2.) 3 Domains, Bacteria & Archaea
Why are organisms grouped in separate categories?
To make sense of the past and present diversity of life on Earth - via classification systems
Why was the evolution of aerobic respiration important?
- Aerobic respiration = more efficient, produces more energy - Oxygen is a more efficient e- acceptor b/c it is highly electronegative - More potential energy in glucose can be released when oxygen is final e- acceptor compared to other molecules/ions (e.g., nitrate, iron)
Prokaryotes in the nitrogen cycle
- Bacteria & archaea drive the nitrogen cycle through the atmosphere and ecosystems
bacteria vs. archaea (morphology)
- Bacteria = peptidoglycan in cell walls - Archaea = no peptidoglycan; hydrocarbon tail of phospholipids in cell membrane have branched isoprene chains
What are the three domains of life?
- Bacteria, Archaea, & Eukarya - Original 5 Kingdom classification system based on morphology and cell structure - 3 Domain system based on molecular phylogeny = differences in ribosomal RNA (rRNA)
nitrify
- Conversion of ammonia (NH3) to nitrites (NO2-) or nitrates (NO3-) - NH3 → NO2- or NO3-
denitrify
- Conversion of nitrates (NO3-) to molecular nitrogen (N2) - NO3- → N2
protists
- Eukaryote that is not a plant, animal, or fungus - Mostly unicellular; multicellular protists do not show cellular specialization or differentiation into tissues (e.g., kelp) - Highly diverse - Chloroplasts passed around to other lineages of protists via secondary endosymbiosis
secondary endosymbiosis
- Eukaryotic cell engulfs another eukaryotic cell that has undergone primary endosymbiosis 1. Predatory protist consumes photosynthetic protist *Organelle has 4 membranes
cyanobacteria
- First organisms to perform oxygenic ("oxygen-producing") photosynthesis
Role of cyanobacteria - early Earth
- For first 2.3 billion yrs of Earth, no free molecular oxygen (O2) - Only anaerobic respiration was possible - Cyanobacteria responsible for producing original source Earth's free oxygen - Triggered evolution of aerobic respiration
horizontal gene transfer (HGT)
- Genetic similarities between 3 domains suggest HGT between bacteria & archaea was an important factor in the evolution of prokaryotes - Eukarya has traits of both prokaryote lineages - Eukarya may have arose from symbiosis of archaeal and bacterial cell
primary endosymbiosis
- Living cell engulfs prokaryote 1. Archael cell engulfs aerobic bacterium → eukaryotic cell w/ mitochondria 2. Eukaryote w/ mitochondria engulfs cyanobacterium → photosynthetic eukaryote (mainly Plantae)
How does the metabolic diversity of prokaryotes enhance their environmental diversity?
- Metabolic of diversity of bacteria & archaea allow them to live in a variety of habitats - Able to use various e- donors, acceptors, and fermentation substrates - Able to use different types of photosynthesis
What makes a bacteria pathogenic?
- Most bacteria are harmless - only a small % are pathogenic - Possess genes for virulence, or the ability to cause disease - Genes code for a protein toxin
eukaryotes
- Multicellular - Membrane-bound nucleus - DNA enclosed in nucleus - 1 domain = Eukarya
nitrogen fixation
- N2 → NH3 - Conversion of N2 (atmospheric nitrogen) to NH3 (ammonia, which can be used by living organisms) - Nitrogen-fixing bacteria found in root nodules of legumes and in soil
toxin
- Toxin enters host cell, binds to ribosomes and inhibits protein synthesis → kills host cell
prokaryotes
- Unicellular - No membrane-bound nucleus - DNA suspended in cytoplasm - 2 domains = Bacteria & Archaea
bacteria
- Unicellular prokaryotes - Producers, consumers, & decomposers, nitrogen fixation - E.g., cyanobacteria (photosynthesizing - related to eukaryotic chloroplasts), proteobacteria, spirochaetes, etc.
archaea
- Unicellular prokaryotes - Producers, decomposers - E.g., extremophiles = methanogens ("methane makers"), halophiles ("salt-loving"), thermophiles ("hot/cold lovers) - More closely related to Eukarya than Bacteria; Archaea and Eukarya share more recent common ancestor - Shares similar RNA polymerases, DNA polymerases, transcription-initiation proteins, and ribosomes to Eukarya that are NOT found in bacteria
Nitrogen Cycle
1. Atmospheric nitrogen (N2) 2. Nitrogen-fixing prokaryotes: convert molecular nitrogen to ammonia (N2 → NH3) 3. Nitrifying prokaryotes: convert ammonia to nitrite or nitrate (NH3 → NO2- or NO3-) 4. Denitrifying prokaryotes: convert nitrate to molecular nitrogen (NO3- → N2)
taxonomic rank
1. Domain (Dear) 2. Kingdom (King) 3. Phylum (Philip) 4. Class (Came) 5. Order (Over) 6. Family (For) 7. Genus (Good) 8. Species (Soup)
Koch's Postulates
1. Microorganism must be present in organisms suffering from the disease, but not in healthy organisms 2. Microorganism must be isolated from diseased organism and grown in pure culture 3. Cultured microorganism should cause disease when inoculated into a healthy organism 4. Microorganism must be reisolated from the new diseased host and shown to be identical to the original inoculated pathogen
pathogen
Microorganism that can cause disease
autotroph
Obtain carbon from CO2 (an inorganic molecule)
heterotroph
Obtain carbon from organic molecules (e.g., glucose) - Organic molecules can come from living hosts or from wastes products of dead organisms
chemotroph (prokaryotes)
Obtain energy from inorganic OR organic subtances - Chemoautotroph = 1.) obtains energy by oxidizing INORGANIC substances (e.g., hydrogen, iron, sulfur, ammonia, nitrates, nitrites) and 2.) obtains carbon from CO2 - Chemoheterotroph = 1.) obtains energy by oxidizing ORGANIC substances and 2.) obtains carbon from organic molecules
phototroph (prokaryotes)
Obtain energy from light - Photoautotroph = 1.) obtains energy from light via photosynthesis and 2.) obtains carbon from CO2 - Photoheterotroph = 1.) obtains energy from light via synthesis and 2.) obtains carbon from organic carbon molecules
carbon fixation
Process of converting inorganic carbon (CO2) to organic compounds by living organisms (e.g., plants, cyanobacteria)