Origin of microbial life, evolution, and modern diversity Flashcards
Describe the de Novo hypothesis of the origin of life on Earth
Life originated on Earth from a primordial non-oxidising atm including of H2O, H2, CO2, and N
Describe the Panspermia hypothesis of the origin of life on Earth
Life arrived on Earth, preformed as spores, enveloped in mantle formed by a collision between between a life-bearing planet and comet/meteorite
What must be true is the de Novo hypothesis is true?
The assembly of macromolecules into primitive wells would have included the evolution of proteins to RNA to DNA
What would have happened to protocells in the de Novo hypothesis?
They would have evolved to LUCA and then to modern prokaryotic cells
Describe LUCA
Anaerobic, hyperthermophilic, halophilic, and chemolithotrophic
Where did LUCA obtain energy and carbon from?
Inorganic sources
Used H2 and H2S as e- donors and CO2 as e- accpetor
Fixed CO2 as carbon source
According to the organic soup theory, what would the first prokaryotic cells have been?
Heterotrophs that could live without free oxygen
Fed on externally available, abiotically synthesised organic molecules
Why did autotrophy emerge?
To sustain life because abiotic synthesis was rate-limiting and the demand could not be met
Describe the two types of autotrophs that emerged to sustain life
Chemolithotrophs obtain energy from oxidation of inorganic compounds
Photolithotrophs obtain energy by converting sunlight into chemical energy
According to the surface metabolist theory, what would the first cells have been?
Autotrophs
What conditions allowed the evolution of the first eukaryotic organisms?
Protection from U.V. by the ozone layer
Increased O2 acts as e- acceptor for high energy metabolism
What orgenelles were needed by new photosynthesising and respiring cells?
Chloroplasts and mitochondria (respectively)
How were the first chloroplasts and mitochondria developed?
Endosymbiosis of primitive cells and cyanobacteria-like organisms
What are Whittaker’s 5 Kingdoms based on?
Nutrition (photosynthesis, absorption, ingestion)
Dominated by plants, fungi, and animals
What are Woese’s 3 Domains based on?
Evolutionary relationships inferred by sequence comparision (rRNA genes)
Dominated by microorganisms
Why is there bias in our understanding of microbial diversity?
It is largely based on cultured organisms
What is the result of prokaryotes being less limited than eukaryotes by conditions?
They have a higher proportion of carbon biomass
What is the most physiologically diverse bacterial group? What are the five types?
Proteobacteria
α, β, γ, δ, ε
Briefly describe alphaproteobacteria
Agricultural importance
Includes nitrate oxidisers, and N-fixers
Includes purple non-sulphur bacteria (anoxygenic photosynthesis)
Briefly describe betaproteobacteria
Biotechnological importance
Includes soil contaminant degraders
Briefly describe deltaproteobacteria
Includes sulphate-reducers and Fe(III), Mn(IV), and S-reducers
Briefly describe gammaproteobacteria
Includes anoxygenic photosynthetic purple sulphur bacteria
Briefly describe epsilonproteobacteria
Includes chemolithotrophic sulphur bacteria
Includes types of digestive system pathogens
Describe green sulphur bacteria
Anoxygenic photosynthetic bacteria that use sulphide (not water) as e- donor for reducing CO2 fixation
