a secondary energy source
What is Euryarchaeota Extreme Thermophiles (“heat loving”)?
Live in extremely hot environments
- hydrothermal vents and hot springs
- tolerate temperatures between 70°C to 95°C
What is Crenarchaeota Extreme Thermopiles?
Higher optimal temperature range than Euryarchaeota organisms
What are Crenarchaeota Psychrophiles (“cold - loving”)?
Thrive at temperatures between -10°C to -20°C
Found in Antarctica and arctic oceans
What are Crenarchaeota Mesophiles?
Many plankton in cool marine waters
What is Korarchaeota?
Recognized only by sequences in DNA samples
Found in hydrothermal environments but have never been isolated and cultivated in lab
Nothing known about their physiology
What are the Thaumarchaeota?
May be the most abundant cells in the oceans
Chemoautotrophs that use ammonia (involved in Anammox reaction in nitrogen cycle)
What is the evolutionary history of prokaryotes?
Phylogeny of bacteria and Archaea is still a work in progress
Evolution of bacteria and Archaea should be viewed as an intertwined network instead of a tree
Why are prokaryotes important to study?
They help us to better understand disease transmission and treatments
They help us better understand symbiotic relationships with other organisms, especially for humans with the human microbiology
They help us understand the role of prokaryotes and ecosystem processes
They help us understand ways to use these organisms in biotechnology
They teach us about adaptability and living sustainably through biomimicry
What is periodic selection?
Periodic selection is the episodic of loss of diversity
Biologist observed that genetic diversity in laboratory cultures gradually increases through time and then rapidly decreases with the emergence of a successful variant that it competes the rest
Some biologists argue that this process provides a means of recognizing bacterial species
How much to bacteria out number our own cells?
10 bacteria cells to 1 human cell
